Encapsulation and Controlled Release Technologies in Food Systems, 0813828554

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Encapsulation and Controlled Release Technologies in Food Systems

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Encapsulation and Controlled Release Technologies in Food Systems Edited by Jamileh M. Lakkis

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Jamileh M. Lakkis, Ph.D., has 14 years experience in the food, dietary supplements, and consumer products industries. She served as Senior Project Manager at Pfizer/Cadbury-Schweppes, Morris Plains, NJ, focusing on designing confectionery products as delivery systems for oral care benefits. As a Senior Encapsulation Specialist for General Mills, Inc., Minneapolis, MN, Dr. Lakkis designed several microencapsulation processes for stabilizing and masking the taste/aroma of a variety of functional and nutraceutical actives for their applications in breakfast cereals, dairy, confections, and shelf-stable bakery products. Her professional experience also includes engagements as Senior Research Scientist at Land O’Lakes, Inc., Arden Hills, MN. Dr. Lakkis co-organized the first IFT symposium on microencapsulation and controlled release applications in food systems. She is an active member of the Controlled Release Society and serves on the society’s newsletter editorial board representing the Consumer and Diversified Products Division. ©2007 Blackwell Publishing All rights reserved Blackwell Publishing Professional 2121 State Avenue, Ames, Iowa 50014, USA Orders: 1-800-862-6657 Office: 1-515-292-0140 Fax: 1-515-292-3348 Web site: www.blackwellprofessional.com Blackwell Publishing Ltd. 9600 Garsington Road, Oxford OX4 2DQ, UK Tel.: +44 (0)1865 776868 Blackwell Publishing Asia 550 Swanston Street, Carlton, Victoria 3053, Australia Tel.: +61 (0)3 8359 1011 Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Blackwell Publishing, provided that the base fee is paid directly to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payments has been arranged. The fee codes for users of the Transactional Reporting Service is ISBN-13: 978-0-8138-2855-8/2007. First edition, 2007 Library of Congress Cataloging-in-Publication Data Encapsulation and controlled release technologies in food systems / edited by Jamileh M. Lakkis, Ph. D.—1st ed. p. cm. Includes bibliographical references and index. ISBN 978-0-8138-2855-8 (alk. paper) 1. Controlled release technology. 2. Microencapsulation. 3. Food—Analysis. I. Lakkis, Jamileh M. TP156.C64E53 2007 664'.024—dc22 2007006839 The last digit is the print number: 9 8 7 6 5 4 3 2 1

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I dedicate this book to LEBANON Which had not been my country, I’d have chosen it to be

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Table of Contents

Dedication Contributors Preface Jamileh M. Lakkis

v ix xi

1. Introduction Jamileh M. Lakkis

1

2. Improved Solubilization and Bioavailability of Nutraceuticals in Nanosized Self-Assembled Liquid Vehicles Nissim Garti, Eli Pinthus, Abraham Aserin, and Aviram Spernath

13

3. Emulsions as Delivery Systems in Foods Ingrid A.M. Appelqvist, Matt Golding, Rob Vreeker, and Nicolaas Jan Zuidam

41

4. Applications of Probiotic Encapsulation in Dairy Products Ming-Ju Chen and Kun-Nan Chen

83

5. Encapsulation and Controlled Release in Bakery Applications Jamileh M. Lakkis 6. Encapsulation Technologies for Preserving and Controlling the Release of Enzymes and Phytochemicals Xiaoyong Wang, Yan Jiang, and Qingrong Huang 7. Microencapsulation of Flavors by Complex Coacervation Curt Thies 8. Confectionery Products as Delivery Systems for Flavors, Health, and Oral-Care Actives Jamileh M. Lakkis 9. Innovative Applications of Microencapsulation in Food Packaging Murat Ozdemir and Tugba Cevik 10. Marketing Perspective of Encapsulation Technologies in Food Applications Kathy Brownlie Index

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Contributors

Ingrid A.M. Appelqvist Unilever Food and Health Research Institute Unilever R&D Vlaardingen The Netherlands Chapter 3

Nissim Garti Casali Institute of Applied Chemistry The Institute of Chemistry The Hebrew University of Jerusalem Jerusalem, Israel Nutralease Ltd., Mishor Adumim, Israel Chapter 2

Abraham Aserin Casali Institute of Applied Chemistry The Institute of Chemistry The Hebrew University of Jerusalem Jerusalem, Israel Nutralease Ltd., Mishor Adumim, Israel Chapter 2

Matt Golding Unilever Food and Health Research Institute Unilever R&D Vlaardingen The Netherlands Chapter 3

Kathy Brownlie Manager, Global Programme Frost & Sullivan Oxford, England, UK Chapter 10

Qingrong Huang Department of Food Science Rutgers University New Brunswick, NJ Chapter 6

Tugba Cevik Department of Chemical Engineering Section of Food Technology Gebze Institute of Technology Gebze-Kocaeli, Turkey Chapter 9

Nicolaas Jan Zuidam Unilever Food and Health Research Institute Unilever R&D Vlaardingen The Netherlands Chapter 3

Kun-Nan Chen Department of Mechanical Engineering Tung Nan Institute of Technology Taipei, Taiwan Chapter 4 Ming-Ju Chen Department of Animal Science National Taiwan University Taipei, Taiwan Chapter 4

Yan Jiang Department of Food Science Rutgers University New Brunswick, NJ Chapter 6 Jamileh Lakkis Senior Project Manager Formerly with Pfizer/Cadbury-Schweppes Morris Plains, NJ Chapter 1 Chapter 5 Chapter 8

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Contributors

Murat Ozdemir Department of Chemical Engineering Section of Food Technology Gebze Institute of Technology Gebze-Kocaeli, Turkey Chapter 9 Eli Pinthus Nutralease Ltd., Mishor Adumim, Israel Adumim Food Ingredients Mishor Adumim, Israel Chapter 2 Aviram Spernath Casali Institute of Applied Chemistry The Institute of Chemistry The Hebrew University of Jerusalem Jerusalem, Israel Chapter 2

Curt Thies Thies Technology Henderson, Nevada Chapter 7 Rob Vreeker Unilever Food and Health Research Institute Unilever R&D Vlaardingen The Netherlands Chapter 3 Xiaoyong Wang Department of Food Science Rutgers University New Brunswick, NJ Chapter 6

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Preface

Encapsulation and controlled release technologies have enjoyed their fastest growth in the last two decades. These advances, pioneered by pharmaceutical companies, were a result of: (1) the rapid change in drug development strategies to target specific organs or even cells, (2) physicians’ growing concern about patient non-compliance, and (3) pharmaceutical companies desire to extend their market monopoly on new drugs for a certain period of time as provided by the US and international patent laws. Despite this progress, encapsulation and controlled release technologies have only been recently adopted by the food industry. Food researchers and technologists have often been confronted with the dilemma of how to translate all these advances from the drug arena into practical applications in food systems. By searching the literature, one can find volumes of books and specialized publications on encapsulation and controlled release technologies. Unfortunately, most of these publications have dealt with theoretical aspects of these technologies with little emphasis on real applications in consumer and food products. This book attempts to illustrate various aspects of encapsulation and controlled release applications in food systems using practical examples. These examples will give the reader an appreciation for the delicate art of designing encapsulated ingredients and the enormous challenges in incorporating them into food formulations. Most of the practical examples in this book were borrowed from the patent literature. This approach might be questioned based on the fact that patents applications are never peer reviewed, but seems justifiable considering the frantic effort by both industry and academia to protect their discoveries and to gain limited-time monopoly on their innovations, thus limiting the availability of such information in peer-reviewed articles. This publication has several potential uses. It is a reference book for scientists in the food, nutraceuticals and consumer products industries who are looking to introduce microencapsulated ingredients into new or existing formulations. It is also a post-graduate text designed to give students some comprehension of various aspects of encapsulation and controlled release in food systems. This book is organized in such a way that each chapter treats one major application of encapsulation and controlled release technologies in foods. Chapter 1 introduces the readers to various encapsulation and controlled release technologies, as well as release mechanisms, suitable for applications in foods, nutraceuticals and consumer products. Chapter 2 by Professor Nissim Garti and his collaborators discusses a novel approach to encapsulation and controlled release via reverse microemulsion technique referred to as nanosized self-assembled liquids (NSSL). Such systems are shown to provide exceptional thermodynamic stability in a wide pH range. In addition to enhancing bioavailability of functional active ingredients, NSSL systems, by virtue of their unique transparent appearance, are excellent candidates for beverage applications. Chapter 3, by Dr. Klaas-Jan Zuidam and co-workers, presents an elaborate approach to understanding emulsions and their benefits as delivery systems in food applications. This chapter discusses various mechanisms of emulsion stabilization and destabilization and

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Preface

how they can best be designed for targeted delivery of flavors and functional ingredients in the human gastrointestinal system. Chapter 4 on encapsulation and controlled release of probiotics by Drs. Chen and Chen reports on approaches for encapsulating probiotic bacteria in dairy products as well as in the human gastrointestinal tract. This chapter also discusses novel optimization techniques for stabilizing these beneficial bacteria and enhancing their survival rates. Chapter 5, written by the editor of this book, highlights current approaches to encapsulation and controlled release technologies for bakery products applications. Current encapsulation practices such as hot-melt particle coating and spray chilling are discussed. Examples of the performance of encapsulated leavening agents as well as sweeteners and flavors are presented in shelf-stable bakery applications. Chapter 6 on nanoencapsulation technology by Dr. Huang and his collaborators deals with novel approaches to encapsulate enzymes and nutraceuticals. Specific examples are presented on stabilization of phytochemicals and their enhanced bioavailability via incorporation into nanoemulsions and bioconjugation systems. Chapter 7 on flavor encapsulation via complex coacervation is written by Dr. Curt Thies. Discussion is focused on the basic principle of complex coacervation technique as a liquid– liquid polymer phase separation phenomenon. Guidance on polymer selection and subsequent implications on the physicochemical properties of capsules as well as their release behavior is provided. Chapter 8, written by the editor of this book, details techniques used for delivering therapeutic as well as functional actives and flavors via confectionery products. Technologies and subsequent applications discussed in this chapter have wide applications in the food, nutraceuticals, as well as pharmaceutical arenas. Mechanisms and challenges specific to targeted release in upper gastrointestinal tract, especially the mouth and throat areas will be described in great detail. Chapter 9 discusses encapsulation and controlled release of actives in packaging applications by Dr. Ozdemir and collaborator. In this contribution, the authors provide examples on embedding fragrances, pigments as well as antimicrobial and insect repellent agents into food packaging films. Chapter 10, authored by Ms. Kathy Brownlie, provides a marketing perspective of microencapsulation technologies and their potential impact on the food industry. Ms. Brownlie offers an in-depth assessment of market drivers as well as constraints that are still hindering wider implementation of these technologies in food manufacturing. This book has definitely surpassed my vision and expectations thanks to the contributors that I am grateful to all of them for their expertise, commitment, and dedication. It is my hope that this book will prove itself a useful source on encapsulation and controlled release in a wide range of food and consumer product applications. Many thanks to the editorial staff at Blackwell Publishing Co., especially to Mark Barrett and Susan Engelken for their valuable help and advice throughout this project. Last but not least, I would like to thank my parents who taught me the importance of working hard, having clear goals, and standing for what I believe is right. It is a lesson that guides me in everything I do. Jamileh M. Lakkis

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Encapsulation and Controlled Release: Technologies in Food Systems Edited by Jamileh M. Lakkis Copyright © 2007 by Blackwell Publishing

1

Introduction Jamileh M. Lakkis

The European Directive (3AQ19a) defines controlled release as a “modification of the rate or place at which an active substance is released.” Such a modification can be made using materials with specific barrier properties for manipulating the release of an active and to provide unique sensory and/or functional benefits. Addition of small amounts of nutrients to a food system, for example, may not affect its properties significantly; however, incorporating high levels of the nutrient either to meet certain requirements or to treat an ailment will most often result in unstable and often unpalatable foods. Examples of such nutrients include fortification with calcium, vitamins, polyunsaturated fatty acids, and so on, and the associated grittiness, medicinal and oxidized taste, respectively. Different types of controlled-release systems have been formulated to overcome these challenges and to provide a wide range of release requirements. The two principal modes of controlled release are delayed and sustained release (Figure 1.1). • Delayed release is a mechanism whereby the release of an active substance is delayed from a finite “lag time” up to a point when/where its release is favored and is no longer hindered. Examples of this category include encapsulating probiotic bacteria for their protection from gastric acidity and further release in the lower intestine, flavor release upon microwave heating of ready-meals or the release of encapsulated sodium bicarbonate upon baking of a dough or cake batter. • Sustained release is a mechanism designed to maintain constant concentration of an active at its target site. Examples of this release pattern include encapsulating flavors and sweeteners for chewing gum applications so that their rate of release is reduced to maintain a desired flavor effect throughout the time of chewing. A wide range of cores (encapsulants), wall-forming materials (encapsulating agents), and technologies for controlling the interactions of ingredients in a given food system and for manufacturing microcapsules and microparticles of different size, shape, and morphological properties are commercially viable.

Wall-Forming Materials Materials used in film coating or matrix formation include several categories: 1. Waxes and lipids: beeswax, candelilla and carnauba waxes, wax micro- and wax macroemulsions, glycerol distearate, natural and modified fats. 2. Proteins: gelatins, whey proteins, zein, soy proteins, gluten, and so on. All these proteins are available both in native and modified forms.

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Chapter 1

Sustained (long-lasting) release

Delayed release time Figure 1.1.

Generic representation of “sustained” and “delayed” release profiles.

3. Carbohydrates: starches, maltodextrins, chitosan, sucrose, glucose, ethylcellulose, cellulose acetate, alginates, carrageenans, chitosan, and so on. 4. Food grade polymers: polypropylene, polyvinylacetate, polystyrene, polybutadiene, and so on.

Core Materials Core materials include flavors, antimicrobial agents, nutraceutical and therapeutic actives, vitamins, minerals, antioxidants, colors, acids, alkalis, buffers, sweeteners, nutrients, enzymes, cross-linking agents, yeasts, chemical leavening agents, and so on.

Release Triggers Encapsulation and controlled-release systems can be designed to respond to one or a combination of triggers that can activate the release of the entrapped substance and to meet a desired release target or rate. Triggers can be one or a combination of the following: • • • • • •

temperature: fat/wax matrices moisture: hydrophilic matrices pH: enteric coating, emulsion coalescence, and others. Enzymes: enteric coating as well as a variety of lipid, starch and protein matrices. Shear: chewing, physical fracture, and grinding lower critical solution temperature (LCST) of hydrogels.

Payload is a term used to estimate the amount of active (core) entrapped in a given matrix or wall material (shell). Payload is expressed as: Payload (%) = [(core)/(core + shell)] × 100


Introduction

3

Entrapment of Actives in Food Matrices Entrapment in an Amorphous Matrix Encapsulation of active into an amorphous matrix, generally, involves melting a crystalline polymer using heat and/or shear to transform the molecular structure into an amorphous phase. The encapsulant is then incorporated into the metastable amorphous phase followed by cooling to solidify the structure and form glass, thus restricting molecular movements. Carbohydrates are excellent candidates for encapsulation applications due to the several attributes possessed by them. 1. 2. 3. 4.

They form an integral part of many food systems. They are cost-effective. They occur in a wide range of polymer sizes. They have desirable physicochemical properties such as solubility, melting, phase change and so on.

Sucrose, maltodextrins, native and modified starches, polysaccharides, and gums have been used in encapsulating flavors, minerals, vitamins, probiotic bacteria as well as pharmaceutical actives. The unique helical structure of the amylose molecule, for example, makes starch a very efficient vehicle for encapsulating molecules like lipids, flavors, and so on (Conde-Petit et al., 2006). Some carbohydrates such as inulin and trehalose can provide additional benefits for encapsulation applications. Inulin, for example, is a prebiotic ingredient that can enhance survival of probiotic bacteria while trehalose serves as a support nutrient for yeasts. Two main technologies—spray drying and extrusion—have been used in large-scale encapsulation applications into amorphous matrices, though using different mechanisms. In spray drying, for example, the active is trapped within porous membranes of hollow spheres, while in extrusion the goal is to entrap the active in a dense, impermeable glass. Encapsulating actives via spray drying requires emulsifying the substrate into the encapsulating agent. This is important for flavor applications, in particular, considering the fact that most flavors are made up of components of various chemistries (polarity, hydrophobic to hydrophilic ratios), thus limiting their stability when dispersed or suspended in different solvents. Hydrophobicity is one of the most critical attributes that can play a significant role in determining flavors’ payload as well as their release in food systems. The basic principle of spray drying has been adequately covered by Masters (1979). Briefly, the process comprises atomizing a micronized (1–10 micron droplet size) emulsion or suspension of an active and an encapsulating substance and further spraying the same into a chamber. Drying takes place at relatively high temperatures (210°C inlet and 90°C outlet), though the emulsion’s exposure to these temperatures lasts only for few seconds. The process results in free flowing, low bulk density powders of 10–100 micron size. Optimal payloads of 20% can be expected for flavors encapsulated in starch matrices. Maltodextrins and sugars with lower molecular weight, due to their low viscosities and inadequate emulsifying activities, result in lower flavor payloads. Several factors can impact the efficiency of encapsulation via spray drying, mainly those related to the emulsion (solid content, molecular weight, emulsion droplet size, and viscosity) and to the process (feed flow rate, inlet/outlet temperature, gas velocity, and so on).

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Chapter 1

Release of flavors from spray-dried matrices takes place upon reconstitution of the dried emulsion in the release medium, water most often. Reasonable prediction of the release behavior should take into consideration the complex chemistry of flavors and the prevailing partition and phase transport mechanisms between aqueous and non-aqueous phases (Larbouss et al., 1991; Shimada et al., 1991). Encapsulation into an amorphous matrix via extrusion has gained wide popularity in the last two decades with applications ranging from entrapping flavors for their controlled release to masking the grittiness of minerals and vitamins. Hot melt extrusion is a highly integrated process with many unique advantages for encapsulation applications, namely: 1. Extruders are multifunctional systems (many unit operations) that can be manipulated to provide desired processing temperature and shear rate profiles by varying screw design, barrel heating, mixing speed, feed rate, moisture content, plasticizers, and so on. 2. Possibility of incorporating actives and other ingredients at different points of the extrusion process. Heat-labile actives, for example, can be incorporated via temperaturecontrolled inlets toward the end of the barrel and their residence time in the extruder can be minimized to avoid degradation of the active and to preserve its integrity. 3. Extruders are also formers—encapsulated products can be recovered in practically any desired shape or size (pellets, rods, ropes, and so on). 4. Only very limited amount of water is needed to transform carbohydrates from their native crystalline structure to amorphous glassy matrices in an extruder, thus limiting the need for expensive downstream drying. 5. High payload—up to 30% can be expected when encapsulating solid actives in extruded pellets. 6. Economics—attributes such as high throughput, continuous mode, and limited need for drying make extrusion a very attractive process for manufacturing encapsulated ingredients. Figure 1.2 describes a typical melt extrusion encapsulation process. Carbohydrate (encapsulating matrix), a mixture of sucrose and maltodextrin, is dry fed and melted by a combination of heat and shear in the extruder barrel so that the crystalline structure is transformed into an amorphous phase. The encapsulant (flavor or other active) is added through an opening in a cooled barrel situated toward the die to avoid flashing off of low boiling components. The amorphous mixture exits the die in the form of a rope that can be cooled quickly by air or liquid nitrogen to form a solid glassy material. The latter can be ground to a desired particle size to form compact microparticles of high bulk density. Using this technology, encapsulated products can be designed to achieve any desired target glass transition temperature by incorporating plasticizers (reduce Tg) or high-molecular weight polymers (increase Tg). It should be cautioned that although glass transition and associated microcapsule stability are clearly related to the material properties of the matrix and rates of crystallization, there is growing evidence that in the glass transition region small molecules are more mobile than might be expected from the high viscosity of the matrix (Parker and Ring, 1995). Mechanism of degradation of molecules entrapped in a glassy matrix is not fully understood but is speculated to be due to side-chain flexibility (e.g. enzymes) and/or diffusion of small molecules such as water and oxygen through the glassy matrix. Other deteriorative mechanisms may include Maillard reaction between the active and the carrier matrix.


Introduction

5

Active (powder, dispersion, emulsion)

Sugar blends (Dry feed)

Amorphous rope EXTRUDER Mixing & heating Ground microparticles Figure 1.2.

Encapsulation into amorphous carbohydrate matrices using hot melt extrusion.

Microcapsules manufactured via spray drying and extrusion may show structural imperfections, thus limiting their shelf life. While spray-dried microcapsules tend to have low bulk density, extruded granules may show stickiness and clumping. In addition, the presence of exposed active on the microparticle surface may have detrimental consequences such as drifts in the release profile and/or loss of active due to oxidation and other deteriorative processes. A limited number of applications have employed freeze drying or other evaporative techniques to form carbohydrate glasses from solution. Here, the removal of water molecules takes place either by freezing the solution and subliming the ice as in freeze drying or by evaporation. Freeze drying forms porous substrates due to transport of water vapor. Unlike starches, sugars lack fixed molecular structure; thus they collapse upon freeze drying. Co-crystallization with sugars has been practiced in few unique situations but has not found any commercial success. Crystalline sucrose is a poor flavor carrier but cocrystallization with flavors forms aggregates of very small crystals that incorporate the flavors either by inclusion within the crystals or by entrapment between them. Release of actives from amorphous carbohydrate matrices takes place by subjecting the matrix to moisture or high temperatures, that is, by bringing the matrix to a state above its glass transition temperature. Microcapsules entrapped in amorphous structures are preferred for their ease of manufacturing, scalability and economics compared to other encapsulation technologies. Their usage has been adapted to a variety of food systems such as surface sprinkle on breakfast cereals, hot instant drinks, soups, tea bags, chewing gum, pressed tablets, and so on.

Complexation of Actives into Cyclodextrins Entrapment of actives into cyclodextrins is a unique approach to microencapsulation that is based on molecular selectivity. Cyclodextrins are cyclic oligosaccharides formed of various numbers of α-(1,4) linked pyranose subunits. The 6-, 7-, and 8-numbered cyclic structures are referred to as α-, β-, and γ-cyclodextrins, respectively; these molecules vary in their solubility, cavity size, and complexation properties (Table 1.1).

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Chapter 1

Table 1.1. 2004)

Selected physicochemical properties of cyclodextrins (adapted from Martin Del Valle

Attribute Number of glucopyranose units Molecular weight (g/mol) Solubility in water at 25°C (% w/v) Cavity diameter (Å) Cavity volume (Å)3

-Cyclodextrin

-Cyclodextrin

-Cyclodextrin

6 972 14.5 4.7–5.3 174

7 1135 1.85 6.0–6.5 262

8 1297 23.2 7.5–8.3 427

Type and degree of complexation in cyclodextrins are determined by two main factors: (1) steric fit of the guest (encapsulant) to the host (cyclodextrin) and (2) their thermodynamic interactions, mainly hydrophobic type. Generally, one guest molecule is included in one cyclodextrin molecule, although for some molecules with low molecular weight, more than one guest molecule may fit into the cavity (Figure 1.3). For molecules with large hydrodynamic radii, more than one cyclodextrin molecule may bind to the guest. In principle, only a portion of the molecule must fit into the cavity to form a complex. As a result, one-to-one molar ratios are not always achieved, especially with high- or low-molecular-weight guests. Guest molecules in cyclodextrins are not permanently entrapped but occur in a dynamic equilibrium. However, once a complex is formed and dried, it is very stable and often results in very long shelf life (up to years at ambient temperatures under dry conditions). Release of the complexed guest takes place by immersing the guest-host complex in aqueous media to dissolve the complex and further promoting the release of the guest when displaced by water molecules. A wide variety of molecules can be entrapped in cyclodextrins such as fats, flavors, colors, and so on (Martin Del Valle, 2004; Parrish, 1988). Complexation of cyclodextrins with

Figure 1.3.

Schematic representation of a molecule entrapped in cyclodextrins.


Introduction

7

sweetening agents such as aspartame can also stabilize the molecule and improve its taste as well as eliminate the bitter aftertaste of other sweeteners such as stevioside and glycyrrhizin. Cyclodextrins can entrap undesirable substances such as cholesterol from products such as milk, butter, and eggs (Szetjli, 1998; Hedges, 1998).

Encapsulation in Microporous Matrices—Physical Adsorption Physical adsorption can only be feasible when an active is adsorbed onto a large surface area, microporous substrate, commonly referred to as molecular sieve. Examples of this category include activated carbon (500–1400 m2/g) and amorphous silica (100–1000 m2/g) (Cheremisinoff and Morresi, 1978). Despite their efficiency in entrapping volatiles, silica and activated carbon usage in foods has been discouraged due to regulatory constraints and is currently limited to packaging applications. The effectiveness of these materials is demonstrated by extensive reduction in equilibrium vapor pressure which accompanies physical adsorption of volatile flavors. Micronized sugars have been used but with limited success in adsorption applications. Dipping capillary-sized droplets of sucrose or lactose solution into liquid nitrogen followed by freeze drying can produce amorphous spheres that have the ability to adsorb aromas. Sorption of vapor causes these materials to revert to the more stable crystalline state with accompanying loss of porosity.

Encapsulation in Fat- or Wax-Based Matrices Entrapment of functional actives in fat-based matrices can be achieved using two main technologies, hot-melt fluid bed coating and spray congealing. Actives can best be entrapped via mixing them with a fat/wax carrier followed by spray congealing. These technologies have been adequately discussed in Chapter 5 which deals with the encapsulation of bakery leavening agents.

Encapsulation in Emulsions and Micellar Systems Encapsulation via micelles is a convenient approach to enhance the solubility of insoluble or slightly soluble actives. This technique involves the simple entrapment of a hydrophobic active in a hydrophilic shell material, thus rendering the particle or droplet soluble in aqueous media. This is no trivial matter when considering the problems with bioavailability of hydrophobic drugs and nutritional actives (fat-soluble vitamins, fish oil, and a host of water-insoluble drug actives). A second important function of micelles is their small size which allows them to evade the body’s screening mechanism, the reticuloendothelial system (RES). Recognition by RES is the main reason for removal of many drug delivery vehicles from the blood before reaching their target site (Sagalowicz et al., 2006). Micelles serve as drug “reservoirs” or “microcontainers” that ultimately release drugs via diffusional processes. An in-depth discussion on encapsulation into emulsion systems can be found in Chapters 2 and 3 of this book by Professor Garti and Dr. Zuidam and their respective coworkers.

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Chapter 1

Encapsulation in Cross-Linked or Coacervated Polymers Coacervation, as defined by Speiser (1976), is a process of transferring macromolecules with film properties from a solvated state via an intermediate phase, the coacervation phase, into a phase in which a film is formed around each particle and then to a final phase in which this film is solidified or hardened. Two types of coacervation processes are commonly used in encapsulation applications, namely simple and complex: 1. Simple coacervation is based on “salting out” of one polymer by addition of agents (salts, alcohols) that have higher affinity to water than the polymer. It is essentially a dehydration process whereby separation of the liquid phase results in the solid particles or oil droplets becoming coated and eventually hardened into microcapsules. 2. Complex coacervation, on the other hand, is a process whereby a polyelectrolyte complex is formed. It requires the mixing of two colloids at a pH at which one is negatively charged and the other positively charged, leading to phase separation and formation of enclosed solid particles or liquid droplets (Rabiskova and Valaskova, 1998). Several parameters can impact the formation and integrity of coacervates such as the polymers’ molecular weight, their w/w ratios, temperature, and processing time. Core materials suitable for coacervation are solids and liquids that are water-insoluble so that the active would not dissolve in the aqueous phase. One of the approaches to achieving high oil payloads is by using hydrophobic surfactants (Rabiskova and Valeskova, 1998). The release of actives from coacervated systems is primarily a function of the wall type and its thickness (slower release with increased wall thickness). Chapter 7 of this book presents an in-depth discussion on coacervation for flavor encapsulation applications.

Encapsulation into Hydrogel Matrices Hydrogels are hydrophilic, three-dimensional network gels that can absorb much more water than their own weight. Hydrogels consist of (a) polymers, (b) molecular linkers or spacers, and (c) an aqueous solution. Basic high-molecular-weight polymers include polysaccharides, proteins, chitin, chitosans, hydrophilic polymers, and so on (Shahidi et al., 2006). The affinity of hydrogels to aqueous media makes them ideal absorbing matrices for food and agricultural actives. The principle of encapsulation by hydrogels is simply to entrap an active substance and to further release it via gel-phase changes in response to external stimuli. Grahm and Mao (1996) categorized the types of materials that cannot be delivered via hydrogels as: (i) extremely water-soluble actives due to the risk of uncontrollable quick release and (ii) very high-molecular-weight substances due to the extremely slow release rate to achieve a desired benefit. Release of actives from hydrogels takes place via diffusion. The latter can be impacted by various chemical and physical factors such as the prevailing chemical bonds (H-bonds, ionic bonds, electrostatic interactions, and hydrophobic interactions) between the active and the matrix. Physical factors include molecular size and conformation. Controlling (extending) the release of an active in a hydrogel matrix can be achieved by decreasing the hydrophilicity and/or diffusivity of the hydrogel structure or by covalently linking the active to the carrier hydrogel matrix.


Introduction

9

Ideal hydrogels display a sharp phase transition upon swelling in an aqueous solvent in response to environmental stimuli such as temperature, pH, electric field, and so on. Release from hydrogels can be predicted from their LCT (lower critical solution temperatures) values. As temperature increases to the hydrogel’s LCT, the hydrogel shrinks due to dehydration. Below LCT, hydrogels can take up water thus increasing their swelling (Ichikawa et al., 1996).

Overview of Release Mechanisms Despite the far-reaching applications of encapsulation and controlled-release technologies in many industries, predicting the release of encapsulated actives, especially in biological systems (foods included), remains a challenge. In the human gastrointestinal tract (GIT), for example, the release of microcapsules is a function of the physiological conditions, presence of food as well as the physicochemical properties of the ingested dosage. One of the essential requirements for predicting release mechanisms of microencapsulated dosages is by identifying parameters involved in mass transport and diffusion of the actives from a region of high concentration (dosage) to a region of low concentration in the surrounding environment. Encapsulation and controlled-release systems can be classified into two main types: reservoir and matrix systems and, in some cases, combinations of both.

Reservoir-Type Systems Reservoir-type systems are simply described as delivery devices where an inert membrane surrounds an active agent which upon activation diffuses through the membrane at a finite controllable rate (Figure 1.4a). Reservoir-type systems are capable of achieving zero-order rates provided that constant thermodynamic activity is maintained inside the coating material. Reservoir-type systems are subject to shifts to a “burst-like” mechanism due to minor flaws in the membrane integrity.

Matrix Systems Matrix or monolithic delivery systems can best be represented by microparticles prepared by extrusion or fat-congealed capsules where the actives are dispersed in the encapsulating

(a) Reservoir-type device

(b) Matrix-type device

(c) Combination-type device

Figure 1.4. Schematic representation of encapsulation systems: (a) reservoir-type, (b) matrix-type, and (c) combination-type.

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Chapter 1

medium (carbohydrate, fat, or other matrices). Matrix systems can be swellable (hydrogel) or non-swellable. Compared to reservoir systems, matrix systems require less quality control, hence lower manufacturing cost (Figure 1.4b).

Combination Release Mechanism Examples of this category can best be illustrated by congealed microcapsules or extruded microparticles with additional film. coating (enrobing). This technique is most useful for manufacturing extremely “delayed release” profiles (Figure 1.4c).

Burst Release Mechanism Burst release is simply described by a high initial delivery of an entrapped active, before the release reaches a stable profile, thus reducing the system’s effective lifetime and complicating the release control. Although burst release may be preferred for flavor highimpact applications, in drugs this mechanism may lead to high toxicity levels and ineffective administration of the active. Burst release can most often take place in reservoir and hydrogel systems, though it can still take place in matrix designs. Reasons for this range from cracks in the protective capsule shell to storage effect where the membrane becomes saturated with the active substances or due to very high active loading. When placed in a release medium, the active can quickly diffuse out of the membrane surface causing a burst effect (Huang and Brazel, 2001). Low-molecular-weight actives frequently undergo burst release, a result of high osmotic pressure and increased concentration gradient. Other reasons include: processing conditions, surface characteristics of host material, sample geometry, host/drug interactions, morphology, and porous structure of dry material. Application of a coating material over a monolithic microparticle can help eliminate burst release, though might change the release profile. Other treatments include washing microparticles to extract surface droplets of actives.

First-order Brust release

Figure 1.5.

Zero-order

Release rates (zero-order, first-order, and burst) of microencapsulated systems.


Introduction

11

Kinetically, two main release patterns are identified, zero-order and first-order (Figure 1.5). Other rates can still occur: Zero-order release equation First-order release equation

–dA/dt = k –dA/dt = k[C]

where –dA/dt is the change in active concentration over time, k is the rate constant, and [C] is the active’s concentration. In designing microcapsules with controlled-release systems, it is critical to identify desirable release profile so that adequate materials and technology can be chosen.

References Baker, R.W. and Lonsdale, H.K. 1974. Controlled release: mechanisms and rates. In: Controlled Release of Biologically Active Agents (A.C. Tanquary and R.E. Lacey, eds.), Plenum, New York, pp. 15–71. Cheremisinoff, P.N. and Morresi, A.C. 1978. Carbon adsorption applications. In: Carbon Adsorption Handbook (P.N. Cheremisinoff and F. Ellerbusch, eds.), Ann Arbor Science Publishers, Inc., Ann Arbor, Michigan, p. 3. Conde-Petit, B., Escher, F. and Nuessli, J. 2006. Structural features of starch-flavor complexation in food model systems. Trends in Food Science & Technology 17(5): 227–235. Grahm, N.B. and Mao, J. 1996. Controlled drug release using hydrogels based on poly(ethylene glycols): macrogels and microgels, pp. 52–64. In: Chemical aspects of Drug Delivery, Karsa, D. and Stephenson, R. (Eds). Royal Society of Chemistry. Hedges, R.A. 1998. Industrial applications of cyclodextrins. Chem. Rev. 98: 2035–2044. Huang, X. and Brazel, C.S. (2001). On the importance and mechanisms of burst release I matrix-controlled drug delivery systems. J. Controlled Release 73: 121–136. Ichikawa, H., Kaneko, S. and Fukumori, Y. 1996. Coating performance of aqueous composite lattices with N-ispropylacrylamide shell and thermosensitive permeation properties of their microcapsule membrane. Chem. Pharm. Bull. 44(2): 383–391. Larbousse, S., Roos, Y. and Karel, M. 1992. Collapse and crystallization in amorphous matrices with encapsulated compounds. Sci. Aliments 12: 757–769. Martin Del Valle, E.M. 2004. Cyclodextrins and their uses: a review. Process Biochem. 39: 1033–1046. Masters, K. 1979. Spray Drying Handbook, 3rd ed., George Godwinn, London. Parrish, M.A. 1988. Cyclodextrins—A Review. England: Sterling Organics. Newcastle-upon-Tyne NE3 3TT. Parker, R. and Ring, S.G. 1995. Diffusion in maltose-water mixtures at temperatures close to the glass transition. Carbohydr. Res. 273: 147–155. Rabiskova, M. and Valaskova, J. 1998. The influence of HLB on the encapsulation of oils by complex coacervation. J. Microencapsul. 15(6): 747–751. Sagalowicz, L., Leser, M.E., Watzke, H.J. and Michel, M. 2006. Monoglyceride self-assembly structures as delivery vehicles. Trends in Food Science & Technology 17(5): 204–214. Shahidi, F., Arachchi, J.K.V. and Jeon, Y.-J. 2006. Food applications of chitin and chitosans. Trends in Food Science & Technology 10(2): 37–51. Shimada, Y., Roos, Y. and Karel, M. 1991. Oxidation of methyl linoleate encapsulated in amorphous lactose-based food model. J. Agric. Food Chem. 39: 637–641. Speiser, P. 1976. Microencapsulation by coacervation, spray encapsulation and nanoencapsulation. In: Microencapsulation, Nixon, J.R. (Ed.), pp. 1–11. Szetjli, J. 1998. Introduction and general overview of cyclodextrin chemistry. Chem. Rev. 98: 1743–1753.

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Improved Solubilization and Bioavailability of Nutraceuticals in Nanosized Self-Assembled Liquid Vehicles Nissim Garti, Eli Pinthus, Abraham Aserin, and Aviram Spernath

Introduction Microemulsions have been known for decades to the scientific community and to experts in the industry. Hundreds of studies have been carried out by experimentalists and many theories have been worked out regarding the self-aggregation of surfactants in aqueous phase as well as in oil phase, to form micellar or reverse micellar (respectively) structures. The micellar phases can be swollen by another liquid phase to form a reservoir of insoluble liquid phase entrapped by a tightly packed surfactant layer known as water-in-oil (w/o) or oilin-water (o/w) microemulsions. Microemulsion, by the most common general definition, is a “structured fluid” (or solution-like mixture) of two immiscible liquid phases in the presence of a surfactant (sometimes with cosurfactant and cosolvent), which spontaneously form a thermodynamically stable isotropic solution-like liquid. In spite of the numerous studies and pronounced potential applications in foods, pharmaceuticals, and cosmetics, only a few practical preparations, in which the solubilized molecules are at very low solubilization levels, are presently available in the market place. It is always an open question as to why these structures did not make their way to final products. The self-assembled nanosized surfactants and oil can solubilize another liquid immiscible phase and/or guest molecules (solubilizates). Droplet sizes are in the range of a few up to a hundred nanometers. In theory, in order to form such nanostructures, it is essential to reduce the interfacial tension between the two phases to a value close to zero. In order to do so, surfactants with the proper hydrophilicity must be utilized. In addition, surfactants must have the proper geometry to self-organize in curved structures with the proper critical packing parameters (CPP). Microemulsions are best studied by constructing binary, ternary, or multicomponent phase diagrams, which represent the equilibrium situation of the component mixture or the thermodynamic organization of the components. A typical classical phase diagram is shown in Figure 2.1. Understanding the phase behavior and microstructure of microemulsions is an important fundamental aspect of the utilization of these structured fluids in industrial applications. Today, we have a more profound understanding of the phase behavior and microstructure of microemulsions (Shinoda and Lindman, 1987; Billman and Kaler, 1991; Kahlweit et al., 1996; Regev et al., 1996; Solans et al., 1997; Ezrahi et al., 1999). However, industrial applications of microemulsions are rarely simple ternary systems, but more often complicated multicomponent systems. It is not always clear whether, in the complex systems, droplet

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Chapter 2

Figure 2.1. Typical phase diagram made with water, emulsifiers, and oil phase. Four types of isotropic regions have been identified. Note that the dilution lines traverse via a two-phase region and full dilution to the far corner of the water phase is not possible.

sizes and shapes are similar and remain intact and the role of the different components in stabilizing the interface. Systematic investigations should be carried out to understand the microstructure and the effect of the different components on the system. In recent years, few attempts have been made to formulate and characterize microemulsions that can be used for food, cosmetic, and pharmaceutical purposes (Dungan, 1997; Gasco, 1997). In this effort, oils acceptable in food industry have replaced normal alkanes. The majority of easily made preparations were of oil-continuous phase (w/o). The authors focused on studying the ability of formulating a microemulsion with triglycerides (Alander and Warnheim, 1989a, b; Malcolmson and Lawrence, 1995; von Corswant et al., 1997; von Corswant and Söderman, 1998; Warisnoicharoen et al., 2000) and perfumes (Hamdan et al., 1995; Tokuoka et al., 1995; Kanei et al., 1999) as the oil component. Some workers (Joubran et al., 1993; Trevino et al., 1998) have studied the phase behavior and microstructure of water-in-triglyceride (w/o) microemulsions based on polyoxyethylene sorbitan hexaoleate. They found that the monophasic area of these systems was strongly dependent on temperature and aqueous phase content. In other studies, o/w microemulsions were used. Lawrence and coworkers (Malcolmson and Lawrence, 1995; Warisnoicharoen et al., 2000) examined the solubilization of a range of triglycerides and ethyl esters in an o/w microemulsion system


Improved Solubilization and Bioavailability of Nutraceuticals

15

with nonionic surfactants. They concluded that the solubilization capacity depends not only on the nature of the surfactants but also on the nature of the oil. There are very few surfactants that can be used in food formulations. In this respect, polysorbates (Tweens, ethoxylated derivatives of sorbitan esters) and sugar esters are interesting families of surfactants. The substitution of the hydroxyl groups on the sorbitan ring with bulky polyoxyethylene groups increases the hydrophilicity of the surfactant. Similarly, monoesterification of sucrose forms hydrophilic emulsifiers. The ability of Tweens to form microemulsions for food applications has been studied by several authors (Constantinides and Scalart, 1997; Trotta et al., 1997; Park and Kim, 1999; Prichanont et al., 2000; Radomska and Dobrucki, 2000). An increased solubility of lipophilic drugs in the microemulsion region was observed and explained by the penetration of these drugs into the interfacial film (Trotta et al., 1997; Park and Kim, 1999; Radomska and Dobrucki, 2000). Even though some food-grade emulsifiers have been mentioned as possible microemulsion-forming amphiphiles, it was almost impossible to use these systems mainly because the concentrates of oil/surfactant mixtures could not be fully diluted with water or aqueous phases to form o/w microemulsions. Any such dilution line (composition) is always “crossing” the two-phase region, resulting in a fast destabilization process and formation of emulsions or two phases. Such phase separation leads to rapid precipitation of the solubilized matter. Some examples of such discontinued dilution lines illustrate the dilution problem of the classical phase diagrams. In Figure 2.1, these dilution lines are marked as dashed lines. In most studies, the emphasis was on attempts to add just one immiscible liquid such as water (or oil) to the oil (or water)-continuous surfactant phase, that is, to solubilize the oil in the core (inner phase) of the micelles. Practically very few attempts were made to incorporate additional guest molecules, such as vitamins, aromas, antioxidants, and bioactive molecules, into the solubilized core. Very little has been done to solubilize nutraceuticals within nanosized liquid vehicles in order to provide some pronounced health benefits to humans or to treat chronic diseases. Many structural and compositional limitations, in the presently available food formulations, did not permit loading significant amounts of nutraceuticals. It is not an easy task to accomplish, since there is a need for additional technology to be developed. It is essential to introduce new ingredients, new surfactants, and new concepts in microemulsion preparation. Some of the cardinal points to be solved include the following: • Progressively and continuously diluting, by aqueous phase or water, without destroying the interface and forming two-phase regions, that is, forming the so-called U-type phase diagrams that undergo progressive inversion from w/o to o/w microemulsions (Figure 2.2). • Preparing microemulsions that will be based on the use of permitted food-grade emulsifiers, oils, cosurfactants, or cosolvents. • Facilitating the entrapment (cosolubilization capacity) of large loads of insoluble guest molecules within the core of the microemulsion or at its interface. • Providing environmental protection of the active addenda (guest molecules) from autooxidation or hydrolytic degradation during shelf storage. • Improving the bioavailability of the entrapped addenda. • Controlling the release from the vehicle to the water-continuous phase or onto human membranes. • Using microemulsions as microreactors to obtain regioselectivity, fast kinetics, and controlled and triggered reactions of active molecules once applied on the skin.

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Chapter 2

Figure 2.2. Typical novel U-type phase diagram composed of selected combinations of cosmetic-grade emulsifiers with progressive full dilution.

A phase diagram with a very large isotropic one-phase region is typical of the novel microemulsions that are made from multicomponents. The isotropic regions represent w/o, bicontinuous mesophase, and o/w microemulsion structures. The phase diagrams are known as U-type. In such compositions, within the isotropic regions of the phase diagram, the oil/surfactant condensed structured mixtures (denoted condensed reverse micelles, L2) can transform to an L1 phase (direct micelles) via a w/o microemulsion, bicontinuous mesophase, and o/w microemulsion regions progressively, without any phase separation. To the best of our knowledge, no reports were available in the literature, prior to the establishment of our formulations as part of the extended new U-type phase diagrams, to comply with these prerequisites of dilutable large isotropic regions (Garti et al., 2001, 2003, 2004a, b; Yaghmur et al., 2002a, b, c, 2003a, b, 2004, 2005; Spernath et al., 2002, 2003; de Campo et al., 2004). Most of the early studies were conducted on systems with constant water content (>70%), low oil content (ca. 5–10%), and large surfactant excess (high surfactant/oil ratios). We enlarged the scope of the understanding and use of such microemulsions to food and cosmetic preparations. Our studies examined various aspects of solubilization of nutraceuticals, release patterns, and other thermal and environmental conditions. In some of our studies the role of the surfactant was examined. The maximum solubilization load was determined, and efforts were made to estimate the total amounts of active matter that can be entrapped along any dilution line. We were the first to establish the correlation between maximum solubilization capacity and water dilution (Garti et al., 2001, 2003, 2004; Spernath et al., 2002, 2003; Yaghmur et al., 2002a, b, c , 2003a, b, 2004, 2005; de Campo et al., 2004). This review summarizes our efforts to develop modified microemulsions as nanosized self-assembled liquid (NSSL) vehicles for the solubilization of nutraceuticals and to improve transmembrane transport for additional health benefits. Attempts were made to achieve solubilization of nonsoluble active ingredients such as aromas and antioxidants into clear beverages that are based on water-continuous phase.



17

U-Type Microemulsions, Swollen Micelles, and Progressive and Full Dilution Initially we (Garti et al., 2001; Yaghmur et al., 2002a, b) dealt with solubilization of water and oil in the presence of a new set of nonionic ingredients and emulsifiers to form U-type nonionic w/o and o/w food microemulsion systems. It was recognized that certain molecules destabilize the liquid crystalline phases and extend the isotropic region to higher surfactant concentrations. The ability of these additives to provide large monophasic systems (denoted as the AT region in Figure 2.2), in which the total amounts of solubilized oil and water should be as high as possible, was studied. The pseudoternary phase diagrams for R(+)-limonene-based systems with food-grade systems were compared with those based on non-food grade emulsifiers such as Brij 96v, (C18:1(EO)10, Figure 2.2) (Garti et al., 2001; Yaghmur et al., 2002b). These systems offer great potential in practical formulations. We followed the structural evolution and transformation of the microemulsion system from aqueous phase-poor to aqueous phase-rich regions without encountering phase separation. Figure 2.3a demonstrates the size distribution of various droplets along dilution line 73 (D73; 70 wt% surfactant and 30 wt% oil phase) from 10 to about 90 wt% water. It can be seen that the droplets in the w/o region are smaller than those at higher water content upon inversion to o/w microemulsions. Figure 2.3b represents a typical structure as seen in the cryo-TEM (transmission electron microscopy) photomicrographs of an o/w microemulsion taken from the rich-in-water region of the U-type diagram (obtained after inversion from an L2 phase into o/w droplets upon dilution with aqueous phase to 90 wt% water). The droplet sizes are ca. 8–10 nm and are mostly monodispersed. It should be noted that most microemulsions, regardless of the type of oil, type of surfactant, and cosolvents, consist of droplets of ca. 5–20 nm in size and do not grow above these sizes at any water or oil contents. Various U-type phase diagrams with different types of hydrophilic surfactants, various cosolvents, and cosurfactants were constructed to form small or large isotropic AT regions. The most desirable phase diagram yielded an isotropic region of AT > 75% from the total area of the phase diagram. The dilution lines connecting the oil/surfactant axis with the water corner were termed Wm lines. Full dilution lines are those that can undergo full and progressive dilution to the far water corner (Wm = 100%). Wm = 50% means that samples can be diluted only up to 50 wt% water and if more water is added the microemulsion will undergo phase separation. An example of Wm = 100% dilution line is line 64 in Figure 2.2, in which a mixture of 60 wt% surfactant phase and 40 wt% oil phase is diluted progressively and completely with aqueous phase to the far corner (Wm = 100%) aqueous phase. In dilution line 55 (50 wt% surfactant phase and 50 wt% oil phase), the Wm is of ca. 60% aqueous phase, and further dilution will lead to phase separation. Construction of U-type phase diagrams is essential for formulations of water-dilutable microemulsions.

Solubilization of Nonsoluble Nutraceuticals The growing interest in microemulsions as vehicles for food and cosmetic formulations arises mainly from the advantages of their physicochemical properties. Microemulsions can cosolubilize large amounts of lipophilic and hydrophilic nutraceutical and cosmetoceutical additives, together with the inner reservoir.

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Normalized to 1 at the maximum

(a)

10% AP

1

30% AP 40% AP 50% AP 60% AP 70% AP

p(r ) [a.u.]

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Chapter 2

80% AP 90% AP

0 0

2

4

6

8

10

12

14

16

18

r [nm] (b)

Figure 2.3. (a) Droplet size distribution of various dilution points along dilution line 73 in phase diagram depicted in Figure 2.2. (b) Photomicrograph of typical o/w droplets derived from a concentrate of w/o after dilution to 90 wt% water content (AP refers to aqueous phase). (Adapted from Garti, with permission from the publisher.)

The cosolubilization effect has attracted the attention of scientists and technologists for more than two decades. Oil-in-water microemulsions loaded with active molecules opened new prospective opportunities for enhancing the solubility of hydrophobic vitamins, antioxidants, and other skin nutrients. This is of particular interest, as it can provide a well-controlled way for incorporating active ingredients and may protect the solubilized components from undesired degradation reactions (Garti et al., 2001; Spernath et al., 2002; Yaghmur et al., 2002a, b, c). Figure 2.4 is a schematic illustration of the loading process of various nutraceuticals onto the o/w microemulsion droplets after inversion. Solubilization of active addenda may, therefore, be defined as spontaneous molecular entrapment of an immiscible substance (or only slightly miscible or soluble) in selfassembled surfactant mixtures to form a thermodynamically stable, isotropic, structured solution, consisting of nanosized liquid structures.



19

Figure 2.4. A schematic illustration of the loading process of various nutraceuticals onto the o/w microemulsion droplets after inversion. (Adapted from Nutralease and Garti, 2003, with permission from the publisher.)

The solubilized active molecules are compounds with nutritional value to human health that, in most cases, are used in food applications. We will mention a few such examples that were studied in our labs, such as lycopene, phytosterols, lutein, tocopherols, CoQ10, and essential oils.

Lycopene Food supplements have become very prominent compounds in recent years, due to increased public awareness of healthy nutrition. The possibility of enhancing the solubility of lipophilic vitamins, essential oils, aromas, flavors, and other nutrients in o/w microemulsions is of great interest, as it can provide a well-controlled method for the incorporation of active ingredients and may protect the solubilized components from undesired degradation reactions (Dungan, 1997; Holmberg, 1998; Garti et al., 2000a, b). Lycopene (Figure 2.5) is an important carotenoid that imparts a characteristic red color to tomatoes. This lipophilic compound is insoluble in water and in most food-grade oils. For example, lycopene solubility in one of the most efficient edible essential oils, R(+)-limonene, is 700 ppm. Recent studies have indicated the important role of lycopene in reducing risk factors of chronic diseases such as cancer, coronary heart disease, and premature aging (Dungan, 1997; Holmberg, 1998). This, in turn, has led to the idea of studying the effect of lycopene uptake on human health.

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Chapter 2

Figure 2.5.

Molecular structure of lycopene.

Bioavailability of lycopene is affected by several factors: • Food matrix containing the lycopene and, as a result, intracellular location of the lycopene, and the intactness of the cellular matrix. Tomatoes converted into tomato paste can enhance the bioavailability of lycopene, as the processing includes mechanical particle size reduction and heat treatment. • Amount and type of dietary fat present in the intestine. The presence of fat affects the formation of the micelles that incorporate the free lycopene. • Interactions between carotenoids that may reduce absorption of either one of the carotenoids (Bramley, 2000) owing to competitive absorption between the carotenoids. On the other hand, simultaneous ingestion of various carotenoids may induce antioxidant activity in the intestinal tract, and thus result in increased absorption of the carotenoids (Rao and Agrawal, 1999; Bramley, 2000). • Molecular configuration (cis/trans) of the lycopene molecules. The bioavailability of the cis isomer is higher than the bioavailability of the trans isomer. This may result from the greater solubility of cis isomers in mixed micelles and lower tendency of cis isomers to aggregate (Cooke, 1998; Rao and Agrawal, 1999). • Decrease in particle size (Van het Hof et al., 2000). Care must be taken in formulating lycopene as an additive in food systems, since the large number of conjugated bonds in this carotenoid causes instability when exposed to light or oxygen. We explored the ability of U-type microemulsions to solubilize lycopene and have also investigated the influence of solubilized lycopene on the microemulsion microstructure. Phase diagrams have been constructed, lycopene has been solubilized, and several structural methods have been utilized including self-diffusion nuclear magnetic resonance (SD-NMR) spectroscopy. This advanced analytical technology was further developed to determine the microemulsion microstructure at any dilution point. The influence of microemulsion composition on the solubilization of lycopene in a fivecomponent system consisting of R(+)-limonene, cosurfactant, water, cosolvent, and polyoxyethylene (20) sorbitan mono-fatty esters (Tweens) is presented in Figures 2.6 and 2.7. Solubilization capacity was defined (Spernath et al., 2002, 2003) as the quantity of lycopene solubilized in the microemulsion. Figure 2.7 shows the solubilization capacity of lycopene along water dilution line T64 (at this line the constant ratio of R(+)-limonene/ ethanol/Tween 60 is 1/1/3, respectively). Four different regions can be identified along this dilution line. At 0–20 wt% aqueous phase (region Ι), the solubilization capacity of lycopene decreases dramatically, from 500 to 190 ppm (reduction of 62%). This dramatic decrease in the solubilization capacity can be associated with the increase in interactions between the surfactant and water molecules. Water can also strongly bind to the hydroxyl



21

Figure 2.6. Pseudoternary phase diagram (25ºC) of water/PG/R()-limonene/ethanol/Tween 60 system with a constant weight ratio of water/PG (1:1) and a constant weight ratio of R()limonene/ethanol (1:1). Solubilization of lycopene was studied along dilution line T64. (Adapted from Yaghmur and Garti, 2001, with permission from the publisher.)

Figure 2.7. Solubilization capacity of lycopene along dilution line T64 as per phase diagram in Figure 2.6. (Adapted from Garti, with permission from the publisher.)

groups of the surfactant at the interface. When water is introduced to the core, the micelles swell, and more surfactant and co-surfactant participate at the interface, replacing the lycopene, thus decreasing its solubilization. In region Ι, the reverse micelles swell gradually and become more hydrophobic, causing less free available volume for the solubilized lipophilic lycopene and a reduction in its solubilization capacity. At 20–50 wt% aqueous phase (region II) the solubilization capacity remains almost unchanged (decreases only by an additional 7%). This fairly small decrease in the solubilization capacity could be associated with the fact that the system transforms gradually into a bicontinuous phase and the interfacial area remains almost unchanged when the aqueous phase concentration increases. Surprisingly, in region ΙΙΙ (50–67 wt% aqueous phase) the solubilization capacity increases

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22

1.000

1.000

0.100

0.000

0.010

0.010

0.001 0

(b)

20 40 60 80 Aqueous phase (wt%)

0.001 100

1.000

1.000

0.100

0.000

0.010

0.010

0.001 0

20 40 60 80 Aqueous phase (wt%)

D O/D0O

D W/D0W

(a)

D O/D0O

from 160 to 450 ppm (an increase of 180%). In region IV the solubilization capacity decreases to 312 ppm (a decrease of 30%). In order to explain the changes in solubilization capacity of lycopene, we characterized the microstructure of microemulsions along dilution line T64 using the SD-NMR technique. Figure 2.8 shows the relative diffusion coefficients of water and R(+)-limonene in empty (containing no solubilizates) microemulsions (Figure 2.8a) and microemulsions solubilizing lycopene (Figure 2.8b), as a function of the aqueous phase concentration (w/w). One can clearly see that the general diffusion coefficient behavior of microemulsion ingredients (R(+)-limonene and water), with or without lycopene, is not very different. The total amount of lycopene does not cause dramatic changes in the diffusion patterns of the ingredients. It can also be seen that, in the two extremes of aqueous phase concentrations (up to 20 wt% and above 70–80 wt% aqueous phase), the diffusion coefficients are easily interpreted, while the regions in between are somewhat more difficult to explain, since gradual

D W/D0W

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Chapter 2

0.001 100

Figure 2.8. Relative diffusion coefficient of water (•) and R()-limonene (▲) in microemulsions without (a) and with (b) lycopene, as calculated from SD-NMR results at 25ºC. D0w was measured in a solution containing water/PG (1:1), and determined to be 55.510–11 m2 s–1. D0o the pure diffusion coefficient of R()-limonene was determined to be 38.310–11m2 s–1. (Adapted from Garti, with permission from the publisher.)



23

changes take place. Regions ΙΙ and ΙΙΙ are difficult to distinguish. However, the structural changes in the presence of lycopene (Figure 2.8b) are more pronounced than those in the absence of lycopene (Figure 2.8a). Microemulsions containing up to 20 wt% aqueous phase, and solubilizing lycopene, have a discrete w/o microstructure, since the relative diffusion coefficients of water and R(+)-limonene differ by more than one order of magnitude. Microemulsions solubilizing lycopene and containing 20–50 wt% aqueous phase have a bicontinuous microstructure, as the diffusion coefficients of water and R(+)-limonene are of the same order of magnitude. Increasing the aqueous phase concentration to above 50 wt% induces the formation of discrete o/w microstructures, as the relative diffusion coefficients of water and R(+)-limonene differ by more than one order of magnitude. From the solubilization capacity and SD-NMR results, it is clear that lycopene solubilization is structure dependent. The four different regions in the solubilization capacity curve are an indication of the microstructure transition along the dilution line. The first region indicates the formation of w/o (L2) microstructure. The second region indicates the transition from L2 microstructure to a bicontinuous microemulsion. In the third region, a transition from a bicontinuous microemulsion to an o/w (L1) microstructure occurs. In the fourth region a discrete L1 microstructure was found. While the general behavior of the diffusion coefficients is the same for microemulsions with or without lycopene, the transition point from one microstructure to another is different. Lycopene influences the transition from L2 to bicontinuous microstructure and further to L1 microstructure. In empty microemulsions the formation of bicontinuous microstructure occurs when the microemulsion contains 40–60 wt% aqueous phase, whereas in a microemulsion containing lycopene, bicontinuous microstructure starts at low aqueous phase content (20 wt%) and continues up to an aqueous phase content of 50 wt%. It seems that as more water is solubilized in the swollen reverse micelles less free interfacial volume is available for the lycopene. Lycopene appears to disturb both the flexibility of the micelle and the spontaneous curvature. As a result, the interface changes into a flatter curvature (bicontinuous) at an early stage of water concentration, more so in the presence of lycopene than empty micelles. The hydrophilic–lipophilic balance (HLB) of the surfactant influences the quantity of solubilized lycopene in the aqueous surfactant phase. Tween 60, being a hydrophilic surfactant with the lowest HLB value (HLB 14.9), solubilizes 10 wt% more lycopene than Tween 80 (HLB 15.2). In Tween 40 (polyoxyethylene sorbitan monomyristate)-based microemulsions, the solubilization capacity drops even further (30%). Replacing Tween 60 with Tween 20, the most hydrophilic surfactant (HLB 16.7), reduces the solubilization capacity of lycopene by 88%. We have also demonstrated that microemulsions stabilized by mixed surfactants enhance the solubilization capacity of lycopene by 32–48%, in comparison to microemulsions stabilized by Tween 60 alone (Spernath et al., 2002; Garti et al., 2003, 2007), indicating a synergistic effect. Microemulsions stabilized by a mixture of three surfactants—Tween 60, sucrose ester, and ethoxylated monodiglyceride—have the highest solubilization capacity of lycopene—an increase of 48%, in comparison to microemulsion based on Tween 60 alone (Spernath et al., 2002; Garti et al., 2003, 2004a, b). Synergism in surfactant mixtures was attributed to Coulombic, ion-dipole, or hydrogen-bonding interaction (Hou and Shah, 1987; Huibers and Shah, 1997). Therefore, nonionic surfactant mixtures are expected to have a

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Chapter 2

minimum intermolecular interaction and weak synergistic effects. Nevertheless, Huibers and Shah (1997) demonstrated a strong synergism in nonionic surfactant mixtures, similar to the findings in our study. This behavior remains to be explained. Solubilization capacity is defined as the quantity (mg) of solubilizate entrapped in 100 g microemulsion, and solubilization efficiency is the quantity of solubilizate per 100 g of the oil phase or that normalized to oil content solubilization. Solubilization efficacy is the ratio of the quantity of solubilized compound to the quantity of the total amounts of oil and surfactant phase. Microemulsions exhibit very large solubilization capacities and solubilization efficiencies for lycopene. Lycopene was solubilized in a microemulsion up to 10 times its dissolution capacity in R(+)-limonene or in any other edible solvent. The solubilization capacity and efficiency of lycopene are strongly affected by microstructure transitions from w/o to bicontinuous and from bicontinuous to o/w. Solubilization capacity drops significantly with dilution, while the efficiency and efficacy increase as the water content increases, indicating that the interface plays a significant role in the solubilization of lycopene.

Phytosterols Elevated serum cholesterol level is a well-known risk factor for coronary heart disease (Hicks and Moreau, 2001). Most strategies for lowering serum cholesterol require dietary restrictions and/or medications. The prospect of lowering cholesterol levels by consuming foods fortified with natural phytonutrients is considered much more attractive. Phytosterols (plant sterols) are steroid alcohols. Their chemical structure resembles human cholesterol, as can be seen in Figure 2.9. Both sterols are made up of a tetracyclic cyclopenta[α]phenanthrene ring system and a long flexible side chain at the C17 carbon atom. The four rings have trans configurations, forming a flat α-system (IUPAC, 1989; Piironen et al., 2000). Moreover, sterols create planar surfaces, at both the top and the

Figure 2.9. Molecular structure of cholesterol and some abundant phytosterols (R = H– cholesterol; R = CH2CH3-β-sitosterol; R = CH2CH3 and additional double bond at C22-stigamsterol; R = CH3-campasterol; R = CH3 and additional double bond at C22-brassicasterol. (Adapted from Garti, 2004, with permission from the publisher.)



25

bottom of the molecules, since the R-conformation is preferred in the side chain linked to C20 carbon atom of the sterol molecule. This allows for multiple hydrophobic interactions between the rigid sterol nucleus (the polycyclic component) and the membrane matrix (Nes, 1987; Bloch, 1988; Piironen et al., 2000). Only side chains of the various sterols are different. These minor configuration differences result in major differences in their biological function. Peterson et al. (1951) reported that addition of soy sterols to a cholesterol-enriched diet prevented an increase in the plasma cholesterol level. This effect significantly reduced the incidence of atherosclerotic plaque (Peterson et al., 1951). Since then, numerous clinical investigations have indicated that administration of phytosterols to human subjects reduces the total plasma cholesterol and LDL cholesterol levels (Pelletier et al., 1995; Jones et al., 1997). Because of their poor solubility and limited bioavailability, high doses were required to have a noticeable effect. Up to 25 g/day of phytosterol esters were recommended in some reports and up to 1.3 g/day of phytosterol esters are to be used as per the FDA recommendation for a decrease of up to 15% of the cholesterol in the blood stream. The exact mechanism by which phytosterols inhibit the uptake of dietary and endogenous cholesterol is not completely understood. One theory suggests that cholesterol in the presence of phytosterols precipitates in a nonabsorbable state. A second theory suggests that cholesterol is displaced by phytosterols in the bile salt micelles and phospholipidcontaining mixed micelles, thus preventing its absorption (Hicks and Moreau, 2001). Enhanced solubilization of phytosterols in o/w microemulsions has been hypothesized to promote their bioavailability and maximize their absorption in human tissues owing to their small droplet size (in the range of several nanometers). Activity of phytosterols in food formulations has not yet been fully studied. Our results (Rozner and Garti, 2006) and that of other investigators (Ostlund, 2002) indicate that phytosterols do not cross human membranes, but they significantly retard (or prevent) the penetration of cholesterol and other lipids. We explored the ability of the unique dilutable microemulsions to solubilize phytosterols and studied the correlation between the solubilization capacity of the phytosterols and the microemulsion microstructure transitions (Spernath, 2003; Garti et al., 2005). Typical solubilization capacity of phytosterols and cholesterol along dilution line T64 are shown in Figure 2.10. The solubilization capacity of phytosterols in concentrated reverse micelle solution–like systems containing surfactant and oil phase (at 6:4 weight ratio, respectively), is 60,000 ppm (6 wt%). As can be seen from Figure 2.10, the solubilization

Figure 2.10. Solubilization capacity (SC) of cholesterol (x) and phytosterols (ο) along dilution line T64 at 25ºC.

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Chapter 2

capacity of phytosterols decreases with the increase in aqueous phase concentration. In a microemulsion containing 90 wt% aqueous phase, the maximum solubilization capacity is only 2400 ppm, that is, a decrease of 96% in the solubilization capacity of phytosterols. A possible explanation for the dramatic decrease in the solubilization capacity could be related to the nature of the solubilized molecules and to the locus of its solubilization at the interface. In concentrates (without added water), phytosterols are entrapped at the micelle’s interface. As more aqueous phase is added, water-in-oil swollen reverse micelles (w/o microemulsions) are formed, and the hydrophilic OH groups of the phytosterols are oriented toward the aqueous phase, causing the molecules to pack between the surfactant hydrophobic chains. This change in the locus of solubilization causes a decrease in solubilization capacity of the interface. Suratkar and Mahapatra (2000) observed a similar change in the locus of solubilization of phenolic compounds in sodium dodecyl sulfate (SDS) micelles. The decrease in solubilization capacity as the aqueous phase concentration increases may be attributed to microstructure transformations. The structural transformation from w/o to o/w microstructure via bicontinuous mesophase forces the phytosterols to solubilize between the hydrophobic amphiphilic chains. This less-preferable location causes a decrease in the solubilization capacity. It seems that the phytosterols have a strong effect on the spontaneous curvature of the micelles. As a result, the interface curvature decreases at lower water concentration. This effect is more pronounced in the presence of phytosterols than in empty micelles or in the presence of lycopene. The effect of phytosterol on cholesterol trans-membrane penetration was extensively studied. Various mechanisms have been suggested for the decrease in the transport of cholesterol in the presence of phytosterols (Trautwein et al., 2003; Hui and Howles, 2005; Rozner and Garti, 2006). Similarly, the competitive adsorption of cholesterol and phytosterols in the microemulsion membrane indicates that reverse microemulsions (w/o) preferentially solubilize more cholesterol over phytosterols. Nevertheless, upon dilution, once inversion to o/w microemulsions occurs, the phytosterols are somewhat better accommodated at the interface and they displace some of the cholesterol molecules from the interface (Figure 2.11).

Lutein and Lutein Ester Evidence that the macular pigment carotenoids—lutein and zeaxanthin—play an important role in the prevention of age-related-macular degeneration, cataract and other blinding disorders, is now available (Vandamme, 2002; Bone et al., 2003; Semba and Dagnelic, 2003; Kim et al., 2006). Carotenoids are situated in the macula (macula lutea, yellow spot) between the incoming photons and the photoreceptors and have maximum absorption at 445 nm for lutein and 451 nm for zeaxanthin. As a result, lutein and zeaxanthin can function as a blue light filter (400–460 nm). The blue light enters the inner retinal layers, thereby causing the carotenoids to attenuate their intensity. In addition to the protective effect of the macula from blue wavelength damage, these carotenoids can also improve visual acuity and scavenge harmful reactive oxygen species that are formed in the photoreceptors (Bone et al., 2003; Kim et al., 2006). With aging, some of the eye antioxidant supplies are diminished and antioxidant enzymes are inactivated. This action appears to be related to the accumulation, aggregation, and eventual precipitation in lens opacities of damaged proteins, subsequently leading to numerous eye disorders (Vandamme, 2002; Semba and Dagnelie, 2003).



27

Figure 2.11. Competitive solubilization of (a, b) cholesterol alone and (c, d) combined phytosterols and cholesterol in bile salt micelles (wt ratio of 1/1) in U-type microemulsions as a function of water dilution. (Adapted from Garti, with permission from the publisher.)

To improve the understanding of the potential benefits of carotenoids in general and lutein in particular, it is important to obtain more insight into their bioavailability and the factors that determine their absorption and bioavailability. Lutein, a naturally occurring carotenoid (Figure 2.12), is widely distributed in fruits and vegetables and is particularly concentrated in the Tagetes erecta flower. Epidemiological studies suggest that high lutein intake (6 mg/day) increases serum levels that are associated with a lower risk of cataract and age-related-macular degeneration. Lutein can be extracted either as a free form or as esterified (myristate, palmitate, or stearate) lutein. Both forms are practically insoluble in aqueous systems, resulting in low bioavailability. To improve its bioavailability, lutein was solubilized in U-type microemulsions based on R(+)-limonene. Some of the main findings are (Amar-Yuli et al., 2003, 2004; Garti et al., 2003; Amar-Yuli and Garti, 2006): (1) reverse micellar and w/o compositions solubilized both lutein and lutein ester better than o/w microemulsions, while maximum solubilization is obtained within the bicontinuous phase; (2) free lutein is solubilized better than the esterified one in the w/o microemulsions, whereas the esterified lutein is better accommodated within the o/w microemulsion; (3) vegetable oils decrease the solubilization of free lutein; (4) glycerol and alcohol enhance the solubilization of both luteins; and (5) solubilization is surfactant-dependent in all mesophase structures, but its strongest effect is in the bicontinuous phase.

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Chapter 2

(a) OH

HO (b)

Figure 2.12.

Chemical structures of (a) free lutein and (b) lutein ester.

On the basis of self-diffusion coefficients of each of the ingredients, a schematic model of the solubilization of lutein in the three possible structures along the dilution line 73 (70 wt% surfactant phase and 30 wt% oil phase) was constructed. The schematic location of the lutein at the structures is shown in Figure 2.13.

Vitamin E Microemulsions can also serve as reservoirs for enhanced solubility of lipophilic vitamins or other nutraceuticals within water-based formulations. The pharmaceutical literature is replete with studies of enhanced micellar delivery of vitamins, in particular vitamin E, vitamin K1, and β-carotene (Winn et al., 1989; Traber, 2004). Vitamin E (Figure 2.14), the major lipophilic antioxidant in human body, has invoked a great deal of interest regarding its disease-preventive and health-promoting effects, as well as its unique chemical structure, as a group of amphiphilic homologues exhibiting important interfacial roles in surfactant self-assemblies. Much interest has been devoted to microemulsions as efficient cosmetic and drug delivery systems, enabling the solubilization of hydrophobic active matter in aqueous media and improving its bioavailability. Therefore, we found it imperative to study the effect of microemulsion composition on the solubilization capacity of different forms of vitamin E and to infer the structural transformations from the solubilization data. Our results (Garti et al., 2004a, b) (Figure 2.15) show the following: (1) The solubilization capacity of α-tocopherols with free-OH head groups in Tween 60-based microemulsions drops abruptly at either of the two dilution lines that have been studied at constant surfactant-to-oil ratio, signifying structural transformations in the microemulsion structure. (2) The number of methyl groups on the vitamin’s polar head has an influence on the point at which the solubilization drop occurs, while nonsaturation of the hydrophobic tail of the vitamin enhances its solubilization capacity with no observable impact on the solubilization pattern. (3) In contrast to the free-OH vitamin E forms, the acetate form showed continuous decreases in solubilization capacity along the dilution line. (4) The type of oil used in the microemulsion has a strong influence on the solubilization pattern of the vitamin.


Figure 2.13.

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Schematic model of lutein solubilization.

(a)

CH3 HO 2R

H3C

O CH3

CH3 (b)

CH3

CH3

4⬘R

8⬘R

CH3 CH3

CH3 O

H3C

2R

CH3

CH3

4⬘R

8⬘R

CH3

O O

CH3 CH3 Figure 2.14.

CH3

CH3

Chemical structures of (a) α-tocopherol and (b) α-tocopherol acetate.

29


30

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Chapter 2

Figure 2.15. Solubilization capacities of free tocopherol (•) and tocopherol acetate (▲) in U-type microemulsions at several dilutions along dilution line 64 (60% surfactant phase and 40 wt% oil phase. (Adapted from Garti, 2002, with permission from the publisher.)

Triacetin attained a higher solubilization capacity of vitamin E than R(+)-limonene with a certain retardation in the structural transformations along the dilution line. Medium-chain triglycerides (MCT), on the other hand, maintained a constant ratio of TocOH to surfactant with an increasing level of aqueous phase within a certain range, while the solubilization capacity of D-α-tocopherol acetate (TocAc) decreased significantly in the same dilution range. (5) Alcohol cosurfactants and propylene glycol (PG) were found to be vitally important for improving the solubilization capacity of TocAc and TocOH. The latter showed a higher boost of solubilization at high levels of alcohols. (6) TocAc was found to prefer higher concentrations of Tween 60 for better solubilization, while TocOH prefers moderate levels. Mixing Tween 60 with diglycerol monooleate (DGM) displayed a pronounced enhancement in the solubilization of TocAc, while it caused a significant decrease in that of TocOH. Based on these findings, a commercial vitamin E clear beverage was developed. We have demonstrated that molecules such as essential oils, aromas, isoflavones, β-carotene, and lipoic acid have been similarly solubilized in the NSSL vehicles.

Oxidative Stability In many cases, NSSL vehicles are loaded with nutraceuticals that are very sensitive to oxidation. Any preparation containing these formulations should be stable for very long periods of time on the shelf and within the final product. Therefore, protection against environmental oxidative attack is essential. Micelles are very dynamic systems with a very fast exchange of the surfactant molecules between the interface and the continuous phase. Microemulsions are swollen micelles with similar fast exchange. However, systems that are rich in surfactant content form very concentrated phases, where the swollen micelles (the droplets) are tightly packed. Very condensed packed systems with strong inter-droplet interactions are obtained. In these systems the mobility of the surfactants is very restricted. In addition, stability was found to be dependent on the nature of the surfactant; therefore, even more tightly packed, worm–like, and entangled giant micelles can be formed. The stability against oxidation of lycopene, known for its poor oxidative stability once dissolved in solvents, was evaluated. Lycopene, if exposed to air and light, will be much


% of lycopene from original


31

100 Emulsion NSSL

75 50 25 0 0

28

52

72

Time (days) Figure 2.16. Oxidative stability to air and light of 23 mg lycopene emulsified in 10 g of o/w emulsion versus in the NSSL (modified microemulsion) vehicles.

more stable against autooxidation when solubilized in NSSL vehicles than if loaded onto emulsion droplets, as shown in Figure 2.16. After a few weeks, the emulsified lycopene was totally oxidized, while over 65 wt% of the NSSL lycopene remained stable. Similar results were obtained with other nutraceuticals (private communications).

Bioavailability Some nutraceuticals are known to be practically insoluble in water and, therefore, tablets or capsules that are taken orally tend to precipitate once the active ingredient is diluted with water (in human digestive tracts). As a result, the bioavailability is very limited, and the adsorption from the intestine to the blood serum is poorly controlled. Moreover, tablets and capsules exhibit strong fluctuations and as a result their activity is questionable. Two such examples that are discussed are CoQ10 and lycopene.

CoQ10 and Improved Bioavailability Coenzyme Q10 and related ubiquinones were first discovered in 1955 and were extracted and isolated from the mitochondria. The number of side chain isoprenoid units determines the nomenclature. Coenzyme Q6 is found in bacteria, whereas CoQ10 is found in mammalian mitochondria. CoQ10 is one part of a complex series of reactions that occur within mitochondria—ultimately linked to the generation of energy within a cell. The chemical structure of a CoQ10 is depicted in Figure 2.17.

Figure 2.17.

Chemical structure of CoQ10.

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Chapter 2

Virtually every cell in the human body contains coenzyme Q10. The mitochondria, the area of cells where energy is produced, contains most of the human coenzyme Q10. The heart and the liver, due to their high content of mitochondria per cell, contain the greatest quantity of coenzyme Q10. Coenzyme Q10 supplementation has helped some people with congestive heart failure (Salles et al., 2006; Yamamoto, 2006). Ubiquinone, or coenzyme Q10, is an important heart nutrient, used primarily by those who take pills against high cholesterol levels. Certain lipid-lowering drugs, such as statins as well as oral agents, which lower blood sugar, cause a decrease in serum levels of coenzyme Q10 and reduce the effects of coenzyme Q10 supplementation (Mortensen et al., 1997; Palomaki et al., 1998; Lankin, 2003; Passi et al., 2003; Bettowski, 2005; Cenedella et al., 2005; Hargreaves et al., 2005; Mabuchi et al., 2005; Strey et al., 2005). These drugs inhibit the production of coenzyme Q10 by the liver, and will cause serious complications, unless one supplements coenzyme Q10 back into the diet. A prescription for lipid-lowering statin drugs should always be accompanied with a recommendation to take coenzyme Q10, because if a person is deficient in coenzyme Q10, heart failure is more likely. The second major use of coenzyme Q10 would be in the case of congestive heart failure, where it is particularly effective. Its importance to the human heart is illustrated by the fact that the heart may cease to function when coenzyme Q10 levels fall by 75%. Schematic activity within the mitochondria of CoQ10 is demonstrated in Figure 2.18. Adenosine triphosphate (ATP) is present in every cell of human organs. It serves as a source of energy for many of the body’s biochemical processes and represents the reserve

Figure 2.18.

Schematic functionality of CoQ10 in mitochondria.



33

Figure 2.19. Bioavailability of CoQ10 in humans given a total of 150 mg of active matter in two daily doses in two types of formulations, in best commercial formulation in the market place (entitled 275% more bioavailable, filled bar) versus the CoQ10 solubilized in NSSL vehicles (white bar).

energy in the muscles. The heart needs a constant supply of ATP, which cannot be produced without coenzyme Q10. Coenzyme Q10 is the catalyst for the creation of ATP. This means that coenzyme Q10 plays a vital role in the inner workings of the human body. Several other chronic diseases are associated with lack of CoQ10 such as Parkinson’s disease (Andrey and Gille, 2003; Batandier et al., 2004; Genova et al., 2004; Sharma et al., 2004; Arroyo and Navas, 2005; Ebadi et al., 2005; Dhanasekaran and Ren, 2005; Moriera et al., 2005). It is also a potent antioxidant since it fights the harmful free radicals generated during normal metabolism. The highest dietary sources of CoQ10 come from fresh sardines and mackerel, the heart, the liver, and beef, lamb, and pork, as well as from eggs. There are plenty of vegetable sources of CoQ10, the richest being spinach, broccoli, peanuts, wheat germ, and whole grains, although the amount is significantly smaller than that found in meat. Coenzyme Q10 is primarily offered in tablet, capsule, or soft gel forms containing a yellow-orange powder. The tablet form, being much less digestible, is not recommended. Adult levels of supplementation are usually 30–90 mg/day, although individuals with specific health conditions may supplement with higher levels, such as 100 mg 3–4 times per day. Most of the research on heart conditions has used 90–150 mg/day. CoQ10 is fat soluble and, like most other fat-soluble compounds, is poorly absorbed from the gastrointestinal tract, especially when taken on an empty stomach. Therefore, it is recommended that CoQ10 be taken with a meal or in a formulation, such as oil phase, that will improve its bioavailability and, hence, absorption. Our studies on humans were conducted at the Technical University of Tokyo by Prof. Yamamoto on eight individuals who were fed for 28 days with CoQ10 from a commercial product known as “275% more bioavailable”: and with our NSSL vehicles incorporated into soft gels. The individual intake was of 150 mg CoQ10 per day (Yamamoto, 2005). The efficacy of the NSSL-based formulations versus the commercial product is demonstrated in Figures 2.19–2.21. It can be clearly concluded that (1) CoQ10 in the NSSL vehicles is more bioavailable than the commercial product in soft gels (claimed to be 275% more bioavailable than other products in tablets); (2) the ratio of total CoQ10 to total cholesterol in the blood stream derived from the NSSL soft gels is higher than from the commercial product, indicating that the NSSL vehicles provide extra activity to the CoQ10, which assists in maintaining total cholesterol at lower levels; (3) it is well documented that several nutraceuticals and oil-soluble phytochemicals tend to interfere with the absorption of

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Chapter 2

Figure 2.20. Ratio of CoQ10 (TQ) to total cholesterol (TC) in human blood when given 150 mg of CoQ10 in two daily doses in two types of formulations, in best commercial formulation in the market place (entitled 275% more bioavailable, filled bar) versus the CoQ10 solubilized in NSSL vehicles (white bar).

Figure 2.21. Ratio of vitamin E (VE) to total cholesterol in human blood given a total of 150 mg of CoQ10 in two daily doses in two types of formulations, in best commercial formulation in the market place (entitled 275% more bioavailable, filled bar) versus the CoQ10 solubilized in NSSL vehicles (white bar).

vitamins. Therefore, it was expected that the vitamin E levels in the blood stream would decrease with the intake of CoQ10. However, it was found in the human blood tests that vitamin E levels did not decrease in the presence of CoQ10 when CoQ10 was taken in the NSSL vehicles. In fact, it remained at higher levels when compared to its levels derived from the commercial product. On the basis of these and other findings, we have proposed a highly schematic cartooned model (Figure 2.22) of the transport of the nutraceuticals across human membranes. The model shows how the vehicle that is dispersed in the aqueous phase approaches the membrane and adheres to it. The CoQ10 is transported across the membrane, while the empty vehicles depart and are excreted from the digestive tract. It should be noted that the surfactants do not cross the membrane.

Water Binding The activity of water plays a significant role in any reaction (chemical or enzymatic) that exists in food systems and related products. Microemulsions of w/o can serve as microreactors for several such processes, mainly for Maillard reactions (Lutz et al., 2005). Water-in-oil nanodroplets can be free or bound to the head groups of the surfactants. Thus, the ability to



35

Figure 2.22. Schematic representation of the microemulsion droplet approaching the membrane and releasing the nutraceutical molecules. The surfactant does not cross the membrane.

estimate the activity of the water and the binding capacity of the surfactants is of high importance whenever a triggered reaction is required. At certain water levels, the water in the core of the microemulsion will be bound and the activity will be minimal; thus, the reactivity of the ingredients (sugars and proteins in Maillard reactions or enzymes in hydrolysis processes) will be low. Upon adding more water and reaching a point where the water becomes free, the reactions will be triggered (Yaghmur et al., 2003a, b). We (Spernath, 2003; Yamomoto, 2006) examined, by a sub-zero differential scanning calorimeter (DSC) technique, the nature of the water in the confined space of a w/o microemulsion, to better understand the role of the entrapped water, in order to control enzymatic reactions carried out in the inner phase (Spernath et al., 2003; Yaghmur et al., 2003). We reported (Figure 2.23) that the surfactant/alcohol/PG can strongly bind water in the inner phase, so that it freezes below –10°C and acts, in part, as bound water and, in part, as non-freezable water (Spernath et al., 2003). Even after complete inversion to o/w microemulsions, the water in the continuous phase strongly interacts with the cosolvent/surfactant and remains partially bound. The water in the core of nonionic microemulsions containing, in addition to the surfactants, polyols and alcohol, is strongly bound to the surfactant head group and/or to the polyol groups and freezes at subzero temperatures. The amount of bound water strongly depends on the amounts of the surfactants present in each microdroplet, on the nature of the head groups, and on the amounts of cosolvents (alcohol and PG). On the basis of these findings, Maillard reactions, model reactions of furfural and cysteine and glucose and isoleucine (Ezrahi et al., 2001; Fanun et al., 2001; Yaghmur et al., 2002a, b, 2003, 2005; Lutz et al., 2005), as well as hydrolysis of phosphatidylcholine by phospholipase L2 (PLA2) to lysolecithin (Garti et al., 1997) were studied. It was found that the reactions do not start (lag time) until sufficient water is added to exceed the free water threshold. The reactions are, therefore, very well triggered and controlled by the water activity within the core of the microdroplets. The reaction rates can be delayed or speeded by immobilizing (confining) or freeing the water in the core of the microdroplets.

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Water content (wt%) Figure 2.23. The amounts (weight percent of free and bound) of interphasal water in microemulsions based on sugar esters along dilution line 64 (60% surfactant and 40% oil phase). (o) Bulk (free) water and (•) interphasal (bound) water. (Adapted from Garti, 1995, with permission from the publisher.)

Conclusions Microemulsions have been known for several decades, but their utilization in food systems has been very limited owing to some major structural limitations and the nature of the surfactants and the oils. Another major drawback is that in most cases they were undilutable with water. In recent years, after significant efforts by colloid chemists, experimentalists, and others, some of the key characteristics related to the packing of the surfactant, free energy gain, geometries, and so on, shed light on the basic requirements needed to design U-type phase diagrams. The latter consist of large isotropic regions and have proved capable of making concentrates that can be easily diluted with water and oil phases. In the course of our studies we also learned that: • Self-assembled, hydrophilic surfactant in oil phase, in the presence of cosolvents and cosurfactants, can provide high solubilization capacities for entrapment of immiscible phases and active guest molecules. These microstructures can be diluted with excess water to form crystal-clear (transparent) solution-like, isotropic phases, loaded with the active matter. • If the ingredients composing the microemulsions and the cosolvents and cosurfactants are carefully selected, one can form a variety of beverage microemulsions. • Microemulsions of U-type with progressive full dilution with aqueous phase can be formulated.



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• Microemulsions of w/o and bicontinuous structures, as well as o/w microemulsions can solubilize guest molecules at their interface at high solubilization capacities, in some cases up to 100-fold of the solubility of the nutraceuticals in the corresponding solvent! • Molecules such as lycopene, vitamin E, tocopherols and tocopherol acetate, β-carotene, lutein, phytosterols, and CoQ10 can be quantitatively solubilized. • Microemulsions provide some oxidative protection to the nutraceuticals. • Various other guest molecules such as aromas, flavors, and antioxidants can be solubilized in the microemulsions. • Water entrapped at the core of a w/o microemulsion can be strongly bound to the surfactant head group that will restrict the water activity. Thus, upon adding more water, the reaction by the enzyme or regents can be triggered. It seems that we are now ready to start using microemulsions in beverages and other food systems and to incorporate active ingredients within high-quality food for the benefit of human nutrition and health.

References Alander, J.; Warnheim, T. 1989a. Model microemulsions containing vegetable-oils. 1. nonionic surfactant systems. JAOCS 66:1656–1660. Alander, J.; Warnheim, T. 1989b. Model microemulsions containing vegetable-oils. 2. ionic surfactant systems. JAOCS 66:1661–1665. Amar-Yuli, I.; Garti, N. 2006. Progress in Structural Transformation in Lyotropic Liquid Crystals. Colloids and Surfaces 282: 435–456. Amar-Yuli, I.; Aserin, A.; Garti, N. 2003. Solubilization patterns of lutein and lutein esters in food grade nonionic microemulsions. J. Agric. Food Chem. 51(16):4775–4781. Amar-Yuli, I.; Aserin, A.; Garti, N. 2004. Microstructure transitions derived from solubilization of lutein and lutein esters in food microemulsions. Colloids Surfaces B, 33:143–150. Andrey, V.; Gille, L. 2003. The biomolecule ubiquinone exerts a variety of biological functions. BioFactors 18(1–4):23–31. Arroyo, A.; Navas, P. 2005. Specificity of coenzyme Q10 for a balanced function of respiratory chain and endogenous ubiquinone biosynthesis in human cells. Biochim. Biophys. Acta, Bioenergetics 1706(1–2):174–183. Batandier, C.; Leverve, X.; Fontaine, E. 2004. Opening of the mitochondrial permeability transition pore induces reactive oxygen species production at the level of the respiratory chain complex I. J. Biol. Chem. 279(17):17197–17204. Bettowski, J. 2005. Statins and modulation of oxidative stress. Toxicol. Mech. Meth. 15(2):61–92. Billman, J.F.; Kaler, E.W. 1991. Structure and phase-behavior in 4 component nonionic microemulsions. Langmuir 7:1609–1617. Bloch, K. 1988. Sterol structure and function. J. Am. Oil Chem. Soc. 65:1763–1766. Bone, R.A.; Landrum, J.T.; Guerra, L.H.; Ruiz, C.A. 2003. Lutein and zeaxanthin dietary supplements raise macular pigment density and serum concentrations of these carotenoids in humans. J. Nutrition 133(4):992–998. Bramley, P.M. 2000. Is lycopene beneficial to human health? Phytochemistry 54:233–236. Cenedella, R.J.; Neely, A.R.; Sexton, P. 2005. Concentration and distribution of ubiquinone (coenzyme Q), the endogenous lipid antioxidant, in the rat lens: effect of treatment with simvastatin. Mol. Vis. 11:594–602. Constantinides, P.P.; Scalart, J.P. 1997. Formation and physical characterization of water-in-oil microemulsions containing long- versus medium-chain glycerides. Int. J. Pharm. 158:57–68. Cooke, J.P. 1998. Nutraceuticals for cardiovascular health. Am. J. Cardiol. 82:43S–46S. de Campo, L.; Yaghmur, A.; Garti, N.; Leser, M.E.; Glatter, O. 2004. Food-grade microemulsions: structural characterization. J. Colloid Interface Sci. 274(1):251–267. Dhanasekaran, M.; Ren, J. 2005. The emerging role of coenzyme Q-10 in aging, neurodegeneration, cardiovascular disease, cancer and diabetes mellitus. Curr. Neurovasc. Res. 2(5):447–459. Dungan, S.R. 1997. “Microemulsions in Foods: Properties and Applications.” In: Industrial Applications of Microemulsions, edited by C. Solans and H. Kunieda, pp. 148–170. Marcel Dekker Inc.

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Ebadi, M.; Brown-Borg, H.; El Refaely, H.; Singh, B.B.; Garret, S.; Shavali, S.; Sharma, S.K. 2005. Metallothioneinmediated neuro protection in genetically engineered mouse models of Parkinson’s disease. Molecular Brain Res. 134(1):67–75. Ezrahi, S.; Aserin, A.; Garti, N. 1999. “Aggregation Behavior in One-Phase (Winsor IV) Microemulsion Systems.” In Handbook of Microemulsion Science and Technology, edited by P. Kumar and K.L. Mittal, pp. 185–246. Marcel Dekker Inc. Ezrahi, S.; Aserin, A.; Fanun, M.; Garti, N. 2001. “Subzero Temprature Behavior of Water in Microemulsions.” In Thermal Behavior of Dispersed Systems, edited by N. Garti, pp. 59–120. Marcel Dekker Inc. Fanun, M.; Leser, M.; Aserin, A.; Garti, N. 2001. Sucrose ester microemulsions as microemulsions as microreactors for model Maillard reaction. Colloids Surfaces A: Physicochem. Eng. Asp. 194(1–3):175–187. Garti, N.; Aserin, A.; Mytayeva, U. 2007. Submitted for publication. Garti, N.; Lichtenberg, D.; Silberstein, T. 1997. The hydrolysis of phosphatidylcholine A2 in microemulsion as microreactor. Colloids Surfaces A: Physicochem. Eng. Asp. 128(1–3):17–25. Garti, N.; Clement, V.; Fanun, M.; Leser, M.E. 2000a. Some characteristics of sugar ester nonionic microemulsions in view of possible food applications. J. Agric. Food Chem. 48(9):3945–3956. Garti, N.; Aserin, A.; Fanun, M. 2000b. Non-ionic sucrose esters microemulsions for food applications. Part 1. Water solubilization. Colloids Surfaces A: Physicochem. Eng. Asp. 164(1):27–38. Garti, N; Yaghmur, A; Leser, M.E; Clement,V; Watzke, H.J. 2001. Improved oil solubilization in O/W food-grade microemulsions in the presence of polyols and ethanol. J. Agric. Food Chem. 49:2552–2562. Garti, N.; Amar, I.; Yaghmur, A.; Spernath, A. 2003. Interfacial modification and structural transitions induced by guest molecules solubilized in U-type nonionic food-grade microemulsions. J. Disper. Sci. Technol. 24(3 and 4):397–410. Garti, N.; Yaghmur, A.; Aserin, A.; Spernath, A.; Elfakess, R.; Ezrahi, S. 2004a. Solubilization of active molecules in microemulsions for improved solubilization, and environmental protection. Colloids Surfaces A: Physicochem. Eng. Asp. 230(1–3):183–190. Garti, N.; Zakharia, I.; Spernath, A.; Yaghmur, A.; Aserin, A.; Hoffman, R.E.; Jacobs, L. 2004b. Solubilization of water-insoluble nutraceuticals in nonionic microemulsions for water-based use. Progr. Colloid Polym. Sci. 126:184–189. Garti, N.; Spernath, A.; Aserin, A.; Lutz, R. 2005. Nano-sized self-assemblies of nonionic surfactants as solubilization reservoirs and microreactors for food systems. Soft Matter 1:206–218. Garti, N.; Aserin, A.; Mytayeva, U. 2007. In preparation. Gasco, M.R. 1997. “Microemulsions in the Pharmaceutical Field: Perspectives and Applications.” In Industrial Applications of Microemulsions, edited by C. Solans and H. Kunieda, pp. 97–122. Marcel Dekker Inc. Genova, M.L.; Pich, M.M.; Bernacchia, A.; Binachi, C.; Biondi, A.; Bovina, C.; Falasca, A.I.; Formiggini, G.; Castelli, G.P.; Lenaz, G. 2004. The mitochondrial production of reactive oxygen species in relation to aging and pathology. Annals New York Academ. Sci. 1011:86–100. Hamdan, S.; Lizana, R.; Laili, C.R. 1995. Aqueous and nonaqueous microemulsion systems with a palm oil-base emollient. JAOCS 72:151–155. Hargreaves, L.P.; Duncan, A.J.; Heales, S.J.R.; Land, J.M. 2005. The effect of HMG-CoA reductase inhibitors on coenzyme Q10. Possible biochemical/clinical implications. Drug Safety 28(8):659–676. Hicks, K.B.; Moreau, R.A. 2001. Phytosterols and phytostanols: functional food cholesterol busters. Food Technol. 55:63–67. Holmberg, K. 1998. “Quarter Century Progress and New Horizons in Microemulsions.” In Micelles, Microemulsions, and Monolayers, edited by O. Shah, pp. 161–192. Marcel Dekker Inc. Hou, M.J.; Shah, D.O. 1987. Effects of the molecular structure of the interface and continuous phase on solubilization of water in water/oil microemulsions. Langmuir 3:1086–1096. Hui, D.Y.; Howles, P.N. 2005. Molecular mechanisms of cholesterol absorption and transport in the intestine. Semin. Dev. Biol. 16(2):183–192. Huibers, P.D.T.; Shah, D.O. 1997. Evidence for synergism in nonionic surfactant mixtures: enhancement of solubilization in water-in-oil microemulsions. Langmuir 13:5762–5765. IUPAC, The Nomenclature of Steroids (Recommendations 1989), International Union of Pure and Applied Chemistry and International Union of Biochemistry and Molecular Biology. Available: http:// www.chem.qmw.ac.uk/ iupac/steroid/ [1989]. Jones, P.J.H.; MacDougall, D.E.; Ntanios, F.; Vanstone, C.A. 1997. Dietary phytosterols as cholesterol-lowering agents in humans. Can. J. Physiol. Pharmac. 75:217–227.



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Joubran, R.F.; Cornell, D.G.; Parris, N. 1993. Microemulsions of triglyceride and non-ionic surfactant-effect of temperature and aqueous phase composition. Colloids Surf. A 80:153–160. Kahlweit, M.; Busse, G.; Faulhaber, B.; Jen, J. 1996. Shape changes of globules in nonionic microemulsions. J. Phys. Chem. 100:14991–14994. Kanei, N.; Tamura, Y.; Kunieda, H. 1999. Effect of types of perfume compounds on the hydrophile-lipophile balance temperature. J. Colloid Interface Sci. 218:13–22. Kim, S.R.; Nakanishi, K.; Itagaki, Y.; Sparrow, J.R. 2006. Photooxidation of A2-PE, a photoreceptor outer segment fluorophore, and protection by lutein and zeaxanthin. Experimental Eye Research 82(5):828–839. Lankin, V.Z.; Tikhaze, A.K.; Kukharchuk, V.V.; Konovalova, G.G.; Pisarenko, O.I.; Kaminnyi, A.I.; Shumaev, K.B.; Belenkov, Y.N. 2003. Antioxidants decreases the intensification of low density lipoprotein in vivo peroxidation during therapy with statins. Molecular Cell. Biochem. 249(1 and 2):129–140. Lutz, R.; Aserin, A.; Garti, N. 2005. Maillard reaction between leucine and glucose in o/w microemulsion media in comparison to aqueous solution. J. Disper. Sci. Tech. 26(5):535–547. Mabuchi, H.; Higashikata, T.; Kawashiri, M.; Katsuda, S.; Mizuno, M.; Nohara, A.; Inazu, A.; Koizumi, J.; Kobayashi, J. 2005. Reduction of serum ubiquinol-10 and ubiquinone-10 levels by atorvastatin in hypercholesterolemic patients. J. Atherosclerosis Thrombosis 12(2):111–119. Malcolmson, C.; Lawrence, M.J. 1995. Three-component non-ionic oil-in-water microemulsions using polyoxyethylene ether surfactants. Colloids Surfaces B: Biointerfaces 4:97–109. Moriera, P.I.; Santos, M.S.; Sena, C.; Nunes, E.; Seica, R.; Oliveira, C.R. 2005. CoQ10 therapy attenuates amyloid—peptides toxicity in brain mitochondria isolated from aged diabetic rats. Exp. Neurol. 196(1):112–119. Mortensen, S.A.; Leth, A.; Agner, E.; Rohde, M. 1997. Dose-related decreases of serum coenzyme Q10 during treatment with HMG-CoA reductase inhibitors. Molecular Aspects Med. 18(Suppl.):s137–s144. Nes, W.R. 1987. “Multiple Roles for Plant Sterols.” In The Metabolism, Structure and Function of Plant Lipids, edited by P.K. Stumpf, B.J. Mudd and W.R. Nes, pp. 3–9. Plenum Press. Palomaki, A.; Malminiemi, K.; Solakivi, T.; Malminiemi, O. 1998. Ubiquinone supplementation during lovastatin treatment: effect on LDL oxidation ex vivo. J. Lipid Res. 39(7):1430–1437. Park, K.M.; Kim, C.K. 1999. Preparation and evaluation of flurbiprofen-loaded microemulsion for parenteral delivery. Int. J. Pharm. 181:173–179. Passi, S.; Stancato, A.; Aleo, E.; Dmitrieva, A.; Littarru, G.P. 2003. Statins lower plasma and lymphocyte ubiquinol/ubiquinone withput affecting and PUFA. Biofactors 18(1–4):113–124. Pelletier, X.; Belbraouet, S.; Mirabel, D.; Mordret, F.; Perrin, J.L.; Pages, X.; Debry, G. 1995. A diet moderately enriched in phytosterols lowers plasma cholesterol concentrations in normocholesterolemic humans. Ann. Nutr. Metab. 39:291–295. Peterson, D.W.; Nichols, C.W.; Schneour E.W. 1951. Some relationships among dietary sterols, plasma and liver cholesterol levels and atherosclerosis in chicks. Proc. Soc. Exp. Biol. Med. 78:1143–1147. Piironen, V.; Lindsay, D.G.; Miettinen, T.A.; Toivo, J.; Lampi, A.M. 2000. Review—plant sterols: biosynthesis, biological function and their importance to human nutrition. J. Sci. Food Agric. 80:939–966. Prichanont, S.; Leak, D.J.; Stuckey D.C. 2000. The solubilization of mycobacterium in a water-in-oil microemulsion for biotransformations: system selection and characterization. Colloids Surfaces A: Physicochem. Eng. Asp. 166:177–186. Radomska, A.; Dobrucki, R. 2000. The use of some ingredients for microemulsion preparation containing retinol and its esters. Int. J. Pharm. 196:131–134. Rao, A.V.; Agarwal, S. 1999. Role of lycopene as antioxidant carotenoid in the prevention of chronic diseases: a review. Nutr. Res. 19:305–323. Regev, O.; Ezrahi, S.; Aserin, A.; Garti, N.; Wachtel, E.; Kaler, E.W.; Khan, A.; Talmon, Y. 1996. A study of the microstructure of a four-component nonionic microemulsion by cryo-TEM, NMR, SAXS, and SANS. Langmuir 12:668–674. Rozner, S.; Garti, N. 2006. The activity and absorption relationship of cholesterol and phytosterols. Colloids and Surfaces A: Physicochem. Eng. Aspects 282:435–456. Ostlund, R.E. Jr. 2002. Phytosterols in human nutrition. Annu. Rev. Nutr. 22:533–549. Salles, J.E.; Moises, V.A.; Almeida, D.R.; Chacra, A.R.; Moises, R.S. 2006. Myocardinal dysfunction in mitochondrial diabetes treated with Coenzyme Q10. Diabet. Res. Clin. Pract. 72(1):100–103. Semba, R.D.; Dagnelie, G. 2003. Are lutein and zeaxanthin conditionally essential nutrients for eye health? Med. Hypotheses 61(4):465–472.

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Sharma, S.; Kheradpezhou, M.; Shavali, S.; El Refaely, H.; Eken, J.; Hagen, C.; Ebadi, M. 2004. Neuroprotective actions of coenzyme Q10 in Parkinson’s disease. Meth. Enzymol. 382(Quinones and Quinone Enzymes, Part B):488–509. Shinoda, K.; Lindman, B. 1987. Organized surfactant systems: microemulsions. Langmuir 3:135–149. Solans, C.; Pons, R.; Kunieda, H. 1997. “Overview of Basic Aspects of Microemulsions.” In Industrial Applications of Microemulsions, edited by C. Solans and H. Kunieda, pp. 1–17. Marcel Dekker Inc. Spernath, A.; Yaghmur, A.; Aserin, A.; Hoffman, R.E.; Garti, N. 2002. Food grade microemulsions based on nonionic emulsifiers: media to enhance lycopene solubilization. J. Agric. Food Chem. 50:6917–6922. Spernath, A.; Yaghmur, A.; Aserin, A.; Hoffman, R.E.; Garti, N. 2003. Phytosterols solubilization capacity and microstructure transitions in Winsor IV food-grade microemulsions studied by self-diffusion NMR. J. Agric. Food Chem. 51(8):2359–2364. Strey, C.H.; Young, J.M.; Molyneux, S.L.; George, P.M.; Florkowski, C.M.; Scott, R.S.; Frampton, C.M. 2005. Endothelium-ameliorating effects of statin therapy and coenzyme Q10 reductions in chronic heart failure. Atherosclerosis 179:201–206. Suratkar, V.; Mahapatra, S. 2000. Solubilization site of organic perfume molecules in sodium dodecyl sulfate micelles: new insights from proton NMR studies. J. Colloid Interface Sci. 225:32–38. Tokuoka, Y.; Uchiyama, H.; Abe, M.; Christian, S.D. 1995. Solubilization of some synthetic perfumes by anionicnonionic mixed surfactant systems 1. Langmuir 11:725–729. Traber, M.G. 2004. The ABCs of vitamin E and β-carotene absorption. Am. J. Clin. Nutr. 80(1):3–4. Trautwein, E.A.; Duchateau, G.S.M.J.E.; Lin, Y.G.; Mel’nikov, S.M.; Molhuizen, H.O.F.; Ntanios, F.Y. 2003. Proposed mechanisms of cholesterol-lowering action of plant sterols. Eur. J. Lipid Sci. Technol. 105 (3–4):171–185. Trevino, S.F.; Joubran, R.; Parris, N.; Berk, N.F. 1998. Structure of a triglyceride microemulsion: a small-angle neutron scattering study. J. Phys. Chem. B 102:953–960. Trotta, M.; Morel, S.; Gasco, M.R. 1997. Effect of oil phase composition on the skin permeation of felodipine from o/w microemulsions. Pharmazie 52:50–53. Vandamme, T.F. 2002. Microemulsions as ocular drug delivery systems: recent developments and future challenges. Progr. Retinal Eye Res. 21(1):15–34. Van het Hof, K.H.; West, C.E.; Weststrate, J.A.; Hautvast, J.G.A.J. 2000. Dietary factors that affect the bioavailability of carotenoids. J. Nutr. 130:503–506. von Corswant, C.; Söderman, O. 1998. Effect of adding isopropyl myristate to microemulsions based on soybean phosphatidylcholine and triglyceride. Langmuir 14:3506–3511. von Corswant, C.; Engström, S.; Söderman, O. 1997. Microemulsions based on soybean phophatidylcholine and triglyceride phase behavior and microstructure. Langmuir 13:5061–5070. Warisnoicharoen, W.; Lansley, A.B.; Lawrence, M.J. 2000. Nonionic oil-in-water microemulsions: the effect of oil type on phase behavior. Int. J. Pharm. 198:7–27. Winn, M.J.; White, P.M.; Scott, A.K.; Pratt, S.K.; Park, B.K. 1989. The bioavailability of a mixed micellar preparation of vitamin K1, and its procoagulant effect in anticoagulated rabbits. J. Pharm. and Pharmacol. 41(4):257–260. Yaghmur, A.; Aserin, A.; Garti N. 2002a. Furfural-cysteine model reaction in food-grade nonionic o/w microemulsions for selective flavor formation. J. Agric. Food Chem. 50:2878–2883. Yaghmur, A.; Aserin, A.; Garti N. 2002b. Phase behavior of microemulsions based on food-grade nonionic surfactants: effect of polyols and short-chain alcohols. Colloids Surfaces A 209:71–81. Yaghmur, A.; Aserin, A.; Tiunova, I.; Garti, N. 2002c. Structural behavior of nonionic surfactants in the presence of propylene glycol in nonionic microemulsions studied by DSC. J. Thermal Anal. Cal. 69:163–177. Yaghmur, A.; Aserin, A.; Antalek, B.; Garti, N. 2003a. Microstructure of five-component food grade oil-in-water microemulsions by PGSE-NMR, conductivity, and viscosity. Langmuir 19(4):1063–1068. Yaghmur, A.; Fanun, M.; Aserin, A.; Garti, N. 2003b. “Food Grade Microemulsions Based on Nonionic Emulsifiers as Microreactors for Selective Flavor Formation by Maillard Reaction.” In Self-Assembly, edited by B.H. Robinson, pp. 144–151, IOS Press. Yaghmur, A.; de Campo, L.; Glatter, O.; Leser, M.E.; Garti, N. 2004. Structural characterization of fivecomponent food grade oil-in-water nonionic microemulsions. PCCP 6(7):1524–1533. Yaghmur, A.; Aserin, A.; Abbas, A.; Garti, N. 2005. Reactivity of furfural-cysteine model reaction in food grade five-component nonionic microemulsions. Colloids and Surfaces A 253(1–3):223–234. Yamamoto, Y. 2005. Private communication report. Yamamoto, Y. 2006. Coenzyme Q10, free radicals, and heart disease. Oxidative Stress and Disease 21(Molecular Interventions in Lifestyle-Related Diseases):37–46.

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Emulsions as Delivery Systems in Foods Ingrid A.M. Appelqvist, Matt Golding, Rob Vreeker, and Nicolaas Jan Zuidam

Introduction Many industries use emulsion technology as a delivery vehicle for either aqueous- or oilbased actives (or both). Examples include paint, pharmaceutical and bitumen industries. In all cases, there are two considerations that must be taken into account when formulating an emulsion for controlled delivery. First, the emulsion system must be (storage) stable right up to the point of application. Secondly, upon its application the emulsion should behave in a consistent manner so that it achieves the desired delivery. In many (but by no means all) cases this equates to the “making and breaking” of emulsions for stability and subsequent delivery. Emulsion systems are, of course, an integral part of food manufacturing. Emulsion technology in the context of foods is not in itself novel—examples include milk, dairy cream, and mayonnaise. The latter can be traced back to the 17th century. However, the use of emulsions as delivery vehicles represents a rapidly developing area for the application of emulsions within the food industry. Similar to other industries, same essential formulation and processing considerations apply. First, the emulsion should be stable up to the point of application—in other words: shelf stable. This is true for all food emulsions, although there may be significant variation in the length of time that the product is required to be stable. Generally, this is limited by the microbiological stability of the particular product: pasteurized emulsions, such as milk or cream, may have a two-week shelf life. In contrast, sterilized emulsions such as crème liqueurs may be stable for over a year. However, in all cases it is important that during the lifetime of the product the emulsion does not show signs of instability or phase separation. Secondly, the emulsion should be designed so that it performs in a defined manner upon application. In food products, there are effectively two main points of application: consumption and digestion. From a consumer perspective, the first point of application might be construed as being the most important. The whole sensory experience of food is dominated by its behavior in the mouth. Emulsions play an important role here, both in terms of flavor delivery and release and in terms of textural behavior and response in the mouth. Mouth is a remarkably sensitive tool at differentiating between organoleptic sensations— most of us are able to differentiate between skimmed, semi-skimmed and whole milk. Consequently, even small changes to emulsion composition and in-mouth behavior can have a significant impact on whether a particular product is perceived in a positive or negative way.

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Chapter 3

In recent years, consumer demand for highly nutritional food products has increased and can be interpreted as: 1. removal of so-called “bad” ingredients, such as sugar, fat (saturated or trans) and salt; 2. enhancement of “good” ingredients, such as fiber, protein or fruit and vegetable content and; 3. direct fortification with actives, such as vitamins, minerals, ω-3 oils. In all cases it is important that not only there is no compromise in quality but also any claimed fortification should have good bioavailability during digestion. Consequently, in addition to in-mouth behavior, emulsion systems are becoming increasingly utilized in food products as a means of achieving controlled delivery in the gastrointestinal (GI) tract as well. This chapter highlights recent developments in the application of food emulsions as delivery vehicles from the consideration of both mouth and gut as areas for targeted delivery. We aim to demonstrate the technical challenges and solutions for delivering both oil- and water-soluble actives, providing examples from flavor delivery in mouth to delivery of active compounds and sterols under gastric conditions. We also aim to show how nature can provide solutions for the application of emulsions as delivery systems, as well as looking at future developments and opportunities in this richly diverse field.

Stabilization and Destabilization of Emulsion Systems Emulsion Stabilization Processed foods are often complex multiphase systems. In the cases where both water and oil are present, emulsification is of course necessary to prevent separation of these two incompatible phases. Emulsion design within the food industry is not a trivial issue. The diversity of manufactured food and beverages means that the relative balance of water and oil phases can vary widely depending on product type, and both oil-in-water (o/w) and water-in-oil (w/o) type emulsions have found a wide variety of applications. Some examples of food emulsions along with concentrations of water and oil are given in Table 3.1. Food emulsions are created and stabilized through a combination of process and formulation design. Homogenization facilitates droplet break-up to create the dispersed phase, whilst food ingredients displaying appropriate amphipathic properties are able to adsorb onto the newly formed droplet interfaces during homogenization to provide electrostatic Table 3.1.

Examples of typical food emulsions and their relative concentration of fat

Food Milk Ice creama Cream Light mayonnaise Mayonnaise Butter Margarine a

Emulsion type

Fat/oil content (wt%)

o/w o/w o/w o/w o/w w/o w/o

0–4 0–10 20–50 20–50 65–75 80 80

Ice cream can be considered as a four-phase colloid, comprising dispersed phases of ice, air, and fat in a concentrated continuous phase.


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Emulsions as Delivery Systems in Foods

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(formation of a charged interface) or steric (formation of a viscoelastic interface) stabilization against immediate coalescence. It can be noted that industrial manufacturing of food emulsions generally employs only a limited number of homogenization technologies, depending on product type. Colloid or Ross mills are commonly used in the manufacture of mayonnaise or similar products with high oil content. High-pressure homogenizers are used in the manufacture of such products as ice cream, (homogenized) milk, and other beverages as well as many other soft solid products of low-to-intermediate fat content. Water-in-oil emulsions, such as margarines, are most commonly prepared on votator lines. Other aspects of processing, too, play an important role in the formation of food emulsions, such as pre-homogenization and thermal treatment (pasteurization, sterilization); however, these will not be discussed as part of this chapter. More information on the processing aspects of food emulsions can be found in the literature (Paquin, 1999; Schultz et al., 2004; Perrier-Cornet et al., 2005; Lambrich and Schubert, 2005). The specific role and choice of food ingredients in the stabilization (and controlled destabilization) of emulsions will be discussed in the section “Release Triggers for Emulsions.” The most important rule of food emulsion production is that the emulsion should initially be stable. Emulsions are kinetically rather than thermodynamically stable two-phase systems and, ultimately, both oil and water phases will separate. To understand how to optimize emulsion stability, it is necessary to understand the mechanisms by which emulsions are destabilized. There are four main mechanisms whereby emulsion phase separation may be accelerated. These are summarized accordingly. Creaming/Sedimentation For most food emulsions, the oil phase has a lower density than the aqueous phase and can thus separate out due to gravity. For o/w-type emulsions, creaming specifically refers to the motion of emulsion droplets under gravity to form a concentrated creamy layer at the top of the emulsion. Whether or not there is a change in droplet size in this highly concentrated region depends on the stability of the droplets against coalescence. Creaming of poorly stabilized emulsions may result in complete breaking of the emulsion layer, resulting in phase separation. For well-stabilized emulsion droplets even an extensively creamed layer can be fully re-dispersed. For w/o-type emulsions, the movement of droplets under gravity is referred to as sedimentation. The rate of creaming for an individual noninteractive spherical droplet, s, can be defined for highly dilute emulsions through Stokes’ Law: S

(

)

2 r 2 ρ0 ρ g 9η0

where g is the acceleration due to gravity, r is the radius of the droplet, is the density of the dispersed phase, 0 is the density of the continuous phase and 0 is the Newtonian shear viscosity of the continuous phase. From this equation it can be seen that the rate of creaming can be reduced by: • Reducing droplet size—homogenization of milk typically reduces droplet size from ca. 4 μm in diameter to <1 μm in diameter resulting in a considerable improvement in creaming stability of the milk.

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• Increasing the viscosity of the continuous phase. • Density matching the continuous and dispersed phases. From a quantitative perspective, the Stokes’ equation applies only to highly dilute, noninteracting emulsions and is therefore not applicable to concentrated, polydisperse or aggregated emulsion systems. However, the parameters governing creaming rate, as defined by the Stokes’ equation, can of course be applied nonquantitatively to improve creaming stability. The simplest way to measure creaming is by direct observation. However, this relies on the formation of a well-defined layer between cream-rich and cream-depleted regions. Where there is a more diffuse concentration gradient, it may be impossible to directly or accurately detect when creaming is occurring. There are several commercially available techniques that can be used to provide a more accurate analysis of emulsion creaming. These include ultrasound, magnetic resonance imaging and conductivity. The advantage of these techniques is that they are noninvasive and can provide a reasonable approximation of changes to dispersed phase volume across a sample (Dickinson et al., 1994; Dickinson, 1996). Flocculation Flocculation is a general term referring to the various mechanisms for aggregation or association of droplets whereby the interfacial layer of the droplets remains intact (Dickinson, 1998). Generally, for dilute emulsions, flocculation results in enhanced creaming, since the flocs structures rise more quickly under gravity relative to individual droplets. However, in more concentrated emulsions, it is possible that flocculation can lead to the formation of a percolating network, which can be controlled to manipulate both stability and rheological properties of the emulsion (Chanamai et al., 2000; Dalgleish, 2006). Flocculation of emulsion droplets takes place when the pair-interaction free energy becomes appreciably negative at a particular separation. This can be achieved through a number of different mechanisms of varying interaction potential. These are briefly summarized. Depletion flocculation This is encountered in emulsion systems containing suitable depletants such as noninteracting polysaccharides (e.g. xanthan) or micellar species (e.g. SDS or sodium caseinate) and recently reported to take place in bimodal emulsions, where there is an adequate difference between distributions (Dickinson and Golding, 1997a; Moschakis et al., 2005; Djerdjev et al., 2006). Depletion takes place due to the entropic exclusion of the depletant as droplets approach each other. Due to the exclusion of the depletant, an osmotic pressure gradient forms between droplets resulting in a net attraction thereby leading to flocculation. The strength of the interaction potential is proportional to the sizes of both droplets and depletant as well as the relative concentration of the depletant. Depletion flocculation is termed weak or reversible flocculation, since flocs can be broken up by simple shaking. However, even though the interaction is weak, depletion can result in extensive aggregation of droplets leading to rapid creaming and separation in the case of dilute emulsions, or greatly increased viscosity in the case of more concentrated emulsions.


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Bridging flocculation Bridging flocculation is a general term to describe the association of emulsion droplets through interfacial interaction. The strength of the interaction depends greatly on the specific nature of the bridging mechanism, which are discussed below. Electrostatic bridging: Droplets stabilized by charged interfacial layers can be bridged through the addition of a species containing counterions. This can be achieved through the addition of an appropriate salt or of a charged biopolymer with the capability of multiple binding sites. Salt bridging requires a minimum divalent ion to enable bridges to form between droplets. An example is the calcium-ion bridging of a casein-stabilized emulsion at neutral pH. In this case, the divalent calcium is able to bind to negatively charged amino acids on the peptide chain of the protein adsorbed onto the interface. This can result in interfacial cross-linking between droplets or cross-linking between droplets and free protein in the continuous phase (Dickinson and Golding, 1998; Ye and Singh, 2001). Alternatively, a biopolymer with opposite charge to the interfacial layer can also behave as an electrostatic bridging link between droplets (Bratskaya et al., 2006). Taking an adsorbed casein interface as an example, at neutral pH, where the net charge at the interface is negative, and a cationic biopolymer will be required to form electrostatic cross-links. (Note: There are very few cationic biopolymers available within the foods industry. Examples include acid/high pI gelatin and chitosan.) However, at pH below the pI of the protein, where the net surface charge is cationic, electrostatic cross-links can be formed using an anionic biopolymer (such as pectin or carrageenan) in the aqueous phase. Electrostatic bridging flocculation provides a stronger inter-droplet interaction relative to depletion, although high shear can be used to break up aggregated structures. Incomplete surface coverage bridging: This takes place for emulsions stabilized by higher molecular weight emulsifiers, such as proteins. For emulsion droplets to possess good stability, an adequate surface coverage of the droplet surface is required. If no sufficient emulsifying material is present to provide good coverage, it is possible that biopolymer molecules will become adsorbed to more than one droplet surface, leading to bridging flocculation (Dickinson and Golding, 1997b). A similar effect can be observed when emulsions are homogenized at very high pressures. Under these circumstances, protein can become adsorbed to more than one droplet surface during homogenization, leading to the formation of an inter-connected protein network. Covalent bridging: Droplets stabilized by biopolymer interfaces can also be cross-linked through covalent bridging mechanisms (Dickinson, 1997; Romoscanu and Mezzenga, 2005). There are several routes by which covalent cross-linking can be induced. For example, covalent cross-linking can be thermally induced for protein-stabilized emulsions whereby the adsorbed layer contains accessible disulphide peptides capable of intermolecular cross-linking. The use of high static pressure treatments can also act in a similar manner to induce disulphide cross-linking for appropriate globular protein-stabilized emulsions (Galazka et al., 2000). Enzymatic covalent cross-linking: This is another mechanism by which droplet bridging may take place. One example is the use of the microbial enzyme transglutaminase, which catalyses covalent cross-linking between lysine and glutamine amino acids. Consequently, adsorbed protein interfacial layers which display good availability and accessibility of these two amino acid residues (such as the casein proteins) may become covalently cross-linked. For covalent cross-linking to take place, droplets must be in close proximity. Consequently, for dilute emulsions cross-linking may not occur (or interaction with

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cross-linking species present in the continuous phase may take place). At higher dispersed phase volumes, where droplet–droplet separation is sufficiently low for cross-linking to happen, bridging mechanisms tend to result in the formation of a droplet network (Dickinson and Yamamoto, 1996). In this respect, bridging flocculation is used more as a structuring pathway to create emulsion-based gel systems rather than as a cause of instability, per se. Coalescence Coalescence of emulsion droplets occurs when there is film rupture at the interfaces of adjoining droplets. This leads to the irreversible conjoining of the droplets into a single larger entity. Catastrophic coalescence, such as may take place in a homogenized emulsion in the absence of emulsifier or for poorly stabilized emulsions, can rapidly lead to breaking of the emulsion and partitioning into separate (free) oil and aqueous phases. Where more limited coalescence takes place (such as through controlled shear), the emulsion can then become unstable due to gravity forces enhancing the creaming rate of the larger droplets. For film rupture to take place there must be sufficient film thinning between droplets. Film thinning depends on the relative hydrodynamics within the film, and is dependent on a number of factors, such as the rheological properties of the continuous phase, the concentration of the dispersed phase and the effective stabilization of the droplets and their ability to maintain appreciable inter-droplet distance. Interfacial rupture depends on the mechanical properties of the film and the influence of shear and temperature. Emulsion droplets can be stabilized through adsorption of a viscoelastic and/or charged interface, which is often the case with adsorbed protein, or alternative biopolymer layers. Increasing interfacial viscoelasticity can provide effective droplet stability against coalescence, even at high applied shear forces. Crystalline interfaces can also provide surface rigidity and effective stabilization against coalescence (Dickinson et al., 1988; Simovic and Prestidge, 2004; Giermanska-Kahn et al., 2005; Tcholakova et al., 2005). Emulsions stabilized with small molecule surfactants do not possess viscoelastic or charge-stabilized (in the case of nonionic emulsifiers) interfaces. For such systems, stability against coalescence is provided through the Marangoni effect, in which surfactant streaming at the point of film thinning leads to an osmotic pressure differential between the film and the surrounding solvent. Consequently, water is drawn into the film gap, thereby preventing further thinning from taking place. An intermediate state of coalescence, termed partial coalescence, is often utilized in the food industry to deliberately induce fat structuring in a number of products, such as ice cream, whipping cream and spreads. In such cases, the interface of the emulsion is designed through formulation, such that it will rupture under appropriate conditions, thereby resulting in coalescence of the emulsion. However, for emulsion systems where the dispersed phase contains a prerequisite level of solid fat, the presence of the solid fat can prevent formation of a single larger entity. Instead, fat droplets form agglomerated structures, sharing a common interface, but in which a degree of the original droplet integrity is maintained. The formation of such agglomerated structures is used to improve the quality of aerated products such as whipped cream and ice cream, by improving the stability of foam structures and reducing drainage (Vanapalli and Coupland, 2001; Coupland, 2002; Hotrum et al., 2005).


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Ostwald Ripening Ostwald ripening is essentially the growth of larger emulsion droplets at the expense of smaller ones. It may happen in polydisperse emulsions, and takes place due to the fact that the solubility of the oil phase increases with decreasing droplet size. For small droplets this increase in solubility may allow the oil to dissolve and diffuse through the aqueous phase, condensing into larger droplets where solubility is lower. It is difficult to see how the mechanism could be exploited for encapsulation and controlled release; however, for the interested reader additional information can be found in the literature (Taylor, 1998; Hoang et al., 2004; Meinders and van Vliet, 2004; Mun and McClements, 2006). This section on “Emulsion stabilization” is aimed to highlight the various mechanisms by which emulsions can be destabilized. These are represented in Figure 3.1. Before going on to explore potential routes for formulating food emulsions, it is important to remind ourselves that use of emulsions for controlled delivery and release depends primarily on two things: first, the necessity to stabilize the emulsion against separation prior to delivery; and, secondly, to control destabilization of the emulsion using one or more of the above instability mechanisms to achieve the required release and delivery under the appropriate physiological conditions.

Formulation Design for Food Emulsions One of the more obvious constraints on the formulation of food emulsions is that all components should be edible, food-grade and approved for use by international legislation. Two approaching colloidal particles

Attractive forces highly dominate Interaction between particles van der Waals, electrostatic, steric, depletion Coagulation Hard spheres

Partial coalescence Solid/liquid Repulsive forces dominate Stable

Coalescence Emulsions Attractive forces dominate Flocculation

Figure 3.1.

Schematic representation of mechanisms for droplet stabilisation and instability.

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Whilst this places certain restrictions on the scope of formulation, it has led to considerable creativity with regard to the application of these ingredients for food structuring. The formulation of a food emulsion needs to be considered from three perspectives: the design of the aqueous phase, the nature of the dispersed phase and the composition of the interface. The choice of formulation also depends on whether the emulsion is intended to be o/w or w/o (or on occasion w/o/w or o/w/o). For an o/w-type emulsion, options for formulation can be summarized as below. Design of the Aqueous Phase There are two important aspects to consider when formulating the continuous phase of an o/w food emulsion. The first is microbiological stability, which can be tailored according to the anticipated shelf life of the product. This has less relevance to encapsulation and controlled release, although it is important to note that for products designed with a long closed shelf life in mind (>3 months), there should be no change in the emulsion structure, to ensure that the release properties remain consistent over the lifetime of the product. Microbiological stability can be improved through both thermal treatment (pasteurization/sterilization) and aseptic packaging. In addition, emulsions prepared at low pH (<4), high sugar or alcohol content, with low water activity, or containing preservatives will all have improved microbiological stability. The second point of consideration is that manipulation of the continuous phase can have a significant impact on the rheological properties of the emulsion. This can have important consequences on delivery, both in terms of oral response behavior of the emulsion and for the subsequent behavior in the GI tract. Continuous phase properties are very much dependent on product type. For example, beverage emulsions are generally low in viscosity, and while it is necessary that the dispersed phase remains stable, there is little requirement for the addition of thickeners or stabilizers. In contrast, a reduced fat mayonnaise requires the addition of aqueous thickeners to the continuous phase in order to compensate for reduced viscosity through the removal of fat. Whilst the addition of biopolymers, such as starch and guar gum, can be used to control aqueous phase rheology independently of the dispersed phase, biopolymer addition can also result in additional rheological manipulation through structuring of the fat phase. This may take place through such effects as depletion flocculation, bridging flocculation or phase separation, and are discussed in the section “Emulsion Stabilization.” A summary of a number of biopolymers available for aqueous phase structuring is given in Table 3.2. This list is not comprehensive and ignores any synergistic effects that may exist for combinations of biopolymers. As can be seen from Table 3.2, a number of functional effects can be achieved through aqueous phase structuring. Depending on the nature of structuring, and the potential for aqueous phase biopolymers to interact with the dispersed phase, it is possible to control the release properties of the emulsion, both in terms of emulsion structure failure in mouth (textural response and taste/flavor release) and in terms of emulsion separation under gastric conditions. Examples of how continuous phase behavior can influence release properties will be given in more detail in the sections “Delivery of Water-Soluble Food Actives via Emulsions” and “Delivery of Hydrophobic Food Actives via O/W Emulsions.”


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Table 3.2.

Examples of aqueous phase structuring ingredients

Biopolymer type

Biopolymer name

Effect

Polysaccharide

Guar Pectin (low/high methoxy)

Thickener, stabilizer Stabilizer, thickener, gelling

Xanthan Carrageenan Locust bean gum Starch (modified) Casein (SMP) Casein (SMP, caseinate)

Thickener, yield stress Thickener, stabilizer, gelling Thickener, gelling (cryogelation) Thickening, gelation (heat set, cold set) Thickening, gelation (acid) Gelation (enzyme)

Whey Soy Gelatin Egg (ovalbumin)

Gelation (thermal, covalent) Gelation (thermal, covalent) Gelation (thermal, coil-helix transition) Gelation (thermal, covalent)

Starch Protein

a Under

49

Interaction with dispersed phase None Electrostatic bridginga and depletion Depletion Bridginga None None Bridginga Bridginga, depletion Bridginga Bridginga Bridginga Bridginga

appropriate interfacial conditions.

Choice of Lipid Phase Many fats and oils are available for use in food emulsions. Whilst the main role of fat in a food product is sensoric, from a product design perspective the use of a particular fat/oil or blending of different lipids can have a significant impact on food emulsion properties. A summary outlining examples of fat types and their composition is given in Table 3.3. Generally a food fat is any triglyceride composition which is solid at room temperature, whilst oil is liquid. For many food emulsions, where the emulsion has been designed to provide structure, solid or hardened fats are often used. Typical examples include ice cream and whipping cream, where the solid fat droplets are able to stabilize air bubbles in the product, as well as generating structure through partial coalescence. This form of fat structuring improves product quality through improved stabilization of the air phase and a slower rate of melt. Saturated fats are also utilized extensively in the spreads and margarine industry, where required crystallization is an essential aspect of continuous phase structuring and stabilization for w/o-type emulsions. For both these examples it would be impossible to use unsaturated fats to achieve this degree of structuring. In contrast, a product such as mayonnaise uses liquid oils, since it would be impossible to achieve the correct sensory properties with a hardened fat. In addition to structuring, another functional use of the oil phase for an o/w emulsion is as a carrier for lipophilic actives such as flavors, nutrients (e.g. oil-soluble vitamins) and colors. Design of the emulsion system is important for how these actives are stabilized in product and how they are released on consumption. The technical challenges associated with the delivery of lipophilic actives will be discussed in more detail, with examples in the sections “Delivery of Hydrophobic Food Actives via O/W Emulsions” and “Delivery of Dietary Fats as O/W Emulsions and Their Protection against Oxidation”. It should also be noted that w/o and water-in-oil-in-water (w/o/w) type emulsions can be utilized in a similar manner for the controlled delivery and release of water-soluble actives such as vitamins and enzymes.

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Table 3.3. Examples of common food fats and oils and their melting points (MP) and fat composition (in %). Saturated fatty acid chains of a given chain length are given the suffix Cxx:0, whilst unsaturated fatty acid chains are given the suffice Cxx:1/2/3 depending on the degree of unsaturation

Fat or oil Butter fat Lard oil Castor oil Cocoa butter Coconut oil Corn oil Cottonseed Olive oil Palm oil Palm kernel Peanut Rapeseed Safflower Sesame oil Soybean Sunflower seed

Other Other (satu(unsatuMP (°C) C12:0 C14:0 C16:0 C18:0 C20:0 rated) C16:1 C18:1 C18:2 C18:3 rated) 32.2 30.5 −18 34.1

2.5 – 0.6 –

11.1 1.3 0.6 –

29 28.3 0.6 24.4

9.2 11.9 0.6 35.4

2.4 – – –

4.8 – – –

4.6 – – –

26.7 74–76 7.4 38.1

25.1 −20 −1 −6 35 24.1 3 −10 – −6 −16 −17

45.4 – – – – 46.9 1.92 – 1.1 – 0.2 –

18 1.4 1.4 Trace 1.4 14.1 2 – 1.1 – 0.1 –

10.5 10.2 23.4 6.9 40.1 8.8 1.4 1 1.2 9.1 9.8 5.6

2.3 3 1.1 2.3 5.5 1.3 1.9 – 1.1 4.3 2.4 2.2

0.4 – 1.3 0.1 – – 2.4 – 1.2 0.8 0.9 0.9

14.6 – – – – 9.7 – – – – – –

0.4 1.5 2 – – – – – – – 0.4 –

7.5 49.6 22.9 84.4 42.7 18.5 17.8 32 18.6 45.4 28.9 25.1

3.6 – 3.1 2.1

– – – –

8.5 – 87 –

Trace 34.3 47.8 4.6 10.3 0.7 – 15 70.1 40.4 50.7 66.2

– – – – – – 17.5 1 3.4 – – –

– – – – – – – 50 – – – –

Finally, it should be noted that the choice of fat/oil is also important from a nutritional perspective. Generally, highly saturated fats can have a negative impact on health. Oils with high polyunsaturated triglyceride content are considered preferential in terms of dietary intake, and that oil-containing ω-3 fatty acids are often quoted within nutritional literature as imparting specific health benefits when consumed regularly. However, replacing all saturated fats with polyunsaturated oils is not a trivial exercise. As has been mentioned, the degree of saturation can have an impact on the structuring behavior of the emulsion. In addition, highly unsaturated oils are prone to oxidation, which can lead to the development of adverse odors and flavors. Inhibition of oxidative processes within emulsion systems remains one of the key challenges in the move towards a healthier diet, and will be discussed in more detail in the section “Delivery of Dietary Fats as O/W Emulsions and Their Protection against Oxidation.” Interfacial Formulation and Design Arguably the most important aspect of emulsion preparation is the composition of the interface. Of course, the number of ingredients available for formulation of food emulsions is limited to what can be considered edible and food-grade, and may vary between countries depending on legislation. However, food emulsifiers can broadly be characterized into two categories: low molecular weight species based on fatty acids and high molecular biopolymers with amphipathic properties. Examples of food emulsifiers are given in Table 3.4. For all food products, choice of emulsifier is a key to achieving the desired textural and sensory properties. The design of the interface will also play a controlling role in the


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Table 3.4. Summary of some food emulsifiers available for stabilization of oil-in-water and water-in-oil food emulsions, including application

High-molecularweight biopolymer

Name

Type

Functionality

Application

Skimmed milk powder

Dairy protein

O/W emulsion stability at neutral pH, emulsion structuring (bridging) at acid pH O/W emulsion stability at neutral pH, emulsion structuring (bridging) at acid pH O/W emulsion stability at neutral pH, emulsionbased gels under thermal processing Encapsulation, emulsionbased gels O/W emulsion stability at low pH O/W emulsion stabilizer

Ice cream, yoghurt

Sodium caseinate Dairy protein

Whey powder

Dairy protein

Gelatin

OSA starch

Bovine/Porcine/ Fish Protein Polysaccharide galactan protein Modified starch

Lecithin

Phospholipid

Gum arabic

Low-molecularweight emulsifier

Monoglycerides

Glycerol-esterified fatty acids and triglycerides Sodium stearoyl Lactic acidlactylate esterified monoglyceride Datem Diacetyl tartaric acid-esterified monoglyceride Tween Polysorbateesterified triglyceride PGPR Polyglycerolesterified monoglycerides

Cream liqueurs, meat emulsions

Neutral pH beverages, infant formulations Nutritional supplements Acid beverages Acid beverages

O/W and w/o stability depending on modification W/O emulsion stabilization and o/w destabilization O/W emulsion stabilization

Spreads, mayonnaise

O/W emulsion stabilization

Powder mixes, gravy

O/W emulsion stabilization, destabilization W/O emulsion stability

Desserts, ice cream, dressings

Spreads, ice cream, cream liqueurs Salad dressings, creamers

Spreads and other oil continuous products

stabilization and breakdown of emulsion structure. High molecular weight amphipathic biopolymers, in particular milk proteins, are very effective at stabilizing o/w-type emulsions. Here, adsorption of casein and whey protein onto the oil–water interface provides effective steric and electrostatic stabilization against coalescence and flocculation. Most dairy-based food emulsions, such as milk, dairy and nondairy creams, ice cream and yoghurt are based on milk protein stabilization of the emulsion. The advantages of using proteins are the nutritional and clean-label aspects associated with proteins. In addition, caseins (essential milk protein fraction) are able to maintain functionality as a result of thermal processing. The disadvantage of proteins is that the peptide interface can be sensitive to changes in pH and ionic composition. For example, acidification of the emulsion towards the isoelectric point of the protein or addition of calcium ions can result in flocculation of the emulsion. In some instances this results in undesirable separation of the emulsion. However, aggregation of dairy emulsions

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through pH and calcium is also deliberately used for specific product design, such as in the manufacture of yoghurt or cheese. Where pH sensitivity is an issue for emulsion stability, alternative emulsifiers are available. In particular, for beverage emulsions, where the dispersed phase is dilute and requires effective stabilization, gum arabic or modified starch can be used. In both cases, the structure of the biopolymer allows for effective interfacial stabilization, even at low pH. Low molecular weight emulsifiers do not have the clean-label perception of proteins. However, they are often able to bring specific functional benefits not achieved by proteins alone. Most low molecular weight emulsifiers are based on triglycerides or fatty acids that have undergone an esterification process to produce amphiphilic molecules, whereby the fatty acid chain provides the hydrophobic tail group and the esterified species (such as glycerol) provides the more hydrophilic headgroup. Depending on the chain length, degree of (un)saturation of the triglyceride, and the type of headgroup, the amphiphilic properties of emulsifiers can be controlled to a certain degree. This classification of emulsifiers according to their amphiphilic properties is known as the hydrophilic–lipophilic balance (HLB). HLB is a numerical scale for emulsifiers. Emulsifiers which are more hydrophobic in nature have low HLB values. Increasing hydrophilicity increases HLB score. For example, polyglycerol polyricinoleate (PGPR), which is a hydrophobic emulsifier used for the stabilization of w/o-type emulsions, has an HLB value of 2. In contrast, polysorbate emulsifiers, which are commonly used for the stabilization of o/w emulsions, have HLB values of around 16. The choice of an emulsifier for a product is very much dependent on the required functionality imparted by the emulsifier. Emulsifiers are mainly used for emulsion stabilization as well as its controlled destabilization in food products. Other uses include functional applications such as fat crystal modification, aeration, wetting, and the formation of stable mesophases. The other main application of emulsifiers, often but not always in combination with emulsion systems, is as delivery vehicles for active components. The use of interfacial design for both biopolymer- and emulsifier-stabilized interfaces will be discussed in more detail in subsequent sections.

Release Triggers for Emulsions To be able to design food emulsions for encapsulation and delivery, it is necessary to identify where and how delivery will take place. For delivery of actives that are intended to impart a sensory benefit of the product, delivery takes place on consumption. Behavior of the active in-mouth is therefore of considerable importance. Mouth is a remarkable receptor for sensory perception. Our preference or dislike for certain foods and drinks is driven by three key attributes: 1. Taste and aroma perception. 2. Texture perception: design of food microstructure is responsible for the initial textural perception of a foodstuff. 3. Our like or dislike of a food may derive not only from the initial texture of the product but also from the way in which it breaks down in the mouth. Consequently, when designing food structure, it is necessary to take into account the manner in which the product microstructure breaks down on eating. This is often an issue for fat replacement in foods. It may be possible to replace the fat in a product with aqueous fillers such as


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starch, such that the initial rheological properties of the two products are the same. However, the breakdown of the two different structures during mastication may result in the two products being texturally perceived entirely differently. The breakdown of microstructure in the mouth will also influence both taste perception and flavor perception. The breakdown of food structures in the mouth is dependent on the applied shear forces during mastication, dilution of the structure with saliva and the fact that in-mouth temperature is generally higher than ambient temperatures ex-vivo. In addition, amylase present in saliva will rapidly start the digestion of starch in the mouth, which may impact on texture. Physical changes in microstructure on eating, such as melting point transitions (fat, gelatin), phase inversions (w/o to o/w emulsions), break-up of aggregated emulsion structures, can not only influence textural response, but also be used to control the release of actives, such as tastants or flavors, in the mouth. Alternatively, delivery of an active for nutritional benefit will need to take place after consumption. Consequently, the release properties of the emulsion/active under gastric conditions will be paramount. In the GI tract, emulsions face a low pH (around 2.0) and pepsin in the stomach and lipases and bile salts in the beginning of the small intestine. Lipophilic actives may then be absorbed by the human body in the intestine via dietary micelles. Furthermore, since nutritional actives often possess negative taste attributes (e.g., bitterness or astringency), there may also be the additional requirement that release of the active inmouth should be minimized as much as possible and that the active should be encapsulated in such a way that it is undetectable on consumption. Clearly, in designing emulsions with particular delivery and release properties, the physiological conditions of the delivery site will need to be taken into consideration. For inmouth and gastric conditions the delivery environment will be quite different.

Delivery of Water-Soluble Food Actives via Emulsions Water-in-Oil Emulsions for Controlling Water-Soluble Actives Most spreads containing 40% or more fat are fat-continuous products with the aqueous phase being dispersed as w/o emulsions. One of the key requirements for a good spread is phase inversion during breakdown in the mouth (see also “Release Triggers for Emulsions”), thereby releasing, for example, salt. Margarines that do not do that are perceived as waxy and with very little taste. In principle, stable w/o emulsions that do not invert in the mouth should be able to trap, for example, bitter hydrophilic molecules (such as proteins) in the water phase without being perceived.

Effect of O/W Emulsions on Taste Release and Perception In foods containing both water and lipids, the lipid phase may also take part in the sensory perception by influencing the distribution of food components in the oil and aqueous phases or at the oil—water interface (Yamamoto and Nakabayashi, 1999). Similarly, fats can modify the perception of other sapid food components by influencing their partitioning between the food matrix, saliva, taste receptors (for taste), or headspace (for aroma) within the oral cavity (Forss, 1973). Traditionally the majority of flavor studies in emulsion-based

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foods have focused on aroma release and little has been reported on the effect of fat on taste perception. Shamil and co-workers (1991) found that the reduction of fat in cheese led to an increase in bitterness and astringency and a reduction in saltiness. Increased bitterness and astringency were assumed to arise from the hydrophobic character of these ingredients and the resultant increase in their concentration in the aqueous phase when the fat level was reduced. Conversely, the decrease in salt intensity when the fat level was reduced was proposed to be due to the reduced concentration of salt in the aqueous phase. Wendin (Wendin, et al., 1999) also reported that a decrease in fat content led to a decrease in sour taste due to the reduced concentration of the acid in the aqueous phase. Earlier studies have shown a correlation between oil mouth coatings and taste perception (Lynch et al., 1993). Valentova and Pokorny (1998) also found that the intensity of sweet, bitter, and astringent compounds was reduced by the prior consumption of oil, but acidic and salty tastes were not affected. Lynch and co-workers (1993) found that all the taste modalities were affected, albeit by a small amount, and that coconut oil had a more suppressive effect than sunflower oil and proposed that fat mouth coatings physically interfere with tastant access to the taste receptors. Yamamoto and Nakabayashi (1999) concluded from their work on the effects of increasing oil-phase volume on salt perception in o/w emulsions that taste intensity will be influenced by a combination of an increased concentration of salt in the aqueous phase and a suppressed contact of salt with taste receptors. Overall, however, the results cited in the literature on the effects of oil on tastants have been inconclusive but suggest that oils and emulsions can influence taste perception. The taste-modifying effects of fats may be mediated through: 1. Changes in the partitioning of flavor (taste) compounds between the food (e.g., changes in the aqueous phase concentration as the fat level is altered), saliva and the taste receptor cell membranes and pores. 2. Physical interference with diffusion processes affecting access or binding of taste molecules to receptors through a mouth coating action by the oil. 3. Changes in the rate of regeneration of interfacial surfaces required for the release of sapid compounds into the surrounding media. In order to test these ideas, Malone et al. (2003) investigated the relationship between taste perception and microstructure and specifically the effect of fat content in o/w emulsions on salt perception. Their studies involved a sensory analysis of salt perception on isoviscous o/w emulsions with fat contents ranging from 0 to 95%. The results showed that as the fat content was increased for products kept at constant salt concentration, the perceived saltiness increased due to the associated increase in the salt concentration in the aqueous phase (Figure 3.2). However, when the salt concentration on aqueous phase was kept constant the saltiness decreased with increasing fat content (Figure 3.2), suggesting that perceived saltiness is nonlinearly dependent on a combination of salt concentration and aqueous phase volume. Based on their results a psychophysical model was developed that related taste intensity to salt concentration and the phase volume of fat: I k [C ]np (φaq )n [1 exp(mφaq )]


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Figure 3.2. Effect of oil phase volume in o/w emulsions on salty taste perception for constant salt concentration on product or on aqueous phase.

where I is the taste intensity, k is a constant, n is a power-law number, Cp is the concentration of tastant on product, aq is the aqueous phase volume and m is the amount of tastant in the aqueous phase. Indeed, through this insight, water-in-oil-in-water duplex emulsions have been designed to control taste perception by effectively controlling the extent to which the aqueous phase is able to interact with the oral surfaces (further described in the section “Control of Taste Using W/O/W Emulsions”).

Double Emulsions for Controlling Water-Soluble Actives Double emulsions (also known as “duplex emulsions”) have potentially promising applications in the food industry, primarily for sustained release of active components via a controlled transport mechanism (Matsumoto and Kang, 1989; Garti, 1996, 1997a, 1997b, 1998; Garti and Aserin, 1996a, 1996b; Garti and Bisperink, 1998; Garti and Benichou, 2001), for taste masking (Malone et al., 2003) and for encapsulating sensitive ingredients such as flavors and active components (Kim and Lee, 1999; Yoshida et al., 1999; Edris and Bergnståhl, 2001; Benichou et al., 2004; Onuki et al., 2004; Shima et al., 2005) in both the water and oil phases (van der Graaf et al., 2005). Two main types of double emulsion can be distinguished: w/o/w emulsions, in which a w/o emulsion is dispersed as droplets in an aqueous phase, and oil-in-water-in-oil (o/w/o) emulsions, in which an o/w emulsion is dispersed in an oil phase. This latter emulsion is less common primarily due to having few hydrophobic emulsifiers that are food-grade to stabilize water droplets in continuous oil phase (Pays et al., 2002). The advantage of double emulsion technology is in their double compartment structure, in which they act as reservoirs, encapsulating a range of active components. Actives that are water-soluble but insoluble in the oil phase can be entrapped in w/o/w emulsions, and actives that are oil-soluble but insoluble in the water phase can be entrapped in o/w/o emulsions. Actives that are both soluble in oil and water cannot be “encapsulated.” The encapsulated actives may be released subsequently under variable conditions. This will be the main topic covered in this section, although the production and the issues of instability will also be addressed briefly.

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Production of W/O/W Emulsion Membrane emulsification is one of the key technologies for producing stable double emulsions due to the prevailing mild shear stress conditions (van der Graaf et al., 2005). Usually double emulsions are prepared in a two-step emulsification process using two surfactants: a hydrophobic surfactant to stabilize the internal w/o emulsion and a hydrophilic one for the external interface of the oil drops with the aqueous environment. In conventional emulsification processes high shear stresses are needed to reduce the internal droplet size and droplet size distribution of the emulsion, but this also causes internal streaming in the droplets, which causes more collisions and therefore coalescence of the internal water phase with that of the outer aqueous phase (Muguet et al., 1999; Klahn et al., 2002). Membrane emulsification (Nakashima et al., 1991) is a relatively new method for producing double emulsions but has added benefits in its low energy consumption, better control of the droplet size and distribution and mildness of processing. In general two methods are used: cross-flow membrane emulsification and pre-mix membrane emulsification (Suzuki et al., 1998). In the latter case a pre-mix is forced through a membrane, which further breaks up the droplets. In the cross-flow method the to-be-dispersed phase is pressed through a microporous membrane while the continuous phase flows along the membrane surface. Once this primary emulsion is produced, the second emulsification step to produce the o/w/o emulsion can also be carried out using membrane emulsification, which helps prevent rupture of the double emulsion and inversion into a single o/w emulsion. Membrane emulsification for the production of single emulsions has been reviewed by a number of authors (Joscelyne and Tragardh, 2000; Charcosset et al., 2004) and for microstructured emulsion systems by Lambrich and Vladisavljevic (2004). Gijsbertsen-Abrahamse et al. (2004) reviewed the current status of membrane emulsification and van der Graaf et al. (2005) have recently reviewed membrane emulsification techniques for the production of w/o/w emulsions and also highlighted new developments in nanoengineered and microengineered membranes, such as microsieves to improve the flux of emulsions through the membrane (van Rijn, 2004). Instability of W/O/W Emulsions The main problem with double emulsions though is that they tend to be unstable since they contain more interface and therefore are more thermodynamically unstable than single emulsions. Much literature has been published on this subject since around the mid-1980s (Garti et al., 1994; Garti and Aserin, 1996a, 1996b). Florence and Whitehill (1981) described four possible mechanisms for instability of w/o/w emulsions: 1. 2. 3. 4.

Coalescence (see “Coalescence”) of the internal aqueous droplets Coalescence of the oil droplets Rupture of the oil film separating the internal and external aqueous phases Migration of water (including the water-soluble ingredients) between the internal and external water phases through the oil layer.

This migration of the water phase discussed above could be via reverse micellar transport; by diffusion across the oil layer, where it is at its thinnest; and transport via hydrated surfactant (for further details see “Transport and Release Mechanisms of Water-Soluble Components”).


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An enormous amount of formulations for double emulsions is known in the literature with various types of oil, different fractions of phases and different sorts of surfactants in varying concentrations (van der Graaf et al., 2005). Several methods have been documented in the literature for improving stabilization and slowing solute release (Davis et al., 1985). The methods can be categorized into three main areas: 1. Stabilization of the internal interface of the inner emulsion 2. Selection of appropriate oil phase and components that could structure it and 3. Stabilization of the outer interface. A range of low molecular weight emulsifiers, oils, co-solvents and co-emulsifiers have been tried (Benichou et al., 2004). Materials that have been investigated also include biopolymers, synthetic graft and comb co-polymers and polymerized emulsifiers that impart steric or mechanical stabilization. Monomeric nonionic emulsifiers (hydrophobic and hydrophilic) have some limitations in terms of emulsion stability and therefore other molecules such as naturally occurring macromolecular materials (e.g., gums and proteins) are of interest (Garti, 1997a, 1997b). Macromolecules such as proteins offer excellent stabilization effects through electrostatic repulsion in combination with steric contributions. Proteins, polysaccharides and their blends are natural surface-active biopolymers. Under appropriate conditions these may complex through electrostatic interaction, and the newly formed macromolecular amphiphile can anchor onto oil–water interfaces more strongly (Benichou et al., 2002). Complexation between proteins and polysaccharides at the emulsion droplet surface can improve steric stabilization. Droplet size can be smaller if the polysaccharide is present during homogenization, and so rate of creaming may be reduced so long as there is no bridging flocculation (Benichou et al., 2002). Combinations of surfactants in the outer water phase have also shown a beneficial effect on stability and these multianchoring flexible amphiphilic surfactants are effective emulsifiers since they can improve the steric stabilization by forming thick multilayered coating on the emulsion droplets and also by providing protection against coalescence by making them resistant to shear (Garti, 1998). Transport and Release Mechanisms of Water-Soluble Components Two major release mechanisms involved in the release of a water-soluble active such as common salt (NaCl), which is entrapped in the aqueous core of w/o/w double emulsions, have been suggested (Pays et al., 2002). The first one describes the rupture of the thin liquid film separating the internal droplets and the double emulsion surfaces. The second is when the entrapped species diffuses or permeates through the oil membrane. These two mechanisms can be controlled by varying the composition and amounts of surfactant in the system. In w/o/w emulsions stabilized with sodium dodecyl sulfate below its critical micelle concentration (cmc), the release of salt occurs by diffusion across the oil membrane. Water transport also needs to be taken into account and a number of mechanisms have been suggested (Wen and Papadopoulos, 2000, 2001): through the surfactant thin lamellae, by reverse micelles and via hydrated surfactant. Ficheux et al. (1998) identified two types of thermodynamic instabilities that allow the (uncontrolled) release of entrapped actives. The first mechanism involves the coalescence of the inner and outer aqueous phase, through the

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rupture of the thin nonaqueous film between them, so that inversion to a single emulsion occurs. This mechanism is best suited for the release of water-soluble components, and the release kinetics can be controlled by the hydrophilic surfactant concentration. Depending on the concentration of surfactant, double emulsions may be destabilized with a time scale ranging from a few months to a few minutes. The second mechanism involves the coalescence between the smaller droplets inside the oil phase leading to an increase in the internal droplet size and a reduction in number. Interestingly, even if the osmotic pressure is balanced between the internal and external phase, electrolytes can still be transported out through the reverse micellar mechanism, which is controlled by the viscosity of the oil phase and the nature of the oil membrane (Garti and Bisperink, 1998). The release rate from double emulsions in general tends to follow first-order kinetics (Garti et al., 1994; Sela et al., 1995; Jage-Lezer et al., 1997) with the release rate being controlled primarily by an increase in the diffusion of the active through the oil phase by the selection of appropriate secondary hydrophilic emulsifiers. Delivery of hydrophilic actives in the GI tract has also been studied with w/o/w emulsions (see “General Applications of W/O/W Emulsions”). The oil layer is supposed to protect the active from inactivation by the digestive process in the GI tract (see also “Release Triggers for Emulsions”). However, osmotic pressures in the GI tract are often not controlled and this might limit the use of duplex emulsions. General Applications of W/O/W Emulsions The potential applications of double emulsion technology are enormous, with primary focus being in the food, cosmetics, medical and pharmaceutical industries. Potential applications have been demonstrated in improved biological availability (Elson et al., 1970; Brodin et al., 1978), delivery of drugs (Pandit et al., 1987), and adsorption of toxic compounds (Lata et al., 1987). Garti (1997b) reviewed the progress made up until then with respect to food applications of double emulsions. Since then many potential applications for double emulsions have been well documented and some have been patented (ThillFrancis, 1993; Gaonkar, 1994; Takahashi et al., 1994). In most cases double emulsions are aimed for slow and sustained release or controlled release of active matter from an internal reservoir into the continuous phase. Double emulsions have also been used to improve dissolution and solubilization of insoluble materials. Application of double emulsions in the protection of sensitive and active molecules from oxidation (Gallarate et al., 1999; Kim and Lee, 1999; Yoshida et al., 1999; Edris and Bergnståhl, 2001) has also been investigated, and double emulsions used to mask acid taste was described by Malone et al. (2003) (see below). Control of Taste Using W/O/W Emulsions It has already been mentioned in “Effect of O/W Emulsions on Taste Release and Perception” that the results by Malone et al. (2003) on the effect of oil content on taste perception indicated that the perceived intensity of a tastant is dependent on the oil-phase volume oil so for any given system the taste intensity can be manipulated by making w1/o/w2 duplex emulsions to control the apparent oil. Upon consumption the external w2 phase will be perceived but the internal w1 phase will be shielded from the taste receptors during the time scales of eating.


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In order to test this hypothesis, a series of w1/o/w2 double emulsions were made having fixed oil contents of 30% w/w and internal w1 phase volumes ranging from 0 to 50% w/w. The concentration of the solutes, in particular the citric acid, was at the same levels in both the w1 and w2 phases in order to remove the osmotic and concentration gradients that normally destabilize the emulsions during storage and to maintain the acid functionality in both phases. Their results showed that as more aqueous phase was incorporated into the oil phase the titratable acidity decreased (Malone et al., 2003). The acid in the internal w1 phase was not released from the duplex emulsion over the duration of the experiment (which had typical timescales in minutes). Sensory evaluation showed that the perceived acidity decreased, clearly demonstrating the dependence of taste perception on the volume of aqueous phase coming into direct contact with the mouth (i.e., w2). These results demonstrated that it is possible to manipulate the taste intensity by controlling the external w2 phase volume that contacts the taste receptors without resorting to traditional encapsulation approaches. This approach is different in that it provides a means of controlling active release whilst allowing for the thermodynamic stable distribution of the active between the constituent phases of the product. In emulsion-based foods, duplex emulsions also provide the benefit of controlled taste whilst remaining within acceptable textural limits for the product concerned.

Delivery of Hydrophobic Food Actives via O/W Emulsions Lipophilic Health Ingredients in O/W Emulsions Oil-in-water emulsions can be utilized to provide consumers with lipophilic health ingredients, such as dietary fat, antioxidants (such as the arytenoids -carotene and lycopene), vitamins (e.g. vitamin E), or sterols. They dissolve in the oil of the o/w emulsion, which may stabilize them during storage and increase their bioavailability. The use of dietary fat and how to protect these against oxidation are discussed in more detail in “Delivery of Dietary Fats as O/W Emulsions and Their Protection against Oxidation.” This later section may also illustrate routes to stabilize lipophilic health ingredients against oxidation (if necessary). Lycopene may have various health benefits, such as antioxidation, induction of cell communication and growth control, and lower risk of cancer (Ribeiro et al., 2003 and references therein). Ribeiro et al. (2003) found that the chemical stability of lycopene was particularly high in orange juice (pH 3.7), in contrast to skimmed milk (pH 6.6) or emulsions in water (pH 5.7). The authors stated that this result might be due to the antioxidant in the orange juice (ascorbic acid, or vitamin C), presence of iron in the milk, or influence of pH on oxidation. The use of -tocopherol or of nitrogen strongly inhibited the oxidation in all the three different food systems studied. The use of different emulsifiers (Tween 20, Lamegin ZE609, or lecithin) had little influence on the stability of lycopene. The bioavailability of lycopene dissolved in oil is high, in contrast to its crystal form (Ribeiro et al., 2003 and references therein). Therefore, o/w lycopene emulsions could be a base to develop functional foods. Plant sterols or phytosterols can reduce serum cholesterol by inhibiting intestinal cholesterol absorption (Trautwein et al., 2003). Different mechanisms—such as competing with cholesterol for absorption into the dietary micelles (the vehicles for the transport of lipophilic compounds in the intestine) or for cholesterol transporters, co-crystallization

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with cholesterol to form insoluble crystals and interference with the hydrolysis process by lipases and cholesterol esterases—are believed to play a role in this process. About 3 g/day of phytosterols are needed to have a significant effect on cholesterol lowering in the serum. The phytosterols are insoluble in water and poorly soluble in oil. Engel and Schubert (2005) produced a high loading of phytosterols in emulsions by using triglyceride and the emulsifiers lecithin or monoglyceride as crystallization inhibitors. Esterifying phytosterols with fatty acids increases their solubility in oil dramatically and this allows easy incorporation of plant sterol fatty acid esters into food products (both in fat-based products, such as margarine and spreads, and in o/w emulsion-based products, such as yoghurt or milk (Trautwein et al., 2003; Noakes et al., 2005 and references therein).

Aroma Release from O/W Emulsions The concentration of flavor (aroma) reaching the olfactory receptors will be influenced by the structure and composition of the food and by the physiological environment and mastication behavior that impacts on the rate of aroma released from the foodstuff (Harrison and Hills, 1997a, 1997b; Harrison, 1998; Malone et al., 2000, 2003). Specifically, the flavorrelease kinetics may depend on the flavor concentration, the microstructure and temperature of the food, the occurrence of reversible/irreversible binding, structure breakdown during mastication, mixing with saliva, and most importantly (for lipophilic flavors) the concentration of the fat (Delahunty and Piggott, 1995; Overbosch et al., 1991; Malone et al., 2000, 2003; Le Guen and Vreeker, 2003). Fat is recognised as playing a critical role in influencing many flavor attributes such as flavor quality, flavor release, flavor stability and the masking of off-flavor (McGorrin and Leland, 1994). Previous studies have demonstrated that when the fat content of a product is reduced the release of lipophilic flavors is altered resulting in changes to the intensity and release profiles, which alter the overall flavor balance and acceptability of the product (Overbosch et al., 1991; McGorrin and Leland, 1994; Malone et al., 2000; Doyen et al., 2001). These changes are particularly apparent when the fat content is reduced to below 5%, where both the intensity and temporal profile are significantly altered (Malone et al., 2000). These differences arise primarily due to the reduction in absorption of the lipophilic flavors in accordance with simple partition theory. Among all food constituents, lipids (and thus also emulsions) affect aroma release most notably, as they not only lower the aroma partial pressure or the air-product partition coefficient of most of the flavor compounds but also change the time scale of release with varying concentrations (de Roos, 1997; Guichard, 2002; Rabe et al., 2003; McClements, 2005). The higher the lipid content and the lipophilicity of the components (i.e., oil–water partition coefficient, Pow), the stronger the decrease in aroma release (with the exception of highly polar compounds possessing log Pow values 0, such as vanillin or acetic acid, see Leland, 1997). However, this effect is stronger under static conditions than under in vivo and artificial throat conditions (Weel et al., 2004b). Generally, increasing fat concentrations result in decreasing flavor release. The affinity of aroma to a lipid phase depends on its chemical composition, degree of saturation, chain length and sequence of fatty acids incorporated in a triacylglycerol. Hydrophobicity of the aroma compound is the determining factor for the distribution of aroma in the oil and water phases. Using homologues series of hydrocarbons, aldehydes, ketones and alcohols, Jo and Ahn (1999) found that aroma release decreased linearly with the fat content of the emulsion. The effect was less


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pronounced for ketones and greater for hydrocarbons, which can be explained by their different solubilities in oil. However, hydrogen bonds between aroma and lipids are an additional parameter (as has been demonstrated for, e.g., 1-octen-3-ol and linoleic acid by Le Thanh et al., 1998). Small changes in oil content can have significant effect on the aroma partial pressure or the air-product partition coefficient of lipophilic aroma compounds, in contrast to hydrophilic ones (Guichard, 2002). As a consequence, the overall aroma perception is changed often contributing to an imbalance to the nature of the overall flavor. Studies of the influence of the nature and surface area of an oil–water interface on the volatility of aroma in biphasic systems show that there is no general rule for understanding the effects of interfaces on the aroma release (Druaux and Voilley, 1997, and references therein). If the volatile compounds (such as dimethylsulfide) accumulate at the interface, the aroma concentration in the headspace of an emulsified system is significantly reduced compared to a two-phase, nonemulsified system. In the case of sunflower-oil/water emulsions that were stabilized with a sugar ester as the emulsifier, diacetyl displayed a higher volatility in w/o emulsions than in o/w emulsions. The presence of proteins at the oil–water interface of emulsions may induce retention for the compounds with high binding constants (Guichard, 2002). For example, ethyl hexanoate was significantly better released from emulsions containing -lactalbumin (protein with lower affinity for aroma compounds) than from those with -lactoglobulin. The presence of -lactoglobulin at the oil–water interface increases the resistance to the transfer of hydrophobic aroma compounds from oil to water and thus induces a decrease in aroma release (and perception). On the other hand, emulsifier concentrations above the cmc of Tween-80 did not influence the release (Rabe et al., 2003). The results with ionic emulsifiers might be different, due to ionic interactions. In general, droplet size of emulsions normally found in foods (5–100 m) will not affect the aroma release of a food product (Rabe et al., 2003; Weel et al., 2004b; McClements, 2005), although divergent results have been reported in the literature about the effect on droplet size on aroma release in vivo (Guichard, 2002; Rabe et al., 2003; Weel et al., 2004a). Smaller droplets may lead to faster mass transfer due to increased interfacial area and shorter diffusion distance through the oil droplets. However, the exchange of aromas between the two phases is generally assumed to be extremely rapid and it is the water–air interface that is the rate-limiting step for soft solids containing emulsion droplets in the normal size range (1–100 m). Moreover, recent data showed that only small amounts of volatiles are dynamically released from water within 30 s. Therefore, the re-equilibration process between the lipid and the aqueous phase should not be rate-limiting for the initial release process, as the concentration gradients to be adjusted are very flat. Surveys of food preferences among consumers indicate that the most important attributes of foods are aroma (flavor), appearance, and taste with flavor being the primary basis upon which food is selected and reselected. One aspect of flavor delivery that has had little attention is the control of the temporal flavor release profile (i.e., shape of the flavor delivery curve). An increasingly important market requirement is that a new flavor for a particular product should make a specific perceptual impression, for example a powerful initial impact or a novel sensation during eating. Since the rate and duration at which a flavor is delivered influence the perception, there is a rational that by controlling the temporal release profile the perception of that flavor can be manipulated. Factors that are important for flavor delivery in the mouth include the composition and microstructure of the product, dilution and mixing with saliva, changes in temperature, flavor concentration and the

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occurrence of reversible/irreversible flavor binding (Overbosch et al., 1991; de Roos and Wolswinkel, 1994; Taylor, 1996; see also “Release Triggers for Emulsions”). Furthermore, mass transfer of flavor in the mouth is affected by the gas and saliva flow rates, the degree of agitation and the temperature—all affected by the food structure and composition (Overbosch et al., 1991; Harrison and Hills, 1997a; Harrison, 1998; van Ruth et al., 2000). Aroma release in the mouth is a nonequilibrium process. Consequently, the maximum headspace concentration of a static system will hardly be reached in the mouth. A number of mathematical and mechanistic physicochemical models have been developed that describe flavor release from solid and semi-solid food matrices during eating (de Roos and Wolswinkel, 1994; Hills and Harrison, 1995; Harrison and Hills, 1996; Harrison et al., 1998; Wright et al., 2003, Wright and Hills, 2003). These theories have been based on the fact that during mastication, the kinetics of flavor release is primarily dependent on the generation of new surfaces (Harrison, 2000) and that the rate-limiting step is the mass transfer of flavor volatiles across the solid–saliva and saliva–gas interfaces for solid (Hills and Harrison, 1995; Harrison and Hills, 1996; Harrison et al., 1998; Wright and Hills, 2003; Wright et al., 2003) and semi-solid foods (Harrison et al., 1997b; Bakker et al., 1998). Much of the impetus for this work has been to model the link between the perception of flavor intensity and the foods composition, microstructure and breakdown during eating (Wright and Hills, 2003; Wright et al., 2003). Two important factors for controlling flavor delivery have been identified. These are (i) the rate-limiting step for soft-solid materials is the mass transfer of volatiles across the solid–liquid and liquid–gas interfaces (Harrison et al., 1998) and (ii) these rates are proportional to the mass transfer coefficient and the interfacial surface area (Hills and Harrison, 1995). This implies that by controlling the interfacial surface area by creating new surfaces (through particle breakdown) the temporal flavor profile could be altered. Harrison and Hills developed a mathematical model for the release of flavor volatiles from solid foods based on the two-film stagnant film theory (Hills and Harrison, 1995; Harrison and Hills, 1997a; Harrison et. al., 1998). This took into account the saliva flow, decrease in particle size, increase in new surfaces (surface area) and mixing with saliva during mastication. The expression they used based on Euler’s approximation was ⎡ c (t ) ⎤

M = hD Asf ⎢ cf − s ⎥ t Ksf ⎥⎦ ⎢⎣ where M is the total mass of volatile diffusing across the interface, hD is the mass transfer coefficient of a volatile, Asf is the surface area of the saliva–food interface, Ksf is the saliva–food partition coefficient, and cf and cs denote the concentration of flavor in the food and saliva, respectively. In principle, the same physicochemical model could be used to model the flavor released from particles that break down, provided that the model takes into account the different release mechanisms that are involved, each of which is rate determining at a different time. Based on considerations of mass transport between the food surface, the surrounding saliva layer and the gas phase of the breath, these treatments have drawn attention to the importance of describing the changing food surface area and saliva content during the course of mastication. One of the biggest challenges and as yet not really solvable with current model constraints is developing models that can predict the flavor-release behavior when the kinetics


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and mechanism of food structure breakdown are changing and sometimes in dramatic ways. Currently, most models are empirical and generally based on a number of assumptions that have not been fully tested. For example, these models have so far needed to assume idealized spherical shapes for the food particles, which can be related to surface area measurements. The goal would be to mathematically predict the effect of food structure and composition, material behavior and breakdown during eating on the time-intensity flavor release profile, based on mathematical models requiring fewer approximations. The increasing demand for low calorie foods has engendered much interest in the development of low-fat and sugar-free foods with the required consumer satisfaction. The difficulty in reduced-fat food lies in the multiple functions that fat plays, as it influences all aspects of food perception including appearance, texture, mouthfeel, and flavor. Fat is a source of flavor and also influences flavor character, flavor release, off-flavor, and taste perception. Lowering of fat levels is known to reduce the binding of lipophilic flavors to the food matrix thereby influencing the flavor balance (Overbosch et al., 1991; Shamil et al., 1991; Hatchwell, 1996; Malone et al., 2000; Doyen et al., 2001). Reduction in fat levels not only affects the intensity of the flavor perception but also influences the temporal profile. In high-fat products the initial impact of the flavor is gradual providing a well-balanced flavor profile whereas, in fat-free foods the flavor tends to be intense and transient manifesting itself as an “unbalanced” flavor with an “uneven” release profile.

Structured Emulsions in Hydrogels for Controlled Release of Aromas The microstructure and composition of food affects flavor release since aroma compounds may be adsorbed and absorbed by food components (Kinsella, 1990; Bakker, 1995) or influenced by the material and rheological properties of the food, which affect its breakdown during eating (Baines and Morris, 1987; Malkki et al., 1990; Guinard and Marty, 1995; Wilson and Brown, 1997). The relative importance of each of these mechanisms varies with the properties of the aroma compounds and the physicochemical properties of the food. Binding phenomena, however, generally involve interactions that are specific to the flavor and composition of the food and are not a versatile or practical means of controlling flavor release in low-fat foods. Likewise, the rheological and material properties have been demonstrated to influence flavor release but large textural changes are required in order to have a noticeable effect; in addition, the scale of these changes is beyond the textural tolerances that would be acceptable for many products. From the consideration of the partitioning of the flavor between the oil and aqueous phases at equilibrium, it can be shown that a considerable proportion of lipophilic flavors are present in the oil phase, even at relatively low oil phase volumes (0.5–5%). Hence, one strategy to control the release of lipophilic flavors would be to inhibit the rate of mass transfer of flavor molecules between the oil phase and the continuous aqueous phase. To do this a new approach was taken in our laboratory in which oil was encapsulated within gel particles (Malone and Appelqvist, 2003). In standard o/w emulsions, the rate of inter-phase transport of small solutes from the oil to the water phase occurs on a millisecond timescale (Wedzicha and Couet, 1995). Therefore, during eating, it would appear that the aqueous phase of low-fat o/w emulsions is rapidly stripped of its flavor, creating a strong driving force for rapid mass transfer of aroma from the oil phase to the aqueous phase. This rapid replenishment of the aqueous phase is the principal reason for the increase in maximum flavor intensity (FImax) and the rate of

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release into the headspace. One of the challenges in developing low-fat products is the design of microstructures that will reduce the rate of release of lipophilic aroma. Malone and co-workers (Malone et al., 2003) have demonstrated that one approach to reducing aroma release in low-fat systems is via incorporating the oil droplets into biopolymer gel particles, termed microstructured emulsions. In such microstructures the oil droplets are enveloped in a gel phase, creating a static diffusion layer around the oil droplets. This increases the path-length through which the aroma must diffuse before coming under the influence of the advective conditions existing within the bulk of the product during eating. The result of these structures was to inhibit the rate at which the lipophilic aromas replenish the continuous phase and reduce the rate of aroma release into the headspace. The principle behind encapsulating oil within a gelled particle was to increase the effective path-length for diffusion into the aqueous continuous environment to reduce the rate of lipophilic flavor release. A model for describing the flavor release from gel particles was developed by Lian et al. (2004). The model relates release rates to the composition (oil/water phase volume) and particle size and takes into account the resistance to mass transfer in both the particle and the bulk liquid phase. It should be noted that this approach differs from conventional encapsulation techniques in that it is the oil and not the aroma that is encapsulated. The aroma is allowed to reach thermodynamic equilibrium in the product, and it is the concentration of lipophilic aroma in the oil phase of the gel particles that forms the basis on which the controlled release is achieved. This is an important distinction because this approach does not attempt to resist the thermodynamic distribution of aroma between the oil and water phases. Release can be triggered by matrix melting in the mouth (e.g. gelatin), enzymatic breakdown (amylase hydrolysis of starch) and compression-induced fracture (chewing). Aroma release can take place upon breaking the initial equilibrium of aroma between the oil and water phases. As aroma is stripped from the aqueous phase the system attempts to reestablish the o/w equilibrium by diffusion of aroma from the oil but the additional diffusional pathway formed by the surrounding gel increases the half-life (t1/2), which, for diffusion into an infinite sink, can be approximated by

t1/2 =

(

0 . 693r 2 1 + Kow φo D

)

2

where r is the radius of the particle, Kow is the oil–water partition coefficient of the flavor compounds, o is the phase volume of oil in the particle, and D is the diffusion coefficient of the aroma compounds in the particle. From this equation, the key parameters that influence the rate of aroma release are the radius r, the oil content of the particle, and Kow of the aroma species. It has been possible to make microstructured emulsions from a range of biopolymer gels including Ca-alginate, gellan, gelatin, gelatin/gum arabic, agar, and starch. This provides the option to design particles that demonstrate controlled breakdown under physiological conditions during eating (Malone et al., 2003). Hence, by careful selection and design of the gel particle it should be possible to manipulate the shape of the aroma-release profile by the particle breakdown pattern. Other mechanisms that might contribute to changes in flavor-release profiles include brittle/elastic fracture involving syneresis of gel particles. For highly structured foods such


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as crackers, flavor release can be triggered by plasticization of the matrix by saliva. Changes in pH, ionic strength, and salt type (Kuhn and Foegeding, 1991) within the mouth environment could also be used to trigger physical disruption of particles to release flavor molecules in a controlled manner. There are a large number of factors such as biopolymer type, concentration, salt and so on that could be adjusted to design structured particles that break down and release under physiological conditions. By doing this, it is possible to manipulate the flavor release patterns, so that novel flavor profiles are obtained that may be appealing to the consumer. The ability to predict the effect of varying composition and structure on flavor-release profiles will be of great value to the food industry, particularly when trying to design new sensations. Combining microstructure design and mathematical modeling, it would be possible to formulate foods for a desired flavor profile, taking into account both the composition of food and individual or group differences in mastication behavior.

Delivery of Dietary Fats as O/W Emulsions and Their Protection against Oxidation Dietary fats fall in three main groups: saturated, mono-unsaturated and polyunsaturated. Olive oil is the best-known example of dietary oil that contains predominantly mono-unsaturated fatty acids. Polyunsaturated fatty acids are further divided into two subgroups called ω-6 and ω-3 fatty acids. Here, the term ω-6 means that the first double bond in the carbon backbone of the fatty acid occurs in the sixth carbon–carbon bond (counted from the terminal carbon atom opposite the acid group). Similarly, ω-3 fatty acids have their first double bond in the third carbon–carbon bond. Examples of ω-3 fatty acids are -linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is an essential fatty acid (i.e., it is not synthesized in the human body and must be obtained from food) and can be found in vegetable sources such as the seeds of flax or wall nut; EPA and DHA are abundantly present in fish oils and other marine oils and are assumed to play an important role in the prevention of cardiovascular diseases and several other disorders (Nestel, 2000). Furthermore, DHA has been proposed to play an important role in neural and visual developments of infants (Conner, 2000). Because of their beneficial health properties, ω-3 fatty acids have great potential as functional food ingredient (Jacobsen, 2004). Unfortunately, the use of ω-3 fatty acids in foods is limited due to their susceptibility to oxidation. Oxidation is a major cause of quality deterioration in foods containing significant amounts of ω-3 fatty acids and gives rise to changes in, for example, flavor (rancidity) and nutritional value. Considerable effort has been made to elucidate the mechanisms of lipid oxidation in bulk oils and emulsions. Lipid oxidation can occur via three mechanisms: autoxidation, photo-oxidation, or enzyme action. Emulsified foods usually do not contain enzymes that catalyze oxidation and therefore the latter mechanism is probably less relevant. Photo-oxidation occurs in the presence of light (visible or ultraviolet) and photosensitizing pigments (such as chlorophyll or riboflavin). Photo-oxidation can be a major cause of quality deterioration and is efficiently controlled by storing foods in the dark. Autoxidation is perhaps the most common mechanism in foods. It proceeds via a complex series of free-radical reactions with initiation, propagation, and termination steps (Karel, 1992). Transition metal ions (such as iron or copper) are known to be important catalysts for autoxidation. In theory, these metals are capable of directly breaking down unsaturated lipids (RH) into radicals. This reaction, however, is not believed to be important in initiating lipid oxidation. More likely, oxidation is initiated by

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metal-catalyzed decomposition of hydroperoxides (ROOH) (lipid hydroperoxides are found in small quantities in all food oils). For the initiation reaction, it is necessary that metal ions and hydroperoxides are in close proximity. In emulsion systems, hydroperoxides tend to accumulate at the surface of the oil droplets because of their relatively polar nature (McClements and Decker, 2000) and therefore are able to interact with metal ions or other pro-oxidants in the aqueous phase. This interaction leads to decomposition of the hydroperoxides and formation of highly reactive peroxyl (ROO•) or alkoxyl (RO•) radicals. Once these free radicals have been formed at the droplet surface they will interact with polyunsaturated lipids in their vicinity. This triggers a complex series of oxidation reactions (the reader is referred to Karel, 1992, for more details). Flavor changes typical for oxidized oil products (rancidity, fishy off-flavors, etc.) result from the formation of secondary oxidation products (such as aldehydes, ketones, alkanes, etc.) (Belitz et al., 2001). Various approaches can be taken to retard lipid autoxidation in food products. Removal of oxygen by packing under vacuum or nitrogen can be effective in certain cases. The use of high quality oils with low levels of hydroperoxides and ingredients with low levels of metalion contamination is also important. A well-known strategy of controlling lipid oxidation is by the addition of antioxidants (Frankel, 1996; McClements and Decker, 2000). Antioxidants are classified depending on their mechanism of action as either primary or secondary antioxidants. Primary antioxidants are compounds that react with free radicals and which are capable of interrupting lipid oxidation chain reactions. Tocopherols and plant polyphenols are important examples of natural primary antioxidants. Secondary antioxidants can retard lipid oxidation through a number of different mechanisms such as metal chelation, oxygen scavenging, or by replenishing hydrogen to primary antioxidants. Examples of metal chelators are ethylenediaminetetraacetic acid (EDTA) and citric acid; various food proteins and polysaccharides are also known for their excellent metal-chelating properties. Recently, the impact of microstructure and interfacial characteristics on the oxidative stability of emulsions has been highlighted (see McClements and Decker, 2000, for an excellent review). Various studies have shown that controlling the type and concentration of emulsifiers at the droplet interface can influence the rate of oxidation. One of the physicochemical factors that appear to be important is the electrical charge of the interfacial layer. An electrically charged surface will attract oppositely charged ions (counter ions) in the surrounding aqueous phase. A negatively charged surface (anionic emulsifier) will thus attract positively charged metal ions and bring them into close proximity of the lipid substrate. This is expected to reduce the oxidative stability of the emulsion. On the other hand, a positively charged emulsifier will repel metal ions from the surface and may thus help to stabilize the emulsion against oxidation. The importance of surface charge was demonstrated by Mei et al. (1997) for corn oil-in-water emulsions produced using three different emulsifiers. Oxidation rates (in the initial stage of the process) were found to be largest for an emulsion stabilized by sodium dodecyl sulfate (a negatively charged emulsifier); emulsions stabilized by Brij 35 (uncharged) or dodecyltrimethylammonium bromide (positively charged) appeared to oxidize at a lower rate (at pH 6.5). The authors suggested that the use of positively charged emulsifiers could be an effective means of retarding iron-catalyzed lipid oxidation. As low molecular weight cationic emulsifiers are not commonly used in foods, it was suggested to use protein stabilized emulsions at a pH below the isoelectric point (pI) of the protein. Under these conditions proteins can form a positively charged interfacial membrane around the oil droplet that will repel metal ions. Most food proteins have isoelectric points in the pH range 4.5–5.5 and thus positively charged emulsion


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droplets can only be prepared at relatively low pH (i.e., lower than usually desirable in food emulsions). Gelatin (produced by acid hydrolysis of collagen) is an exception as this protein has a relatively high isoelectric point (pI 7–8). Acid-treated gelatin can thus be used to prepare o/w emulsions with positively charged droplets over a wider range of pH values than is possible with other food proteins (Surh et al., 2006). The ability of positively charged proteins to retard lipid oxidation was studied by Hu et al. (2003a). The authors studied the oxidative stability of salmon oil-in-water emulsions stabilized by different whey proteins (viz. -lactalbumin, -lactoglobulin, sweet whey, and whey protein isolate). Oxidative stability was greatest at pH values below the isoelectric point of the proteins, which was explained from electrostatic repulsion of metal ions away from the positively charged emulsion droplet surface. The authors noted, however, that the ability of whey proteins to alter oxidation rates is not solely due to charge effects, because the positive charge ( potential) of the emulsion droplets (at pH 3.0) decreased in the order -lactoglobulin > -lactalbumin > whey protein isolate > sweet whey, whereas the oxidative stability decreased in the order -lactoglobulin sweet whey > -lactalbumin whey protein isolate. This suggests that other factors also influence the ability of adsorbed proteins to retard lipid oxidation. In a subsequent study the authors compared oxidation rates of corn oil-in-water emulsions stabilized by casein, whey protein isolate, and soy protein isolate (Hu et al., 2003b). The oxidative stability (at pH 3.0) decreased in the order casein > whey protein isolates soy protein isolate. It was concluded that the magnitude of the positive droplet charge again is not the only factor responsible for differences in oxidative stability and that other membrane properties probably also play a role. One of the factors that might be involved is the thickness of the interfacial membrane: a thick layer at the emulsion droplet interface is assumed to hinder interactions (i.e., acts as a physical barrier) between water-soluble pro-oxidants and lipids inside the emulsion droplets (Silvestre et al., 2000). Caseins form a relatively thick layer on the emulsion droplet interface (as compared to, e.g., whey protein isolate), which might contribute to the lower oxidation rate observed in casein-stabilized emulsions. Another factor of importance is the metal–ion chelation properties of proteins. Villiere et al. (2005) compared the oxidative stability of sunflower oil-in-water emulsions stabilized by bovine serum albumin and sodium caseinate. At pH 6.5, emulsions stabilized by sodium caseinate were found to oxidize faster than emulsions stabilized by bovine serum albumin. The faster oxidation was attributed to the better chelating properties of sodium caseinate (as compared to bovine serum albumin) and to electrostatic interactions that favor positioning of metal ions at the interface. The authors suggest that proteins with good metal chelation properties, such as sodium caseinate, should not be used as emulsifiers in systems containing oxidation sensitive lipids, but preferably should be added to the aqueous phase as a natural antioxidant after the emulsification process. This does not hold for emulsions in which metal ions are deactivated and kept away from the interface by the addition of EDTA; in the presence of EDTA, emulsions stabilized by sodium caseinate appeared to be more stable than emulsions stabilized by bovine serum albumin, which was attributed to free-radical-scavenging properties of sodium caseinate. In protein-stabilized emulsions, usually only a fraction of the proteins adsorbs at the oil droplet interface, whereas the remaining proteins are located in the continuous water phase. If the proteins in the water phase are able to chelate metals ions, they can remove the ions away from the oil droplet and inhibit oxidation. The impact of various continuous phase proteins (viz., soy protein isolate, casein and whey protein isolate) on the oxidative stability

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of menhaden oil-in-water emulsions was studied by Faraji et al. (2004). In their experiments, continuous phase proteins were removed in a number of “washing” steps and the oxidative stability of washed emulsions was compared to those of nonwashed emulsions. Unwashed emulsions (at pH 7.0) were more oxidatively stable than washed emulsions indicating that continuous phase proteins are indeed antioxidative and could be used as an effective means of protecting ω-3 fatty acids. Under the conditions used, soy protein isolate was found to have the greatest antioxidant activity of all proteins tested, that is, larger than casein, which was found to have the largest chelation capacity. The authors suggested that in case of soy, antioxidant activity most likely results from a combination of metal-ion chelation and free-radical scavenging. The latter may be due to the presence of specific amino acids with antioxidant activity (such as free sulfhydryl groups) or antioxidants (e.g., isoflavones) associated with the soy protein. Klinkesorn et al. (2005) studied the effect of multilayer membranes on the oxidative stability of tuna oil-in-water emulsions. Multilayer membranes were produced by sequential deposition of oppositely charged emulsifiers. First, an emulsion was made by dispersing oil in a solution of an anionic emulsifier (lecithin) and then this emulsion was mixed with a solution of a positively charged polysaccharide (chitosan). This “layer-by-layer deposition technique” could be used to produce cationic and relatively thick emulsion droplet interfaces. The oxidative stability of emulsion droplets coated by a lecithin-chitosan multilayer was found to be higher than that of emulsion droplets coated with lecithin only. The improved stability is likely due to the cationic nature of the droplets that causes repulsion of the prooxidative metals and possibly also from a thicker interfacial region that reduces interactions between lipids and water-soluble prooxidants. According to the authors, production of emulsion droplets with a multilayer lecithin-chitosan coating might be an excellent technology for protecting labile oils. The previous examples have highlighted the importance of prooxidant location. However, the location of chain-breaking antioxidants can also play a critical role in stabilizing emulsions (Frankel, 1996; McClements and Decker, 2000; Chaiyasit et al., 2005). Chainbreaking antioxidants are expected to be most effective at retarding lipid oxidation when they are located in the oil–water interfacial region, where oxidation reactions are initiated. Hydrophilic antioxidants, in general, are less effective than lipophilic antioxidants in o/w emulsions. This is because a significant portion of the hydrophilic antioxidant will partition into the aqueous phase, where it is considered to be inactive (Schwarz et al., 2000). The effectiveness of chain-breaking antioxidants in general increases as their polarity decreases, because they are then more likely to be localized in the lipid phase or near the lipid surface (Huang et al., 1996a, 1996b, 1997). The importance of the electrical charge of chain-breaking antioxidants (relative to the charge of emulsion droplets) was demonstrated by Mei et al. (1997). The authors measured oxidation rates for salmon oil-in-water emulsions stabilized by anionic surfactants (sodium dodecyl sulfate) or uncharged surfactants (Brij 35) containing negatively charged, uncharged, or positively charged phenolic antioxidants. In emulsions stabilized by sodium dodecyl sulfate (at pH 7), the negatively charged antioxidants were found to be less effective than the positively or uncharged antioxidants, which suggests that the negatively charged antioxidants are electrostatically repelled from the surface of the emulsion droplets. In emulsions stabilized by Brij 35, the uncharged phenolic antioxidants were found to be most effective, which was thought to result from the low solubility of uncharged phenolic antioxidants (as compared to the charged phenolics) and a tendency to


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accumulate at the oil–water interface. Physical properties, such as polarity and partitioning between different phases, are thus important criteria in selecting a proper antioxidant system. However, as mentioned by Huang et al. (1997), other criteria such as relative oxidative stability and hydrogen-donating ability in different phases should also be considered in the selection of antioxidants. The literature on oxidation in real food products (e.g., fish-oil enriched mayonnaise, margarine, or milk drinks) is still relatively limited (Jacobsen, 2004). Most studies so far have concentrated on model emulsion systems. The knowledge gained from model studies is expected to lead to new product opportunities. In particular, the possibility of designing interfacial properties (“interfacial engineering”) will enable food scientists to engineer foods with improved oxidative stability.

Future Trends Current efforts are focusing on naturalness, convenience, and perfection. The use of “natural emulsions” and the production of monodispersed emulsions are discussed here. The use of nanoemulsions will be discussed in Chapter 2 in this book.

Nature-Made Emulsions Nature-made emulsions can be used when purified or reconstituted. The idea here is to entrap active components in these pre-formed emulsions. Potentially all plant, animal, and microbial cells can be used and as with all release devices selection will be dependent on the ability of the system to deliver the required release characteristics against a particular application. Three types of preformed capsule systems will be briefly discussed here, oil or lipid bodies, yeast cells, and plant cells. Their use may enhance the “natural” image of a food product, in addition to other functional advantages. Oil or Lipid Bodies Seed oil bodies (Figure 3.3) are lipid storage organelles of 0.5–2 m in diameter and comprise a triacylglycerol matrix shielded by a monolayer of phospholipids and proteins. These proteins include abundant structural proteins, oleosins (a structural protein), and at least two minor proteins caleosin (a calcium-binding protein) and steroleosin (an NADP-dependent sterol-binding protein) (Chen et al., 2004). Native oil bodies—modified and reconstructed— can be a useful structure for a range of applications especially as a carrier for hydrophobic molecules. The layer of oleosin coating imparts stability to the oil body by protecting the phospholipid monolayer both from attack by the phosphorlipases present in the cell and by giving the oil body a negatively charged surface, which prevents the oil bodies from aggregating and stops coalescence if the structures touch (Tzen and Huang, 1992). In fact oil bodies are remarkably stable both in and out of the cell due to steric hindrance and electronegative repulsion provided by the oleosins on the surface of the oil bodies (Tzen et al., 1992). Oleosins are insoluble in aqueous media, have a pI of 5.7–6.6 and make up 8–20% of the total seed protein (Murphy, 1993; Huang, 1996). It is thought that the oil body size is determined by the ratio of oil to oleosin during oil body formation (Murphy, 1999), which means that it could be possible to control the size of

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(a)

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(b)

Figure 3.3. Confocal scanning light microscopic images of an intact pine tree seed cell (left) in the presence of Nile Blue. The dotted line represents the cell wall. Purified oil bodies could be isolated from these cells (right). The light grey spheres in both images depict the oil core of the oil bodies. The white colour represents the protein containing cell structures (hardly visible in the right picture). These pictures have been kindly provided by our colleagues C.M. Beindorff and E. Drost of Unilever R&D Vlaardingen, The Netherlands.

oil body by controlling the rate that oleosin is produced. The nature of the oil within the oil body can also be important both for determining the types of actives that can be encapsulated and for the specific application in foods and pharmaceuticals. During normal extraction of oil from plant materials the oil bodies are normally destroyed due to the high shear processes of crushing and milling followed by degumming and further refining (Gunstone et al., 1994). In the last ten years a number of companies (e.g., Sembiosys) have developed methods to extract oil bodies from seeds or plants without destroying them and in good yield. A number of papers and patents have been published concerning the specific use of oil bodies for therapeutic and nutraceutical purposes by attaching active peptides to the termini of the oleosin protein and using the oil body as a carrier of the active component concerned (Boothe et al., 1997; Deckers et al., 1998, 1999). This type of research has also stimulated many workers in the field to look at a number of ways in which oil bodies can be modified to make them more functional. This has included improving the payload of lipophilic material by extracting all of the oil from the oil body to leave an empty ghost (Tzen and Huang, 1992; Tzen et al., 1998), which can be later filled with a combination of different oils and actives. These regenerated oil bodies possess the same physiochemical properties as the original oil bodies but now possess higher payloads of active. Oil bodies have also been modified to target specific sites for the delivery of an active by modifying the oleosin proteins, which due to their high level of functional groups make them very susceptible to alterations. Much is already known about the genetics of different plant species, and genetically modified oil bodies have already been produced in which, for example, -glucuronidase enzyme has been fused to an oil body and shown to be active


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(Abenes et al., 1997). Other forms of modification to the oil bodies have been via chemical modification (cross-linked with glutaraldehyde or genipin) to enhance their stability (Peng et al., 2003) and self-assembling targeting systems, in which oil bodies can be targeted effectively to their site of action via multivalent antigen-binding proteins (Frenken et al., 1999) since antibodies are easily raised to oleosin (Cummins and Murphy, 1992; Wu et al., 1997). Since the constituents of native oil bodies and their proportions are well known, it has been possible to produce stable artificial oil bodies technically reconstituted from their three main components: triglycerols, phospholipids, and oleosin protein (Tzen and Huang, 1992; Tzen et al., 1998; Tai et al., 2002). Artificial oil bodies were successfully reconstituted with various compositions of these components and compared to native oil bodies for size and stability. Increasing the size of the oil body led to a decrease in the thermostability and structural stability of the reconstituted oil bodies. Native oil bodies, modified and reconstructed, can be a useful structure for a range of applications especially as a carrier for hydrophobic molecules such as flavors, vitamins, nutraceutical actives (e.g., antioxidants) and pharmaceutical drugs (e.g., steroids), and cosmetic lipids (e.g., healthy fatty acids) (Peng et al., 2003). Other applications are as a vehicle for the production of recombinant proteins (van Rooijen and Moloney, 1995), as a biocapsule for encapsulation of lactic acid bacteria in dairy products (Hou et al., 2003) and the use of artificial oil bodies reconstituted with olive oil and phospholipid in the presence of caleosin to elevate the bioavailability of hydrophobic drug cyclosporin A via oral administration (Chen et al., 2005). Yeast Cells Yeast cells have been explored recently by a number of workers for their potential as controlled delivery devices for flavor release (Bishop et al., 1998; Normand et al., 2005) and to improve the bioavailability of poorly soluble drugs in the GI tract (Nelson et al., 2006). Indeed, yeast cells have been investigated as early as the 1970s when Laboratoires Sérozym, France (Laboratoires Sérozym, 1973) and Swift and Co., USA (Shark, 1977) patented a technique using specially prepared yeast cells containing >40% loading of lipid. They described the encapsulation of dyes, drugs, and flavors in viable and nonviable microorganisms including fungi and protozoa. The mechanism of the encapsulation process in yeast cells relies on the relative affinity of would-be encapsulated material for the internal lipid phase of the yeast cell. Flavor components which display ideal solution with this lipid phase will be encapsulated to the greatest degree. It has been suggested that the internal lipid phase is primarily made of phospholipid bilayer membranes unlike a classic micelle structure. Actives which are extensively nonpolar (such as -carotene) might be expected to exist in the interior of the micelle (Wedzicha, 1988); however, their molecular size would involve geometric changes to the micelle and therefore very high molecular weight hydrocarbons may be excluded from the cell. Rebalancing flavors, the use of co-encapsulates to alter the properties of the internal lipid phase to compensate for disproportionate uptake, and other cell modifications such as extraction of the cell wall using detergents (Chow and Palecek, 2004) to improve permeability have helped extend the allocation range of the yeast cells as preformed capsules.

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Indeed, yeast cell wall composition and thickness can be modified using different cell strains for enzyme expression or by mutating genes involved in cell wall biosynthesis or degradation (Chow and Palecek, 2004). Under dry conditions (e.g., water activity below 0.7), release rates are considerably low due to limited mass transfer. Flavour release can be resumed upon rehydration (Normand et al., 2005). Normand et al. (2005) have used limonene as a model marker for hydrophobic flavors and discussed the flavor-release mechanism with regard to the cell wall structure and its behavior toward water uptake and also desorption during the drying of the yeast cells. The basis of the driving force for flavor release from hydrated yeast cells appears in good agreement with the theory describing monolithic solution release, a theory derived by Crank (1956) and applied to spherical controlled-release devices by Baker and Lonsdale (Baker and Lonsdale, 1974; Baker, 1987) demonstrating a biphasic release pattern. Importantly, the resistance to transfer of flavor materials within the hydrated yeast cell is not rate-determining, and the kinetics of release are dictated by the aqueous phase solubilities. Plant Cells A plant cell in nature is surrounded by a cell wall and therefore not prone to allowing macromolecules from outside to accumulate within the cell (Rosenbluh et al., 2004). Indeed, cells are protected from the surrounding environment by plasma membrane, which is impenetrable for most hydrophilic and hydrophobic materials. However, it would appear that a process resembling cell endocytosis, which occurs in animals, can also occur in plant cells (Robinson et al., 1998; Daelemans et al., 2002) although much less is known about the detailed mechanism. It has been shown that the addition of macromolecules that have been biotinylated such as hemoglobin, BSA or IgG to cultured soybean cells resulted in their intracellular accumulation (Horn et al., 1990, 1992) and that this process was temperature dependent indicating a requirement for metabolic energy. There are, however, certain low molecular weight proteins that appear able to cross the plasma membrane at least for mammalian cells without the involvement of the endocytic pathway (Lindgren et al., 2000) and have been termed “cell-penetrating protein/peptides” (CCP). These types of molecules such as purified core histones (Rosenbluh et al., 2004) are also capable of crossing plasma membranes of plant cells and acting as CCPs in plant cells. These molecules can be used to mediate the internalization of larger molecules such as oligonucleotides, peptides, proteins, and nanoparticles following their conjugation to the CCP (Fawell et al., 1994; Pooga et al., 1998; Astriab-Fisher et al., 2002). In plant cells it has been confirmed using confocal laser-scanning microscopy that histone-BSA conjugates have penetrated into protoplasts of petunia plants via direct translocation through the plasma membrane (Rosenbluh et al., 2004). This type of technology therefore gives an approach that could be used to introduce and deliver a whole range of actives and macromolecules into plant cells. Although in the biotechnology area, the internalization of CPPs and the attached molecules by plant cells may open up a new method for transfection in plant cells (Mae et al., 2005), this method could also be used to load plant cells with active molecules such as flavors, vitamins, and so on to be used as controlled delivery devices. Due to the plasma membrane and cell wall structures, plant cells make excellent preformed capsules that can contain a range of macromolecules in a very natural system, which can be used in a range of foods.


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Monodispersed Emulsions Several technologies have been developed to produce highly uniform emulsion droplets (see Link et al., 2004, and references therein). Technologies to reduce polydispersity of already formed emulsions include repeated fractionation and shearing immiscible fluids between uniformly separated plates (Mabille et al., 2003). Alternatively, single-drop technologies are available, such as flow through a micromachined comb, hydrodynamic flow focusing through a small orifice, and drop break off in co-flowing streams (Figure 3.4). Using microchannel technology, more-complex droplet structures have been prepared: w/o/w emulsions (Okushima et al., 2004; Sugiura et al., 2004), gelled beads with a variety of shapes (Seo et al., 2005; Dendukuri et al., 2006), Janus particles where the two halves present different properties (Nisisako et al., 2004), and a variety of encapsulates. Currently, these single-drop technologies are limited in production rate (in the order of l–ml per hour). Highly parallel production at a small scale by microfluidic technology may reduce this limitation in the future. Monodispersed emulsions may have a more defined behavior and release pattern of entrapped actives than polydispersed ones. This can be very important in pharmaceutics and when the emulsions are used as a template to make new materials for, for example, electronics. Currently, it is not clear whether or not this would constitute a real advantage in food systems. Using these technologies may allow forming a better picture of the rheological and organoleptic behavior of monodispersed emulsions by experimentally testing their properties.

Microchannel (100 μm width)

(a) Oil flow

Tip

Water flow Oil flow

(b)

Figure 3.4. Emulsion production via microfluidic technology. Here a so-called psi-junction is used. Other geometries are possible as well. (a) shows the schematic overview and (b) is a microscopic “real” picture that has been kindly provided by Conchi Pulido de Torres, Unilever R&D Colworth, UK.

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4 Applications of Probiotic Encapsulation in Dairy Products Ming-Ju Chen and Kun-Nan Chen

Introduction Most probiotics in the food supply are used in fermented milks and dairy products; in fact, dairy products are the major carriers of probiotics available today. Probiotics can be defined as living microbial supplements which can improve the balance of intestinal microorganisms (Fuller 1992). This definition was broadened by Havenaar and Huis in’t Veld (1992) to a “mono- or mixed-culture of live microorganisms which benefit man or animals by improving the properties of the indigenous microflora.” The probiotic effect has been attributed to the production of acid and/or bacteriocins, competition with pathogens and enhancement of the immune system. Claimed benefits include controlling serum cholesterol levels, preventing intestinal infection, improving lactose utilization in persons who are lactose intolerant, and possessing anticarcinogenic activity. Good probiotic viability and activity are considered essential for optimal functionality (Mattila-Sandholm et al. 2002; Champagne and Gardner 2005). Furthermore, the ability of microorganisms to survive and multiply in the host strongly influences their probiotic benefits. The bacteria in a product should remain metabolically stable and active, surviving passage through the upper digestive tract in large numbers sufficient enough to produce beneficial effects when in the host intestines (Gilliland 1989). Adequate numbers of viable cells, namely the “therapeutic minimum,” need to be regularly consumed in order to transfer the probiotic effect to consumers. Survival of these bacteria during the product shelf life until being consumed is therefore an important consideration. Suggested beneficial minimum level for probiotics in yogurt is 106 cfu/mL (Robinson 1987; Kurman and Rasic 1991) or the daily intake should be about 108 cfu/mL. Earlier studies indicated that some strains of probiotics, especially Bifidobacterium spp., lack the ability to survive gastrointestinal conditions (Berrada et al. 1991; Lankaputhra and Shah 1995). Other studies have also reported low viability of probiotics in dairy products such as yogurt and frozen dairy desserts (Iwana et al. 1993; Shah and Lankaputhra 1997; Schillinger 1999) due to the concentration of lactic acid and acetic acid (Samona and Robinson 1994), low pH (Martin and Chou 1992; Klaver et al. 1993), the presence of hydrogen peroxide (Lankaputhra and Shah 1996), and the oxygen content (Dave and Shah 1997). Methods for protecting probiotics including selection of acid-resistant strains, control of over-acidification of dairy products, and the addition of cysteine or an oxygen scavenger such as ascorbic acid (Dave and Shah 1997) have been proposed by various studies (Dave and Shah 1998; Adhikari et al. 2000; Krasaekoopt et al. 2003). Encapsulation has been investigated for improving the viability of microorganisms in both dairy products and the intestinal tract (Prevost and Divies 1988; Lacroix et al. 1990; Champagne et al. 1992). Encapsulation is a physicochemical or mechanical process in which particles containing active ingredients are covered by a layer of another material, providing protection and

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controlled release of the primary ingredients as well as making the ingredients more convenient to work with (Thies 1996). The selection of different types of coating materials usually depends on the functional properties of the microcapsules and the coating process used (Hegenbart 1993). For dairy and food applications, probiotic encapsulation in food grade, porous matrices has been most widely used (Champagne et al. 1994). Spherical entrapment beads are produced using spray-drying, extrusion, or emulsification techniques. The following sections describe the techniques, effects, and applications of probiotic encapsulation in dairy products. Published data on new techniques of probiotic encapsulation with survival of probiotic capsules in dairy products and in the intestines are also discussed.

Techniques for Probiotic Encapsulation Encapsulation of probiotics for use in dairy products or biomass production can be achieved in two ways: physicomechanically and chemically. The probiotics are encapsulated in the gas phase during physicomechanical procedures including spray-drying technique whereas, probiotic encapsulation is performed in liquid by thermal or ionotropic gelation of the droplets including extrusion and emulsion techniques. All three techniques have been proven to increase the survival of probiotics by up to 90% (Kebary et al. 1998).

Spray-Drying Technique Among the well-known microencapsulation methods, spray-drying is most widely used in the chemical, pharmaceutical, and food industries due to its inherent attributes such as high production rates and relatively low operational cost (Gibbs et al. 1999). The principle of spray-drying technique involves dissolving a polymer, in the continuous phase, which surrounds the core material particles (encapsulant such as probiotics) inside the sprayed droplets. The drying process causes this solution to shrink into a pure polymer envelope enclosing the core material. The resulting capsules are obtained as free-flowing dry powder. Table 4.1 shows probiotic encapsulation using the spray-drying technique in dairy products and biomass production. Various carrier matrices including starch (O’Riordan et al. 2001; Lian et al. 2003), gelatin (Lian et al. 2002, 2003), gum arabic (Lian et al. 2002, 2003), skim milk (Gardiner et al. 2002; Lian et al. 2003; Ananta et al. 2005), cellulose acetate phthalate (CAP; Favaro-Trindade and Grosso 2002), whey protein (Picot and Lacroix 2003, 2004), gum acacia (Desmond et al. 2002), and prebiotics (Ananta et al. 2005) have been reported and applied to various dairy products including yogurt (Picot and Lacroix 2004), dry dairy beverages (O’Riordan et al. 2001), and cheddar cheese (Gardiner et al. 2002). However, exposure to high air temperatures required to facilitate water evaporation during the passage of the bacteria in the spray-drying chamber exerts a negative impact on their viability and hampers their activity in the spray-dried product (Ananta et al. 2005). The survival of encapsulated microorganisms produced by spray-drying will be discussed in more detail in a later section.

Extrusion Technique Extrusion is the simplest and most common technique used to produce probiotic capsules with hydrocolloids (King 1995). The principle of this technique simply involves preparing a hydrocolloid solution, adding the probiotic ingredient to the solution and dripping the cell


Applications of Probiotic Encapsulation in Dairy Products

Table 4.1.

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Probiotic encapsulation by spray-drying in dairy products and biomass production

Probiotics

Carrier matrix (%)

Bifidobacterium PL1

10% starch

L. paracasei L. acidophilus

Inlet and outlet temperature

Application

Reference

Inlet: 60–140°C Outlet: 45°C

Dry beverage

O’Riordan et al. (2001)

20% reconstituted skim milk

Inlet: 175°C Outlet: 68°C

Cheddar cheese

Gardiner et al. (2002)

Cellulose acetate phthalate

Inlet: 130°C

B. lactis

Favaro-Trindade and Grosso (2002)

Outlet: 75°C

L. paracasei

Gum acacia

Inlet: 170°C Outlet: 95–105°C

Desmond et al. (2002)

B. longum

30% gelatin

Inlet: 100°C

Lian et al. (2002, 2003)

B. infantis

35% soluble starch 35% gum arabic 15% skim milk

Outlet: 50–60°C

B. breve

85% milk fat/5–15% whey protein

Inlet: 160°C

B. longum

10% whey protein

Outlet: 80°C

B. breve

85% milk fat/5–15% whey protein

Inlet: 160°C

B. longum L. rhamnosus GG

Picot and Lacroix (2003) Yogurt

Picot and Lacroix (2004)

Outlet: 80°C 20% skim milk/ oligofructose or polydextrose

Outlet: 70–100°C

Ananta et al. (2005)

suspension through a syringe needle or nozzle spray machine in the form of droplets which are allowed to free-fall into a hardening solution or setting bath. This extrusion technique produces large particles with uniform particle size. Table 4.2 shows probiotic encapsulation using extrusion techniques in dairy products and biomass production. The common polymer used to produce probiotic encapsulation matrix by extrusion technique is alginate (Krasaekoopt et al. 2003). Other food-grade encapsulation materials like gellan gum and xanthan gum (Sun and Griffiths 2000; McMaster et al. 2005) have also been proposed for encapsulating probiotics. Many dairy products including yogurt (Prevost and Divies 1987; Sun and Griffiths 2000; Krasaekoopt et al. 2004; Iyer and Kailasapathy 2005), cheese (Prevost and Divies 1988), and cream (Prevost and Divies 1992) carry encapsulated probiotics produced by extrusion. One of the major advantages of this method is that the viscosity of the fluid does not limit capsule generation (Prüße et al. 2000). Furthermore, the biological matter can be treated at lower temperatures.

Emulsion Technique The emulsion technique has successfully been used to encapsulate lactic acid bacteria in both batch (Lacroix et al. 1990) and continuous fermentation processes (Audet et al. 1992).

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86

L. acidophilus

L. casei B. bifidum L. bulgaricus B. lactis

L. acidophilus L. acidophilus L. casei B. bifidum L. acidophilus

B. longum B. infantis

Calcium chloride

0.5 M calcium chloride 0.1 M calcium chloride

0.05 M calcium chloride

2% sodium alginate

2% sodium alginate 0.75% gellan/1% xanthan gum Sodium alginate poly-L-lysine Chitosan

0.1–1.0 M calcium chloride 0.05 M calcium chloride


2% sodium alginate 0.1 M calcium chloride 0.1 M calcium chloride


2–4% sodium alginate 0.75% gellan/1% xanthan gum 0.75–2% sodium alginate 2% sodium alginate

0.05 M calcium chloride 0.1 M calcium chloride 1.0 M calcium chloride

1.5% sodium alginate 2% sodium alginate 0.6% sodium alginate 1.0 M barium chloride 2% sodium alginate

Lactococcus lactis ssp. cremoris B. bifidum


1.85% sodium alginate

L. delbrueckii ssp. bulgaricus Streptococcus thermophilus L. plantarum L. lactis L. casei

Hardening bath

Supporting material (%)

Probiotics

Raftiline®/Raftilose®

Hi-maize starch

Chitosan No

Sodium alginate poly-L-lysine chitosan

No Chitosan

Poly-L-lysine chitosan No No

Chitosan

No No Chitosan

No

Special treatment

Probiotic encapsulation by extrusion technique in dairy products and biomass production

Amasi (sour milk products) Yogurt

Yogurt

Yogurt

Biomass production

Biomass production Cream

Cheese

Aplication

Iyer and Kailasapathy (2005)

Lee et al. (2004) McMaster et al. (2005)

Krasaekoopt et al. (2004)

Chandramouli et al. 2004 Krasaekoopt et al. (2004)

Lee and Heo (2000) Sun and Griffiths (2000)

Cui et al. (2000)

Zhou et al. (1998)

Kearney et al. (1990) Prevost and Divies (1992) Yoo et al. (1996)

Prevost et al. (1987)

Reference

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Table 4.2.




87

The principle of these techniques is based on the relationship between the discontinuous and the continuous phases. A small volume of the cell-polymer suspension (i.e., the discontinuous phase) is added to a large volume of vegetable oil (i.e., the continuous phase). The mixture is then homogenized to form a water-in-oil emulsion. Once the water-in-oil emulsion is formed, the water-soluble polymer must be insolubilized to form tiny gel particles within the oil phase. The insolubilization method of choice depends on the type of supporting material used. The beads are harvested later by filtration. For encapsulation in an emulsion, an emulsifier and a surfactant are needed. Emulsifiers such as Tween 80 can break up water and oil emulsions as well as prevent spheres from coalescing before breaking up the emulsion. A surfactant such as sodium lauryl sulfate (SLS) is used to lower the surface tension in the coating matrix in order to reduce the size of the spheres. Table 4.3 shows probiotic encapsulation using emulsion technique for dairy products and biomass production. Various supporting materials have been used to encapsulate probiotics by the emulsion method including alginate (Sheu and Marshall 1993; Sultana et al. 2000; Truelstrup et al. 2002; Song et al. 2003; Shah and Ravla 2004), -carrageenan (Dinakar and Mistry 1994; Adhikari et al. 2000, 2003), CAP (Modler and Villa-Garcia 1993), chitosan, and gelatin (Peniche et al. 2003). This type of probiotic beads have been successfully applied to yogurt (Adhikari et al. 2000; Sultana et al. 2000; Adhikari et al. 2003), cheddar cheese (Dinakar and Mistry 1994), milk (Truelstrup et al. 2002), and ice cream (Sheu and Marshall 1993; Shah and Ravla 2004). This technique provides both encapsulated and entrapped core materials and is easy to scale up for large-scale production.

Advantages and Disadvantages of Various Probiotics Encapsulation Techniques A comparison of different encapsulation techniques is presented in Table 4.4. Both spraydrying and extrusion (Krasaekoopt et al. 2003) are relatively simple techniques. Conversely, the emulsion technique based on the relationship between the discontinuous and continuous phases is more complex. Although both spray-drying and emulsion techniques are easier to scale up, Picot and Lacroix (2003) used an emulsification/spray technology to produce microcapsules containing micronized skim milk powder dispersed in milk fat droplets surrounded by an insoluble whey protein film. This technique is claimed to be simple and can be easily scaled up for microencapsulation of dry probiotic cultures. Encapsulation of probiotics using natural biopolymers such as calcium alginate, -carrageenan, and gellan gum is currently applicable only on a laboratory scale (Doleyres and Lacroix 2005). The high viscosity of these coating materials appears to hamper the efficiency of encapsulation (Krasaekoopt et al. 2003). Scale-up production of encapsulated probiotics via extrusion is more difficult due to the slow formation of beads (Krasaekoopt et al. 2003). The sizes of beads formed from spray-drying and emulsion are smaller than those produced by the extrusion method. With the extrusion method, the size of the capsules is highly dependent on the viscosity of sodium alginate solution, the extruder orifice diameter, and the distance between the syringe and the calcium chloride collecting solution (Smidsrod and Skjak-Braek 1990). A higher concentration of sodium alginate results in significantly high viscosity which leads to large particle sizes. Spherical beads, prepared by extrusion, are approximately 2–3 mm in diameter, while those made by emulsification techniques have

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88 Vegetable oil Soy oil Vegetable oil Vegetable oil Vegetable oil

Corn salad oil Vegetable oil Sesame oil/vegetable oil Vegetable oil

2% -carrageenan 3% -carrageenan/ locust bean gum 2% -carrageenan 2% alginate 3% alginate

1% alginate 2% -carrageena Artificial oil 3% alginate

B. bifidum

B. longum

B. longum L. acidophilus Bifidobacterium spp. B. adolescentis B. breve B. lactis B. longum L. casei

B. longum L. bulgaricus L. acidophilus

Bifidobacterium spp.

Vegetable oil

Soy oil

Continuous phase

3% alginate

3% -carrageenan/ locust bean gum

Concentration of supporting material (%)

S. thermophilus Lc. lactis L. bulgaricus

L. bulgaricus

Probiotics

Microporous Glass Membrane No No No

No

No Hi-maize starch

No

No

No

No

Special treatment

Probiotic encapsulation by emulsion in dairy products and biomass production

Frozen dessert

Stirred yogurt

Milk

Set yogurt Yogurt

Cheddar

Ice milk

Biomass production

Application

Adhikari et al. (2003) Hou et al. (2003) Shah and Ravla (2004)

Song et al. (2003)

Truelstrup et al. (2002)

Adhikari et al. (2000) Sultana et al. (2000)

Sheu and Marshall (1993) Dinakar and Mistry (1994) Maitrot et al. (1997)

Audet et al.(1989)

Reference

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Table 4.3.




Table 4.4.

89

Advantages and disadvantages of encapsulation methods

Scale-up Encapsulating process Variety of coating materials Shape and size Survival of microorganisms

Spray-drying

Extrusion

Emulsion

Easy Simple Many Uniform and small Dependent on the carriers used and temperature

More difficult Simple Few Uniform and large High

Easy More difficult Many Non-uniform and small High

bead diameters ranging from 25 µm to 2 mm. The actual bead size can be controlled by varying the speed of agitation and it also depends on the type of emulsifier used. Probiotics encapsulated via spray-drying technique show lower survival rates during drying and lower stability during storage (Ananta et al. 2005) than those produced by emulsion and extrusion, a result of their exposure to high air temperatures required to facilitate water evaporation.

Effects of Encapsulation on Probiotic Survival This section summarizes the factors affecting the survival of encapsulated probiotics.

Effect of Carrier Matrix on Probiotic Survival Alginate Alginate is a linear heteropolysaccharide of D-mannuronic and L-guluronic acids extracted from various species of algae. The functional properties of alginate as a supporting material are strongly associated with the composition and sequence of L-guluronic and D-mannuronic acids. Divalent cations such as Ca2 preferentially bind to the polymer of L-guluronic acid (Krasaekoopt et al. 2003). Calcium alginate is preferred over all other supporting materials for encapsulating probiotics due to its simplicity, non-toxicity, biocompatibility, and low cost (Sheu and Marshall 1993; Krasaekoopt et al. 2003). Solubilization of alginate gels by sequestering calcium ions and releasing entrapped cells within the human intestines is another advantage. The concentrations of sodium alginate and calcium chloride used to form the beads vary and range between 1 and 3% alginate with 0.05~1.5 M CaCl2 (Prevost et al. 1988; Kearney et al. 1990; Cui et al. 2000; Chandramouli et al. 2004; Krasaekoopt et al. 2004). A very low level of alginate (0.6% alginate with 0.3 M CaCl2) was used to form a gel by Jankowski et al. (1997). Nevertheless, alginate beads formed using low-viscosity alginate solutions lack mechanical and physical stability (Smidsrod and Skjak-Braek 1990; Peirone et al. 1998). The use of alginate, however, is limited due to its low physical stability in the presence of anti-gelling cations such as sodium and magnesium ions (Lee et al. 2004) or chelating agents such as phosphate (Krasaekoopt et al. 2006). The latter share an affinity for calcium, thus destabilizing the alginate gel (Smidsrod and Skjak-Braek 1990). Furthermore, under low pH conditions, cross-linked alginate matrices can undergo degradation of the alginate molecule and subsequent reduction in its molecular weight causing faster release of entrapped active ingredients (Gombotz and Wee 1998).

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Chapter 4

Specially Treated Alginates Coating alginate beads with polycations and cross-linking with barium ions (Ba2+) instead of calcium ions (Ca2) have been suggested for improving the mechanical stability of alginate microcapsules (Thu et al. 1996; Gaumann et al. 2001; Koch et al. 2003; Krasaekoopt et al. 2006). Polycation-coated alginates: Coating alginate beads with polycations such as chitosan and poly-L-lysine has been studied extensively for encapsulating probiotics (Cui et al. 2000; Canh et al. 2004; Krasaekoopt et al. 2004; Lee et al. 2004; Krasaekoopt et al. 2006). Chitosancoated alginate capsules were produced by dropping an alginate solution into a mixture of calcium chloride and chitosan solution (Krasaekoopt et al. 2004). Since chitosan (poly-(2amino-2-deoxy-β-D-glucopyranose)) is positively charged, it forms polyelectrolyte complexes with alginates resulting in the formation of polyanionic polymer membranes which are stable in the presence of calcium chelators or antigelling agents (Smidsrod and SkjakBraek 1990). Zhou et al. (1998) reported that suspending alginate capsules in a low molecular weight chitosan solution reduced cell release by 40%. On the contrary, Lee et al. (2004) indicated that high molecular weight chitosan coating resulted in the highest survival for Lactobacillus bulgaricus in simulated gastric juice and better stability at 22°C. Krasaekoopt et al. (2006) studied the survival of probiotics encapsulated in chitosan-coated alginate beads in yogurt and found that the survival of the encapsulated probiotic bacteria was higher than free cells by approximately 1 log cycle. Lee et al. (2004) indicated that microencapsulation of freeze-dried L. bulgaricus by chitosan-coated calcium alginate greatly improved the viability of probiotics in simulated gastric and intestinal juices. Alginate poly-L-lysine microcapsules’ high biocompatibility and strength make them good candidates for food applications (Champagne et al. 1992; Larisch et al. 1994; Krasaekoopt et al. 2004). Bifidobacteria loaded onto alginate poly-L-lysine microparticles displayed enhanced survival of the probiotic bacteria during storage at 4°C (Cui et al. 2000). Krasaekoopt et al. (2004) compared the survival of microencapsulated probiotics using different coating materials and found that chitosan-coated alginate beads provide better protection for Lactobacillus acidophilus and Lactobacillus casei than did poly-L-lysinecoated alginated beads in 0.6% bile salts. Modification of alginates by succinylation (increased matrix anionic charge) or by acetylation (increased matrix hydrophobicity) has also been suggested for stabilizing encapsulated probiotics in acidic conditions (Le-Tien et al. 2004).

Prebiotics-Coated Alginates Prebiotics are non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon (Gibson and Roberfroid 1995). Several studies (Bielecka et al. 2002; Chen et al. 2005a) have confirmed that incorporation of prebiotics and calcium alginate as coating materials provides better protection for probiotics in food and eventually the intestinal tract. Chen et al. (2005a) incorporated prebiotics as coating materials for probiotic microencapsulation and demonstrated that the addition of fructooligosaccharides (FSO), isomaltooligosaccharides (IMO), and peptides in the walls of probiotic microcapsules provided improved protection for the active organisms. Probiotic counts remained at 106107 cfu g-1 for microcapsules stored for one month and were then subjected to a simulated gastric fluid test



91

and a bile salt test. Iyer and Kailasapathy (2005) reported that addition of Hi-maize starch to capsules containing Lactobacillus spp. provided maximum protection under acidic condition. Moreover, by further coating the capsules with chitosan, the survival rate was significantly increased under acidic and bile salt conditions. Gellan Gum and Xanthan Gum Gellan gum, a microbial polysaccharide derived from Pseudomonas elodea, is constituted of a repeating unit of four monosaccharide molecules (glucose, glucuronic acid, glucose, and rhamnose). The combination of gellan and xanthan gums to form bead is not only acid resistant but also is stabilized by calcium ions (Norton and Lacroix 1990), which can protect cells from acid injury. Sun and Griffiths (2000) encapsulated Bifidobacterium spp. with gellan-xanthan gum as the coating material and reported that gellan-xanthan beads were highly acid-stable. At pH 2.5, the viable count of encapsulated probiotics decreased by only 0.67log in 30 min. while the survival of free cells dropped from 1.23 109 cfu mL-1 to an undetectable level in the same period. -Carrageenan and Locust Bean Gum -Carrageenan is a natural polymer extracted from Irish moss and is commonly used in the food industry. Formation of a gel using this polymer occurs because of temperature changes. The cell suspension is mixed with the heat-sterilized polymer solution at 40–50°C and gelation occurs on cooling to room temperature. The microcapsules are stabilized by adding potassium ions. The encapsulation of Bifidobacterium bifidum in -carrageenan beads maintained the cell viability for as long as 24 weeks of cheddar cheese ripening, with no negative effects on the texture, appearance, or flavor (Dinakar and Mistry 1994). However, -carrageenan produces brittle gels which are not able to withstand stresses of internal bacterial growth and shear during agitation (Audet et al. 1988). The combination of -carrageenan with locust bean gum, which produces more flexible gels due to specific interactions between the two gums, was recently used to encapsulate probiotics. The probiotics suspension was mixed with a -carrageenan-locust bean gum solution, and the cell-polymer dispersion was then rapidly poured into vegetable oil with agitation. The beads were washed and soaked in sterile KCl solution. Several researchers (Maitrot et al. 1997; Audet, et al. 1988) combined -carrageenan with locust bean gum as supporting material for encapsulation of probiotics and found that this coating material was less sensitive to acid than alginate. Guoqiang et al. (1991) reported that a mixed gel matrix of -carrageenan and locust bean gum showed significant stability for 3 months in continuous lactic acid fermentation. However, the encapsulation of probiotics using -carrageenan-locust bean gum as support material required potassium ions which can damage cells of the probiotic bacteria (such as Streptococcus thermophilus, L. bulgaricus, and Bifidobacterium longum) during fermentation (Audet et al. 1988). Furthermore, large amount of potassium ions are not recommended in human diet. Cellulose Acetate Phthalate Cellulose acetate phthalate (CAP) is an enteric coating material used for controlling drug release in the intestines and thus has a well-established safety record for pharmaceutical

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Chapter 4

and dietary supplements applications. CAP is not soluble in water at pH values of less than about 5.8. The advantage of CAP is that it is insoluble at acidic pH (less than 5) but is soluble at pH greater than 6. Nevertheless, encapsulation of bifidobacteria by CAP was found to be ineffective in preventing acid injury to bacteria in highly acidic yogurt (Modler and Villa-Garcia 1993). Fávaro-Trindade and Grosso (2002) encapsulated Bifidobacterium lactis and Lactobacillus acidophilus using CAP as the coating material and concluded that CAP provided good protection for both microorganisms in acid and bile solutions, conditions similar to those of the intestine. Chitosan Chitosan is a cationic linear polysaccharide composed essentially of β(1-4)-linked glucosamine units together with some proportion of N-acetylglucosamine units. Droplets of a chitosan solution suspended in an oil phase can be hardened by cross-linking with glutaraldehyde (suspension cross-linking) via solvent evaporation or by the addition of polyvalent anions such as sodium tripolyphosphate (TPP) or citrate (ionotropic gelation). The stirring rate, temperature, level of the gelling agent, concentration of the surfactant polymer, and the viscosities of the phases were reported to affect the size and morphology of the particles (Peniche et al. 2003). However, inhibitory effects of chitosan on different types of lactic acid bacteria were reported by Groboillot et al. (1993). Others Lian et al. (2002) investigated the survival of bifidobacteria after spray-drying with different carrier matrices and indicated that the survival of microencapsulated bifidobacteria after spray-drying varied with strains and was mainly dependent on the carriers used. In addition, use of 10% gelation, gum arabic, and soluble starch resulted in the highest survival of bifidobacteria. O’Riordan et al. (2001) used modified waxy maize starch to encapsulate Bifidobacterium spp. with an average size of 5 µm by spray-drying and demonstrated that maximum recovery yields were 30%. However, the starch-encapsulated Bifidobacterium spp. showed no improvement in viability compared with the control-free cells when exposed to acidic conditions or when added to yogurt. They concluded that the modified starches might not be suitable for use as an encapsulating material for probiotic strains. Ananta et al. (2005) incorporated oligofructose-based or polydextrose-based skim milk in a carrier matrix which resulted in a high level of survival for Lactobacillus rhamnosus (LGG). A probiotic survival rate of 60% was achieved at an outlet temperature of 80°C. Desmond et al. (2002) studied the survival of Lactobacillus paracasei in a mixture of reconstituted skim milk and gum acacia followed by spray-drying and found ten-fold greater survival than in the control group. Hou et al. (2003) developed a technique to protect lactic acid bacteria against simulated gastrointestinal conditions by encapsulating bacterial cells within artificial sesame oil emulsions.

Effect of Spray-Drying on Probiotic Survival The survivability of the encapsulated probiotics is most significantly influenced by the execution of the spray-drying process as well as other factors. The survival of various lactic



93

cultures affected by spray-drying have been carried out by various investigators (O’Riordan et al. 2001; Lian et al. 2002; Lian et al. 2003; Picot and Lacroix 2003, 2004; Ananta et al. 2005). Different polysaccharides were used as the matrix and the nozzle temperature of the spray dryer as well as the water activity of the microcapsules had a considerable impact on the survival of probiotics. The heat resistance of probiotic strains should be taken into account during the spray-dry encapsulation of sensitive microorganisms. Picot and Lacroix (2004) dispersed fresh cells in a heat-treated whey protein suspension followed by spray-drying and found a survival rate of 26% for Bifidobacterium breve after spray-drying and 1.4% for the more heat-sensitive B. longum. Lian et al. (2002) studied the survival of bifidobacteria after spray-drying and found that Bifidobacterium longum B6 exhibited the least sensitivity to spray-drying and showed the highest survival of 82.6% after drying with skim milk. The outlet-air temperature is another major parameter affecting probiotic survival after spray-drying with lower temperatures resulting in higher survival rates (Favaro-Trindade and Grosso 2002; Ananta et al. 2005; Chen et al. 2006). Lian et al. (2002) reported that Bifidobacterium spp. had the highest survival after drying at 50°C. Chen et al (2006) studied the viability of probiotics after spray-drying at outlet air temperatures of 60, 70, and 80°C and found that the survival of L. acidophilus and B. longum decreased as the outlet-air temperature increased. However, the final total probiotic counts still remained above the recommended therapeutic minimum (107 cfu/g) after spray-drying at various outlet air temperatures. Gardiner et al. (2002) spray-dried L. paracasei NFBE 338 Rifr with 20% reconstituted skim milk at air inlet and outlet temperatures of 175°C and 68°C, respectively, and found a probiotic survival rate of 84.5%. Ananta et al. (2005) assessed probiotic injury sites in spray-drying by flow cytometry and found that the damage to cell membranes was the key reason for cell death. Higher outlet temperature used for spry-drying resulted in more serious disintegration of membranes. On the other hand, inactivation caused by increased outlet-air temperatures varied with the carrier used. Lian et al. (2002) indicated that using soluble starch as the carrier matrix significantly improved the probiotic survival at a high outlet-air temperature, whereas skim milk showed the least effect.

Probiotic Survival in Dairy Products An adequate number of viable cells, namely the “therapeutic minimum,” need to be consumed regularly in order for consumers to experience the probiotic effects. Encapsulation has been investigated for improving the viability of the microorganisms in dairy products including fermented milk (Adhikari et al., 2000; Sultana et al. 2000; Sun and Griffiths 2000; Adhikari et al. 2003; Krasaekoopt et al. 2004; Picot and Lacroix 2004; Iyer and Kailasapathy 2005), cheese (Dinakar and Mistry 1994; Desmond et al. 2002), and frozen desserts (Sheu and Marshall 1993; Shah and Ravla. 2004). Cheese Introducing encapsulated probiotics in cheese not only enhances the storage viability of probiotics but also improves the flavor of cheese. Research results (Dinakar and Mistry 1994; Desmond et al. 2002) have reported that cheese containing encapsulated Bifidobacterium spp. and L. paracasei did not differ from the control cheese in soluble protein, flavor, appearance, texture, and normal microflora. The viabilities of both encapsulated

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Chapter 4

Bifidobacterium spp. and L. paracasei in cheese were maintained for at least 6 months and 3 months, respectively. In addition, acetic acid, a common metabolite of Bifidobacterium spp. and not preferred in dairy products, was not detected during ripening. Frozen Dairy Desserts It is difficult to incorporate probiotic bacteria into frozen desserts due to the acidity of the products, high osmotic pressure, freeze injury, and exposure to air, as air is introduced during freezing of these products (Shah and Ravla 2004). Thus, the application of microencapsulated probiotic bacteria to frozen dairy desserts may overcome these difficulties and could produce useful markets and health benefits. Sheu et al. (1993) studied the survival of culture bacteria in frozen desserts and indicated that the survival rate for encapsulated L. bulgaricus in continuously frozen ice milk was approximated at 90% without a measurable effect on the sensory characteristics. Yogurt Incorporation of probiotics has been shown to enhance the therapeutic value of yogurt. However, the survival of probiotics in yogurt is low due to the prevailing low pH ranging from 4.2 to 4.6 (Kailaspathy and Rybka 1997). Many studies have documented the positive effects of encapsulation of probiotics and their survival in fermented dairy products (Adhikari et al. 2000; Sultana et al. 2000; Sun and Griffiths 2000; Adhikari et al. 2003; Krasaekoopt et al. 2004; Picot and Lacroix 2004; Iyer and Kailasapathy 2005). Of all encapsulation techniques tested, chitosan-coated alginate beads were reported to offer no enhanced protection for probiotics in yogurt stored at 4°C for 4 weeks (Krasekoopt et al. 2006).

Probiotic Survival in Gastrointestinal Conditions Encapsulated probiotics should survive passage through the upper digestive tract in large numbers in order to ensure desired beneficial effects in the host intestines (Gilliland 1989). Various effects of encapsulation on the survival of bacteria under gastrointestinal conditions have been reported (Table 4.5). The survival of encapsulated cells is strongly dependent on the type and concentration of coating materials, bead size, initial cell numbers, and bacterial species. Most studies have proven the advantages of encapsulating probiotics over free cells under in vitro gastric conditions, others did not find any additional protection under strongly acidic conditions (Rao et al. 1989; Sultana et al. 2000; O’Riordan et al. 2001; Truelstrup et al. 2002). Several coating materials including sodium alginate (Lee and Heo 2000; Chandramouli et al. 2004), sodium alginate with a polycation (Cui et al. 2000; Krasaekoopt et al. 2004; Lee et al. 2004; Iyer and Kailasapathy 2005), gellan/xanthan gum (Sun and Griffiths 2000; McMaster et al. 2005), artificial oil (Hou et al. 2003), gum arabic (Lian et al. 2003), and whey protein (Picot and Lacroix 2004) showed good protection for encapsulating probiotics under gastrointestinal conditions. Lee and Heo (2000) studied the survival of B. longum immobilized in alginate beads in simulated gastric juices and bile salt solutions and found that the death rate of the probiotics in the capsules decreased proportionally with an increase in the alginate concentration (13%), bead size (13 mm), and initial cell

Artificial oil 30% gelatin 35% soluble starch 35% gum Arabic 15% skim milk 30% gelatin 35% soluble starch 35% gum Arabic 15% skim milk 1% alginate with microporous glass membrane 1.8% sodium alginate 2% sodium alginate with chitosan Alginate PLL-alginate 2% sodium alginate with chitosan Alginate PLL-alginate 2% sodium alginate with chitosan 10% heat-denatured whey protein isolate

Extrusion Spray-drying Emulsion

Emulsion Spray-drying

Spray-drying

Emulsion Extrusion Extrusion

Extrusion

Extrusion Emulsion/spray-drying

B. infantis

L. casei

L. acidophilus L. acidophilus

L. casei

L. bulgaricus B. breve B. longum L. acidophilus

B. lactis

0.75% gellan/1% xanthan gum 10% starch 3% alginate

Emulsion

L. acidophilus Bifidobacterium spp. B. infantis B. ruminantium B. adolescentis B. breve B. lactis B. longum L. bulgaricus B. longum

Extrusion

Extrusion

2% sodium alginate with poly-L-lysine or chitosan 2% alginate with Hi-maize starch

Extrusion

B. bifidum

Sodium alginate with poly-L-lysine or chitosan Addition of Hi-maize starch or Raftiline®/Raftilose® 0.75% gellan/1% xanthan gum

2–4% sodium alginate

Extrusion

B. longum

Coating materials

Encapsulation method

Sun and Griffiths (2000) O’Riordan et al. (2001) Truelstrup et al. (2002)

Hou et al. (2003) Lian et al. (2003)

Higher than 106 cfu mL–1 No counts detectable 8.2–1.0 log cfu mL–1

Higher than 106 cfu mL–1 87.15% 95.47% 93.53% 81.26% 92.73% 92.70% 89.17% 65.16% Higher than 106 cfu mL–1

Higher than 106 cfu mL–1

105–106 cfu mL–1 1.5 × 106 cfu g–1 1.3 × 104 cfu g–1 1.0 × 104 cfu g–1 1.6 × 106 cfu g–1 6.7 × 103 cfu g–1 7.0 × 103 cfu g–1 Higher than 106 cfu mL–1 1.0log cfu mL–1 3.8log cfu mL–1 Higher than 106 cfu mL–1

Sultana et al. (2000)

Higher than 106 cfu mL–1

McMaster et al. (2005)

Iyer and Kailasapathy (2005)

Lee et al. (2004) Picot and Lacroix (2004)

Krasaekoopt et al. (2004)

Chandramouli et al. (2004) Krasaekoopt et al. (2004)

Song et al. (2003)

Lian et al. (2003)

Cui et al. (2000)

Lee and Heo (2000)

Reference

Depending on alginate concentration and bead size Higher than 106 cfu mL–1

Survival under gastrointestinal conditions

The effect of encapsulation on the survival of bacteria under gastrointestinal conditions

Probiotics

Table 4.5.


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numbers. Similar results were also observed by Chandramouli et al. (2004). Furthermore, Sultana et al. (2000) reported that survival of probiotics in alginate-starch beads with diameters of 1.0 mm did not improve after exposure to acidic and bile salt solutions.

Applications of Modern Optimization Techniques on the Optimal Manufacturing Conditions for Probiotic Capsules Factors that can influence the survival rate of the probiotic capsules have been discussed in the above sections. Different ingredients constituting the probiotic capsules may also have profound effects on the survival rate. In order to clarify the effects of these different ingredients, experimental design can be carried out and response surface models developed. Furthermore, modern optimization techniques can be applied to attain the optimal composition of the capsules. The objective of this section is to demonstrate the application of two modern optimization techniques for searching the optimal combination of coating materials for probiotic microcapsules. The whole concept (Figure 4.1) includes: 1. 2. 3. 4. 5.

Performing screening experiments and experimental design Encapsulating the probiotics according to the experimental design Building response surface models and formulating the optimization model Performing optimization Verifying the optimal manufacturing conditions.

A practical example of incorporating an additional prebiotic component to alginate matrix is presented in the following to illustrate the entire scheme.

Performing Screening Experiments and Experimental Design Theoretically, all factors that affect the physicochemical properties of a final product should be included in the experimental design. However, if all the variables are included, the search process may become cumbersome. Therefore, the potentially dominant parameters must be identified by a screening process to limit the number of experiments needed to a reasonable extent. After the screening experiments, the remaining screened factors are used in the design. The experimental design, which applies the statistical principles for data collection prior to the experiment, has the main advantage of reducing the number of experimental trials needed to evaluate multiple parameters and to determine their interactions (Porretta et al. 1995; Lee et al. 2000; Chen et al. 2005b). The response surface design, including the Central Composite Design (CCD) and Box-Behnkin Design (BBD; Box and Behnkin 1960) provides more informative data from the least number of experimental runs than from the traditional method. The CCD is a popular class of second-order design. This design involves the use of a two-level factorial and 2k axial points with k being the number of factors involved. On the other hand, the BBD is an effective three-level design based on the construction of a balanced incomplete block design, and is an important alternative to CCD. In this study, survival of encapsulated probiotics (Lactobacillus spp. and Bifidobacterium spp.) was found to be dependent on the concentrations of alginates as well as the



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Figure 4.1. Research scheme for application of modern optimization techniques for encapsulating probiotics.

three prebiotic coating materials (peptides, FOS, and IMO). These four components were regarded as independent variables and therefore a four-variable BBD with six replicates at the center point (total 30 trials) was selected to build the response surface models. The coded and the nature variables and their respective levels are shown in Table 4.6.

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Table 4.6.

Process variables and their levels in four variables—Box Behnkin Design Level

Independent variable

Symbol

Sodium alginate concentration (%)

X1

Peptides concentration (%)

X2

FOS concentration (%)

X3

IMO concentration (%)

X4

Coded

Nature

–1 0 +1 –1 0 +1 –1 0 +1 –1 0 +1

1.00 2.00 3.00 0.00 0.50 1.00 0.00 1.50 3.00 0.00 1.50 3.00

Encapsulating the Probiotics According to the Experimental Design A schematic representation of the manufacturing process for probiotic microcapsules is shown in Figure 4.2 and the process can be described as follows. Probiotic microcapsules were prepared according to the BBD by mixing 4% (v/v) of culture concentrate (1% each of L. acidophilus, L. casei, B. bifidum, and B. longum) with sodium alginate and the previously autoclaved (121°C, 15 min) prebiotics, FOS (03%), and IMO (03%), as well as

Figure 4.2.

Flow diagram for the preparation of probiotic microcapsules.



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peptides (01%). The mixture with cell suspension was injected through a 0.11 needle into sterile 0.1 M CaCl2. The beads approximately 0.5 mm in diameter were allowed to stand for 1 hr for solidification, and then rinsed with, and subsequently kept in, sterile 0.1% peptone solution at 4°C. Survival of the microencapsulated probiotics before and after simulated gastric fluid test (defined as responses) was determined. The four responses were defined as viability of Lactobacillus spp (L. acidophilus + L. casei.) before simulated gastric fluid test (SGFT), viability of Bifidobacterium spp. (B. longum + B. bifidum) before SGFT, viability of Lactobacillus spp. after SGFT, and viability of Bifidobacterium spp after SG

Building Response Surface Models and Formulating the Optimization Model Experimental data can be utilized to build mathematical models using linear, quadratic, or cubic functions by the least square regression method, after which the fitted functions are tested for adequacy and fitness using analysis of variance (ANOVA). Once an appropriate approximating model has been derived, it can then be analyzed using various optimization techniques to determine the optimum conditions for the process. Model analysis and the Lack-of-Fit test can be used for the selection of adequate models, as outlined by Lee et al. (2000) and Weng et al. (2001). The model analysis compares the validities of the linear, quadratic, and cubic models for the different responses according to their F-values. A model with P-values (P>F) below 0.05 is regarded as significant and the highest-order polynomial that is significant will be selected. The Lack-of-Fit test demonstrates if the lack-of-fit between the experimental values and those calculated based on the model equations can be explained by the experimental error. The model with no significant lack-of-fit is appropriate for the description of the response surface. In this example, the model analysis results (Table 4.7 and Table 4.8) show that the following four equations, which represent three linear survival models (Lactobacillus spp. before SGFT, Bifidobacterium spp. before SGFT and Bifidobacterium spp. after SGFT) and one cubic model (Lactobacillus spp. after SGFT), appear to be the most accurate with no significant lack-of-fit.

Table 4.7. Model analysis and lack-of-fit test for the viability of lactic acid bacteria for before simulated gastric fluid test La Source Linear Quadratic Cubic

Bb

Model analysisc (P>F)

Lack-of-Fit testd (P>F)

Model analysis (P>F)

Lack-of-fit test (P>F)

0.0002** 0.5377 0.5023

0.3972 0.3595 0.2509

0.0013** 0.4090 0.6494

0.8444 0.8743 0.9092

* Significant at 5% level. ** Significant at 1% level. a L: L. acidophilus L. casei. b B: B. longum B. bifidum. c Model analysis selects the highest order polynomial where the additional terms are significant. d Lack-of-Fit test wants the selected model to have insignificant lack-of-fit.

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Table 4.8. Model analysis and Lack-of-Fit test for the viability of lactic acid bacteria for after simulated gastric fluid test L Source


Linear Quadratic Cubic

0.0004** 0.0161* 0.0006**

B Lack-of-fit test (P>F) 0.0812** 0.0631** 0.1421


Lack-of-fit test (P>F)

0.0292* 0.2185 0.2918

0.4182 0.4976 0.6442

* Significant at 5% level. ** Significant at 1% level. L f bef 8 . 17 0 . 075 X 1 0 . 13 X 2 0 . 024 X 3 1 . 05 × 103 X 4

(1)

B f bef 7 . 71 − 0 . 098 X 1 0 . 46 X 2 0 . 021 X 3 3 . 45 103 X 4

(2)

L 1.41 3.53X 8.89X 1.35X 0.68X 0.83X 2 1.19X 2 faft 1 2 3 4 1 2 0.23X 23 0.074X 24 5.89X1X2 0.029X1X3 0.65X1X4 1.46X2 X3 0.81X2X4 0.14X3X4 1.34X1X1X2 0.076X1X1X3 0.17X1X1X4 0.20X1X2X2 0.093X1X3X3 0.085X2X2X3 0.74X 2 X2 X4 0.48X2X3X3 (3) B 7.35 0.045X 0.30X 0.065X 0.065X f aft 1 2 3 4

(4)

L , f B , f L , and f B represent the functions for the survival of Lactobacillus spp. where f bef bef aft aft (superscript L) and Bifid obacterium spp. (superscript B) before (subscript bef) and after (subscript aft) SGFT, respectively. The three-level BBD is incapable of forming the pure cubic terms, that is, those with X3i, and equation (3) confirms this fact. In order to search for a solution maximizing multiple responses, a composite fitness function (CFF) is defined as following:

⎛ CFF = ⎜ ⎝

m

∏ i =1

⎞ fi ⎟ ⎠

1

m

(5)

where fi represents the ith function (response) and m denotes the total number of functions. The term inside the parentheses in equation (5) is the product of all m functions. The composite function combines m responses (m = 4 in our study) into one single function whose maximum can then be sought by optimization techniques with each response contributing equally to the CFF. The relationship between the factors and the responses can be investigated by examining the CFF contour plots created by holding constant two of the four independent variables.



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By fixing the peptides and FOS at three different levels, a three-dimensional plot of CFF values as a function of sodium alginate and IMO can be produced. Figure 4.3 depicts that the CFF values increase in accordance with the higher levels of FOS and peptides. On the other hand, the higher IMO and alginate concentrations lead to lower CFF values when FOS and peptides are 3 and 1%, respectively. Figure 4.3(c) shows clearly an optimal CFF value of 8.172.

Performing Optimization The CFF in equation (5) can be used as the objective function to be maximized in an optimization problem, and the problem can be solved to find the optimal formulation for probiotic microcapsules using optimization techniques. Optimization theory consists of a body of numerical methods for finding and identifying the best candidate from a collection of alternatives without having to explicitly evaluate all possible alternatives (Reklaintis et al. 1983). Among the optimization techniques, the steepest ascent (or descent) is commonly used (see, for example, Stat-Ease, Inc., 2000), but the method is relatively inefficient and is a local optimization technique capable of finding only local optima. Genetic Algorithms (GAs), although even less efficient than the steepest ascent, are considered as global schemes. The Sequential Quadratic Programming (SQP) technique is very powerful and efficient, and with some modifications it can also perform global optimizations (Chen 2003).

Optimization Using the SQP Technique A quadratic programming (QP) problem is an optimization problem involving a quadratic objective function and linear constraints. The SQP method represents the current state-ofthe-art in non-linear programming methods (The Math Work Inc., 2000) and can be used to solve a series of QP problems approximating the original non-linear programming problem. The basic scheme of an SQP technique can be expressed in the following steps (Reklaintis et al. 1983; Chen 2003): Step 1: Set up and solve a QP subproblem, giving a search direction. Step 2: Test for convergence, stop if it is satisfied. Step 3: Step forward to a new point along the search direction. Step 4: Update the Hessian matrix in QP and go to step 1. In order to search for the global optimum, the concept of multi-start global optimization procedure (Snyman and Fatti 1987) may be combined with the SQP method. If F* denotes the global maximum and r, the number of sample points falling within the region of convergence of the current overall maximum F after n points have been sampled, then, under statistically non-informative prior distribution, the probability that F be equal to F* satisfies the following relationship (Chen 2003): Pr[FF*] q(n, r) 1[(n1)!(2nr)!]/[(2n1)!(nr)!]

(6)

A global optimization program equipped with a multi-start SQP technique was coded to solve for the optimal solution in this example. The modified SQP with the multi-start ability,

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(a)

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(b)

(c)

Figure 4.3. Response surface plots of survivability of probiotic microcapsules showing effects of sodium alginate and IMO at constant levels of (a) 0% peptides, 0% FOS, (b) 0.5% peptides, 1.5% FOS, (c) 1% peptides, 3% FOS.

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which is capable of reaching the global optimum with great certainty, has been proven to be a very efficient method (Chen et al. 2004). The program generates a series of uniformly distributed random points for initial search, and then the SQP is applied to find the optimum based on each subsequent initial point. If the probability of locating the global optimum exceeds a preset value (99.99% in this example), the global optimum is considered found. Otherwise, the next random, initial point is generated and the SQP re-executed. A very high probability (>0.9999) in equation (6) was set to ensure the global optimum would be attained. Figure 4.4 shows the evolution of the CFF values for a sequence of randomly generated initial searching points and the optimal points found. The optimization results clearly show that determination of the optima depends on the initial search points

Composite fitness function (CFF)

(a)

Number of function evaluations

Optimal composite function value

(b)

Initial searching point set Figure 4.4. (a) Evolution curve of CFF with 2% alginate, 0.5% peptides, 1.5% FOS and 1.5% IMO as the initial searching point; (b) evolution curve of optimal CFF for randomly generated initial searching point using SQP to identify optimal production conditions for probiotic microcapsules.

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and there are three different local optimal CFF values identified from 20 randomly generated initial points. Of these local optima, the global optimal CFF is 8.172 with 99.99% certainty. The global maximum corresponds to: 8.30log cfu for survival of Lactobacillus spp. before SGFT, 8.01log cfu for survival of Bifidobacterium spp. before SGFT, 8.00log cfu for survival of Lactobacillus spp. after SGFT, and 7.72log cfu for survival of Bifidobacterium spp. after SGFT. The highest optimal CFF value (8.172) was attained for 10 of 20 sets and the optimal point consists of independent variables at X1 1, X2 1, X33, and X4 = 0. In other words, the optimal combination of the coating materials for the probiotic microcapsules is 1% sodium alginate blended with 1% peptides, 3% FOS, and 0% IMO.

Optimization Using the Genetic Algorithms Genetic Algorithms are search procedures that imitate the natural evolution process and can be used for the computation of the global maximum or minimum of a function (Mitchell 1996). Genetic algorithms differ from other search techniques in that they search among a population of points and use probabilistic rather than deterministic transition rules. As a result, genetic algorithms search more globally (Wang 1997). GAs provide a very flexible framework and recently have been regarded as not only a global optimization method but also a multi-objective optimization method in various areas. Generally, the algorithms can be described in the following steps (Goldberg 1989; Mitchell 1996): Step 1: Start with a randomly generated population of chromosomes, each of which defines a combination of the coating materials in this example. Step 2: Calculate the fitness f (x) of each chromosome x in the population, with the fitness being the CFF value of that combination of the coating materials. Step 3: Repeat the following substeps until n offsprings have been created: (i) select a pair of parent chromosomes from the current population, the probability of selection being an increasing function of fitness; (ii) with crossover rate, cross over the pair at a randomly chosen point to form two offsprings; (iii) mutate the two offsprings at a prescribed mutation rate and place the resulting chromosomes in the new population; (iv) replace the current population with the new population. Each iteration of this process is called a generation. The above procedure is called the simple GA (SGA). The Micro Genetic Algorithm (MGA) is a popular modification to SGA to optimize the processing conditions (Chen et al. 2003). The essence of MGA is the lack of mutations and the presence of re-starts. Due to these features, the algorithm converges rapidly to a local or global maximum (Nikitas et al. 2001). The lack of mutations also results in a rapid decrease of the variance of the cost values of the population. When the variance value falls below a certain limit, a restarting process begins in which the chromosome with the highest CFF value is retained and the rest N–1 chromosomes (N is the total number of chromosomes in one generation) are replaced by randomly generated new ones. The efficiency of the algorithms can be examined by the number of function evaluations as follows: Number of function evaluations Number of generations Population size

(7)



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A smaller number of function evaluations indicate a higher efficiency. In the study of alginate microcapsules incorporated with prebiotics, the CFF was optimized using MGA. The initial population consisting of 10 chromosomes (population size) was generated at random and the crossover rate was set to 0.5. The chromosomes with higher CFF values were selected and retained for the next generation. The maximum number of generations was set to 500 for the problem. Figure 4.5 shows the evolution curve of the first 3000 function evaluations in searching for the global, optimal value. The MGA produced rapidly increasing CFF during the early stage of the optimization process consisting of a total of 5000 function evaluations, which is typical for MGA. The chromosomes having the maximum CFF provided the optimal ratio of concentrations of the coating materials. The optimal value (CFF = 8.172) was obtained after 1490 function evaluations during the process.

Verifying the Optimal Manufacturing Conditions After the optimal processing condition is found by the SQP or MGA, repeated experiments based on the condition should be conducted to verify the predicted optimum. The verification results can then be analyzed using ANOVA from the SAS software package (SAS Institute Inc., 1990), with Duncan’s multiple range test for significance to detect differences between predicted values and observed values. In this example, the optimal production condition for the coating composition, derived from the SQP and MGA, was the same. The optimal combination of the coating materials for the probiotic microcapsules is 1% sodium alginate blended with 1% peptides, 3% FOS, and 0% IMO. The four responses (survival of Lactobacillus spp. and Bifidobacterium spp. before and after SGFT) and the CFF value derived from the verification experiments are all very close to the SQP- or MGA-based prediction, with no apparent significant differences (P 0.05) comparing the two sets. Both SQP and MGA techniques may be used to determine the optimal combination of the coating materials for probiotic microcapsules. By comparing both methods, SQP was deemed to be much more efficient than MGA at such a task.

Figure 4.5.

Optimum composite function values using MGA.

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Practical Applications of Encapsulated Probiotics in Dairy Products As discussed above, encapsulated probiotics have been used for accelerating cheese ripening, fortifying dairy products with beneficial bacteria as well as enhancing the shelf life and bioavailability of this class of microorganisms in dietary supplements. Several companies are currently involved in designing and manufacturing such products to meet customers’ needs. Following are few examples of incorporating encapsulated probiotics into real food systems: Yogurt For manufacturing set yogurt, homogenized whole milk and skim milk powder are blended for a total solids content of 15–18%(w/w). The mix is pasteurized at 80–85°C for 30 min. and cooled to 42°C before inoculation with a commercial freeze-dried starter culture containing S. thermophilus and L. bulgaricus. The encapsulated probiotic cultures are then added and the resulting mix is dispensed into containers and incubated at 42°C for 4–5 hr until the pH reached 4.5. Finally, yogurts are stored at 4°C (Adhikari et al. 2000; Sultana et al. 2000; Sun and Griffiths 2000; Krasaekoopt et al. 2004; Picot and Lacroix 2004; Iyer and Kailasapathy 2005). Stirred yogurt is manufactured in the same way except that the mix after inoculation is incubated at 42°C for 4–5 hr until the pH reaches 4.5, added with 10% microencapsulated probiotics, and then stirred and dispensed into containers. The probiotic yogurt is stored at 4°C (Adhikari et al. 2003). The probiotic counts of yogurts remained above 106 cfu/mL and the final pH was 3.9–4.1 after one month of storage. Commercialized yogurt products containing microencapsulated probiotics are also available. Kaung-Chuan Inc. in Taiwan produces a bio-yogurt drink with probiotic microcapsules, which incorporate Bifidobacterium spp, are made by gelatin and have an average size of 1–2 mm. The company claims that this product has intestinal benefits. Cheese Introducing encapsulated probiotics to cheese not only enhances the storage viability of probiotics but also improves the cheese flavor. For manufacturing cheddar cheese, raw whole milk is pasteurized and cooled to 31°C. The freeze-dried mesophilis lactic starter culture is added at the rate of 5 g/100 g of milk. Curd forms in approximately 30 min. and is cut with 0.65 cm wire knives. After a 15 min. healing period, the temperature of the curd and whey mixture is raised to 37–38°C in 30 min. and then maintained at that temperature for an additional 30 min. After the whey is drained, the curd is cheddared to pH 5.2, and then milled, salted, followed by addition of the microencapsulated probiotics and packing into hoops that are further ripened at 7°C for 6 months. Cheese containing encapsulated Bifidobacterium was shown to possess similar flavor, texture, and appearance compared to the control (Dinakar and Mistry 1994; Desmond et al. 2002). Frozen Desserts For manufacturing frozen ice milk, probiotics microencapsulated with 3% calcium alginate (bead diameters > 30 µm) are blended with milk (5% fat) and the mix is frozen continuously



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Figure 4.6. Typical manufacturing process of fermented, frozen dairy desserts with microencapsulated probiotics.

in a freezer. Addition of microencapsulated probiotics has no measurable effect on the overrun and the sensory characteristics of the products with 90% probiotic survival (Sheu et al. 1993). Sheu et al. (1993) manufactured fermented frozen dairy desserts by blending freeze dried microencapsulated probiotics with yogurt and base mix, and then the mix was frozen in a continuous freezer. Figure 4.6 details the process of incorporating encapsulated probiotic culture to a frozen milk-based dessert system.

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Summary Encapsulated probiotics can be used in many dairy products such as yogurt, frozen desserts, and cheese. In the encapsulated form, these sensitive microorganisms are protected from harsh environments including high levels of lactic and acetic acid, gastrointestinal conditions, and freezing temperatures. Among encapsulation methods, spray-drying, extrusion, and emulsion are the most common techniques for probiotic encapsulation. However, the high cost of the process and the technical difficulty limit the large-scale application of encapsulation technologies in the dairy industry. Carrier matrices, encapsulation methods, and various dairy products to which the probiotic capsules are applied can influence the survival rate of the probiotics. Different ingredients constituting the probiotic capsules may also have profound effects on the survival rate. In order to clarify the effects of these different ingredients, experimental design can be carried out and response surface models developed. Furthermore, modern optimization techniques can be applied to attain the optimal composition of the capsules. The two-stage effort of obtaining a surface model using RSM and optimizing this model using SQP and MGA techniques has been demonstrated to represent an effective approach.

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Survival of Bifidobacteria during refrigerated storage in the presence of acid and hydrogen peroxide. Milchwissenschaft 51: 65–70. Larisch, B. C., D. Poncelet and C. P. Champagne. 1994. Microencapsulation of Lactococcus lactis subsp. cremoris. Journal of Microencapsulation 11(2): 189–195. Lee, J. S., D. S. Cha and H. J. Park. 2004. Survival of freeze-dried Lactobacillus bulgaricus KFRI 673 in chitosancoated calcium alginate microparticles. Journal of Agricultural Food Chemistry 52: 7300–7305. Lee, K. and T. Heo. 2000. Survival of Bifidobacterium longum immobilized in calcium alginate beads in simulated gastric juices and bile salt solution. Applied and Environmental Microbiology 66(2): 868–873. Lee, J., L. Ye, W. O. Landen and R. R. Eitenmiller. 2000. Optimization of an extraction procedure for the quantification of vitamin E in tomato and broccoli using response surface methodology. Journal of Food Composition and Analysis 13: 45–57. Le-Tien, C., M. Millette, M. Mateescu and M. Lacroix. 2004. Modified alginate and chitosan for lactic acid bacteria immobilization. Biotechnology and Applied Biochemistry 39: 349–354. Lian, W. D., H. C. Hsiao and C. C. Chou. 2002. Survival of Bifidobacteria after spray-drying. International Journal of Food Microbiology 74: 79–86. Lian, W. D., H. C. Hsiao and C. C. Chou. 2003. Viability of microencapsulated Bifidobacteria in simulated gastric juice and bile solution. International Journal of Food Microbiology 86: 293–301. Maitrot, H., C. Paquin, C. Lacroix and C. P. Champagne. 1997. Production of concentrated freeze-dried cultures of Bifidobacterium longum in k-carrageenan-locust bean gum gel. Biotechnology Techniques 11 (7): 527–531. Martin, J. H. and K. M. Chou. 1992. Selection of Bifidobacterium ssp. for use as dietary adjuncts in cultured dairy foods I. Tolerance to pH of yogurt. Cultured Dairy Products Journal 27: 21–26. Mattila-Sandholm, T., P. Myllärinen, R. Crittenden, G. Mogensen, R. Fonden and M. Saarela. 2002. 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5

Encapsulation and Controlled Release in Bakery Applications Jamileh M. Lakkis

Introduction In commercial baking operations, high volumes of dough and batter premixes are prepared for further distribution to stores and on-site baking. Maintaining good functionality and overall quality of these products requires careful inactivation of the prevailing leavening systems during storage and their controlled reactivation upon preparation and baking. The basic ingredients in doughs and cake batters include flour, fat, eggs, and sweeteners. These components play an important role in determining the functional and eating quality of bakery products. Minor ingredients such as yeasts and chemical leavening agents, however, can have more dramatic effects on the overall quality and shelf life of these products. Recent advances in microencapsulation and controlled release technologies have contributed significantly to current availability and wide consumers’ acceptability of shelfstable bakery products. Bakery manufacturers have been keen on adopting these technologies due to the tremendous cost savings provided by extending shelf life, eliminating fermentation stage, and shortening dough proofing time along with minimal impact on processability of bakery products. These benefits can be better appreciated considering the huge market of bakery products that was estimated at $300 billion worldwide in 2005 (Sosland Publishing Co., Kansas City, MO). This chapter discusses methods for encapsulating and controlling the release of chemical and biological leaveners as well as other functional components of bakery systems such as sweeteners, antimicrobial agents, dough conditioners, and flavors. Microencapsulation technologies as well as coating materials available for bakery applications are also discussed.

Encapsulation Technologies for Bakery Applications A variety of encapsulation technologies have been adapted for bakery applications, mainly hot melt particle coating and congealing via spray chilling. Embedding via extrusion and liposome/vesicles, used to a much lesser extent in bakery applications, has been covered elsewhere in this book; therefore, only particle coating and congealing are discussed here.

Hot Melt Particle–Coating Technology Fluid bed coating is a well-established technology for encapsulating and controlling the release of solid actives. The process consists, essentially, of spraying a solution or a molten fluid onto particles of a substrate material undergoing encapsulation. Application of a film to a solid is a very complex process and requires careful selection of substrates and coating materials as well as process conditions.

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The solid substrate is placed in a container that is typically an inverted truncated cone with a fine retention screen and an air distribution plate at its base. As the warm air flows through the distribution plate, the particles become fluidized and are accelerated in an upward flow where they encounter fine spray of the coating fluid. The coating spray nozzle can be fitted (1) to the top (top-spray system); (2) to the bottom (bottom-spray system referred to as Wurster); or (3) tangential to the base container (Figure 5.1a, b, c). The choice of a suitable coating configuration should take into consideration the type of solid to be coated (powder, pellets, etc.) as well as the desired film thickness and release properties. Top-spray fluid beds are favored for high-throughput applications as well as for film uniformity. Bottom-spray (Wurster) systems are preferred for their high coating effectiveness as well as their ability to form perfectly sealed films. This is critical for controlled release applications. Tangential-spray systems (rotor pellet coating), on the other hand, are suitable for coating pellets and rods (yeasts) but not small particles (sodium bicarbonate and other chemical leaveners). In the tangential coating system, rotation of the base plate disc sets the pellets into a spiral motion where they encounter the coating spray, thus coating concurrently to the powder bed. Very thick film layers can be applied using the rotor configuration. In the Wurster system, film thickness varies with particle size within a batch; top- or tangential-spray fluid beds rarely show this variation. This is due, in part, to the slow circulation of lighter and/or smaller particles, a pattern inherent to the Wurster process (Ichikawa et al., 1996). Regardless of the coating unit configuration chosen, film formation around solid particles cannot be achieved by a single pass through the coating zone, but requires many such passes to produce complete particle coverage. The presence of any loose uncoated actives can also have detrimental effects on the release mechanism and overall stability of the finished product. Figure 5.2 shows a schematic of the steps involved in particle coating and film formation in a fluid bed–coating unit. Coat integrity and subsequent release of the active require careful combination of several parameters such as air velocity, air temperature, spray rate, spray droplet size and so on. Jozwiakowski et al. (1990) published an excellent paper detailing the impact of substrate’s physicochemical properties on coating quality and efficiency in a fluid bed system. Their study highlighted the importance of two types of interactions, namely (a)

(b)

(c)

Top spray

Bottom spray (Wurster coating)

Tangential spray (rotor pellet coating)

Figure 5.1. Various configurations of fluid bed–coating systems: (a) top spray, (b) bottom spray (Wurster) and (c) tangential spray. (Courtesy of Glatt Air Techniques, with permission.)


Encapsulation and Controlled Release in Bakery Applications

Spraying

Wetting

Congealing

Particle coating droplets

115

Coated particle

Film formation

Figure 5.2. Film formation principle in a fluid bed–coating system. (Courtesy of Glatt Air techniques, with permission.)

particle–particle and particle–machine, and concluded that an ideal substrate should possess essential attributes such as spherical shape, uniform (high) bulk density, narrow particle size distribution, and chemical stability. Effect of Substrate’s Physicochemical Properties It is critical to point out that film coating in a fluid bed system is applied on a weight basis. Therefore, to achieve same film thickness, larger amounts of shell material are needed to coat small particle cores (Madan et al. 1974). Coat thickness has been shown to be directly related to substrate’s particle diameter but inversely proportional to its surface area (Table 5.1). Particle shape, porosity, and friability can also play an important role in determining film quality. Irregular-shaped particles such as crystals (salts, sodium bicarbonate) require larger amounts of coating (in excess of 80% of microcapsule’s weight) and can most often lead to nonuniform film formation. In coating applications, particle–particle interactions manifest themselves in two different phenomena, agglomeration and attrition. Fluidization of wet fine particle cores (<100 µm diameter) under intensive motion in the bed vortex can lead to particle–particle collision and agglomeration. The latter can be dramatically magnified when the fluid bed is operated at temperatures too close to the melting temperature of the coating material or when using very high rates of spray coating. Ideal core particle size for fluid bed encapsulation ranges from Table 5.1. Effect of particle size on wall thickness. (Adapted from Madan et al., 1974, with permission from the publisher.)

Particle diameter (µm) 235 505 715 840

Calculated surface area of particles

Number of particles (n 10–4)

Wall thickness, T (µm)

624 414 292 249

17.7 5.17 1.82 1.12

0.26 0.02 0.49 0.03 0.64 0.02 1.31 0.13

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100 to 800 µm (assuming optimal bulk density). Larger size particles or pellets (>1 mm) can be coated readily, their repeated cycling in the bed may lead to particle abrasion and attrition. Such cores should be coated for only short time intervals with minimum bed movement during the warming period (Lehmann and Dreher, 1981). Figure 5.3 shows a scanning electron micrograph of typical coated particle surrounded by a lipid/wax wall material with the substrate particles completely engulfed in the lipid/wax shell. Spray Chilling Fluid bed coating described above is, in essence, an enrobing mechanism whereby one or few particles (100–400 µm) are enveloped in a coating film, forming a reservoir-like system. As the temperature surrounding the capsule reaches the melting point of the wall material, the entrapped particles are released. However, in the presence of slightest imperfections in the shell material, the actual release tends to shift to “burst-like” behavior. The latter can have detrimental consequences upon storage and preparation of dough or batter systems, resulting in premature or uncontrolled release of the encapsulated active. Spray chilling is an alternative technique that has been used for years in manufacturing stable pharmaceutical capsules with a unique matrix release mechanism. This technique is a solvent-free spray-drying method for encapsulating water-sensitive actives. In this process, fine particles (typically <100 µm) are dispersed in a hot melt fluid (waxes, fatty acids) to form a homogeneous dispersion. The latter is atomized via spraying through a pressurized single nozzle into a cooled chamber. The chamber temperature is set below the melting point of the mixture or its individual components using nitrogen or carbon dioxide gas. Ideally, spray chilling results in the formation of uniform spherical micropellets with smooth surfaces that are water-impermeable but not water-resistive. These qualities are essential for better mixing owing to reduced surface tension between the microcapsule’s hydrophobic surface and the batter’s aqueous environment. Due to the absence of solvent

Figure 5.3. Surface morphology of a coated solid particle. (Courtesy of Balchem Corp., with permission.)



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evaporation in spray chilling operations, the particles are generally non-porous and mechanically-strong so that they remain intact upon agitation (Gherbre-Sellassie, 1989). Nanosized particles can also be prepared using this process (Eldem et al., 1991). Additional coating is often applied to spray chilled congealed particles to ensure complete coverage of the microparticle and to eliminate undesirable interactions of exposed actives with their surroundings during storage and dough/batter preparation. Conventional spray dryers with cooled air inlets can be used for spray chilling. The apparatus consists of two main parts: (1) a cooling chamber and (2) an atomizer. For effective spray chilling, it is recommended that the dispersion matrix has a very narrow melting range so that the particles can be held together during spraying. Critical conditions for manufacturing uniform congealed capsules are: (1) low viscosity of the active and molten fat dispersion. Das and Gupta (1988) suggested that an ideal viscosity should be around 24 cP at 55°C and (2) high atomization speed to increase the percentage of small micropellets (Scott et al., 1964; Deasey, 1984). Release of actives from spray chilled microcapsules takes place via erosion and leaching through the matrix. Surfactants (depending on type and concentrations) can also dramatically affect matrix dissolution rates. John and Becker (1968) demonstrated that addition of 4% of the non-ionic surfactant sorbitan monooleate resulted in enhanced release rates from a wax-congealed matrix; however, increasing the monooleate concentration to 10% led to a reduction in rate of release. Spray chilling suffers from one main drawback, that is, the rapid cooling rates can sometimes crystallize the triglyceride matrix in the unstable α-polymorphic form, leading to the formation of disordered chains with undesirable orientation and, subsequently, low barrier properties. High-Pressure Congealing (Beta Process) To overcome these drawbacks, a modified method was advanced by Verion Inc. (Redding, 1995; Vaghefi et al., 2001). The process involves forming an active-matrix dispersion (e.g., sodium bicarbonate dispersed in molten fat or wax) and further subjecting the mixture to high pressure (40,000–50,000 psi) for few seconds to intimately compress the mixture. The sodium bicarbonate/fat mixture is then discharged through a spray nozzle into a chilling zone to congeal the molten fat material around the particles. The mixture is allowed to cycle through the system for multiple passes depending on the active load and/or desired capsule matrix consistency. The high pressure and high shear applied result in favorable changes in the polymorphic structure of the treated fat or wax and in shifting its polymorphic structure into the stable beta (β)-form, thus the name Beta process. Redding (1995) studied the impact of heat, pressure, and their combinations on changes in the differential scanning calorimetric (DSC) profiles of tristearin (Figure 5.4) using the β-process system. Commercially obtained native triglyceride displayed a β-melting peak at 72°C. Upon melting and further resolidification, the DSC profile showed, in addition to the β-peak, a new peak at 59.84°C corresponding to the α-form. Heating the tristearin to 145°C along with pressure application (4400 psi) led to the complete elimination of the α-peak and the dominance of a stable β-peak at 75.73°C. Similar to low-pressure congealing, complete coverage of the active particles located on the microparticle surface can be ensured by applying an outer coating layer via fluid-bed or other coating techniques. Capsules prepared, using this process, normally follow true

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Heat flow (w/g)

(a)

72°C 20

40

60

80

100

Temperature (°C)

Heat flow (w/g)

(b) 16 14 12 10

59.84°C

8

77.86°C

6 20

40

60

80

100

60 80 Temperature (°C)

100

Temperature (°C)

(c) Heat flow (w/g)

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20.5 20 19.5 19 18.5 18 17.5 17 20

75.73°C 40

Figure 5.4. Effect of temperature and pressure on polymorphic profile of stearine: (a) native, (b) melted and resolidified, and (c) treated at 145°C and 4400 lb/in.2. (Reproduced from Redding, 1995, with permission from the publisher.)

zero-order release mechanism, a result of the slow erosion from the microcapsules that form “tortuous” paths throughout the matrix. The shell material is not swellable and does not rely on osmotic pressure to release the core material. Film-Forming Materials A variety of fats and waxes are available for hot melt coating of leavening systems (Table 5.2) Lipid-based coating materials are available as pure components or most often as



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Table 5.2. Source and melting temperatures of selected group of waxes, lipids, and resin compounds used in particle-coating applications. (Adapted from various sources.) Product

Source

Melting point (°C)

Beeswax Carnauba wax Candelilla wax Shellac Lauric acid Capric acid Myristic acid Stearic acid Behenic acid Palmitic Stearine Cottonseed oil Stearine Soybean oil

Bees Tree of life Candelilla plant Laccifer lacca insect Coconut oil Coconut oil Coconut oil, butter fat Most fats/oils Peanut oil Most fats/oils Partially hydrogenated

61–64 82–86 65–69 115–120 44 31.6 54.4 69.6 80 62.9 61–64

Partially hydrogenated

66–70

functionally optimized composites (Kanig and Goodman, 1962; Kester and Fennema, 1989a). Blends of lipids (different hydrophobicity, chain length, hardness, melting point, etc.), lipids and waxes, and lipids and polysaccharides can be adequately formulated to encapsulate actives for bakery and other food applications. Waxes Natural and synthetic waxes have been used in particle-coating applications. The most commonly used materials include: paraffin, carnauba, candelilla, beeswaxes and/or wax emulsions. Paraffin wax: Paraffin wax is derived from the wax distillate fraction of crude petroleum. It is composed of hydrocarbon fractions of generic formula CnH2n+2 ranging from 18 to 32 carbon units (Hernandez, 1994). Refined paraffin waxes can be used in specific coating applications (21 CFR, Code of Federal Regulations, 184.1973). Carnauba wax: Carnauba is a plant-derived exudate from the leaves of the Tree of Life (Copernica Cerifera) found mostly in Brazil. Carnauba wax consists mostly of saturated wax acid esters with 24–32 hydrocarbons and saturated long-chain monofunctional alcohols such as myricyl cerotate alcohols C9H59CH2OH. Carnauba wax is the hardest natural wax available (hardness 4.7 cm 102 for a 50 g/60 sec/25oC) and has the highest melting point and specific gravity of commonly found natural waxes (82–86oC). It is added to other waxes to increase melting point, hardness, toughness, and luster. However, carnauba wax is very brittle and lacks elasticity. Carnauba wax is allowed for specific applications in food systems (21 CFR 184.1978). Beeswax: Beeswax is a secretory product of honey bees and is the basic material for comb building. Beeswax is harvested after removal of the honey by draining or centrifuging and further melting with hot water, steam, or solar heating. The wax is separated from impurities by treating with diatomaceous earth and activated carbon. Beeswax is made up essentially of long-chain alcohols (C24–C33), hydrocarbons (C25–C33), and long-chain acids (C24–C34). Beeswax is very plastic at room temperature (melting point 61–65oC) but

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becomes brittle at colder temperatures. It is soluble in most other waxes and oils (Tulloch, 1970; Bennett, 1975). Beeswax is considered a GRAS substance and is allowed for direct use with some limitations (21 CFR 184.1973). Candelilla wax: Candelilla wax is obtained from the candelilla plant that grows mostly in Mexico and southern Texas. The wax is prepared by immersing the plant in boiling water containing sulfuric acid and further skimming off the surface, refining, and bleaching. Its degree of hardness is intermediate between beeswax and carnauba. It contains small amounts of esters and free acids. This wax sets very slowly and takes several days to reach maximum hardness. Candelilla wax is considered GRAS and is allowed for certain food uses (21 CFR 184.1976). Wax macro- and microemulsions: Carnauba and beeswax owing to their high content of alcohol and ether groups, can be microemulsified to form effective coating materials. Waxes are dispersed in water to form macro- or microemulsions via a process commonly known as inversion (Wineman, 1984). Resins and Rosins Shellac: Shellac resin is a secretion by the insect Laccifer lacca and is mostly produced in central India. This resin consists of a complex mixture of aliphatic alicyclic hydroxyl acid polymers, that is, aleuritic and shelloic acids. It is soluble in alcohol and alkaline media. Shellac resins can be blended with waxes to form improved moisture-barrier properties and increased gloss for coated products. Shellac is not GRAS; it is only permitted as an indirect food additive in food coatings and adhesives (21 CFR 175.300). Shellac is rich in carboxylic acid residues and is highly water insoluble (Sward, 1972). Glycol Polymers Polyethylene glycols such as Carbowax (different grades, that is, viscosities 3350, 4600, 8000) possess desirable coating properties, mainly their resistance to abrasion. Levels of 15–40% were found to be useful for coating yeasts and extending their viability (Percel, 1988). Fats and Glycerides A wide variety of commercially available triglycerides are used in coating applications. Naturally occurring food-grade fats are derived from animal or plant origin. Animal triglycerides differ from plant triglycerides not only in the ratios of saturated to unsaturated carboxylic acids or their chain length but also in the location of the unsaturated fatty acid in the glyceryl molecule. Variations in the carboxylic acid chain length, their melting profile, degree of saturation, degree of esterification, purity grades as well as their crystalline structure can have a significant impact on coating processability as well as the performance of the encapsulated product.Natural oils and fats used in coating applications consist of one or more of the three major fatty acid groups; these are lauric, palmitic, and oleic–linoleic groups: Lauric acid group: Fatty acids of this group are highly saturated, rich in short-chain fatty acids (8, 10, and 14 carbon chain length), and are very stable. They contain 40–50% lauric acid on average. Oleic and linoleic acids constitute the majority of the unsaturated



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fractions, while saturated ones are essentially made up of palmitic and stearic acids. Examples of this group include palm seed oil, canola, coconut, babassu, and palm kernel oils. Lauric-acid-based fatty acids have relatively low melting points (~44°C). Hydrogenated canola oil, for example, is composed of a triglyceride with extremely symmetrical, nonrandom structure, resulting in a hard and dry fat with good flowability at room temperature. Coconut oil has melting point of 24°C, while its hydrogenated counterpart melts at 33°C (Bailey, 1952). Palmitic acid group: This group is represented by palm oil (from palm pulp) and palm kernel oil (from kernel). Palm oil contains 32–47% palmitic acid and 40–52% oleic acid. Palm oil has equal concentrations of the saturated and unsaturated fatty acids. Most of the triglycerides (85%) of palm oil contain unsaturated fatty acids at the 2-position of the glycerol backbone (Bailey, 1952). Oleic/linoleic acid group: Commercially important oils in this group include corn, cottonseed, peanut, olive, sunflower, safflower, and rice bran oil. These oils can be hydrogenated to form plastic fats with different degrees of hardness. Most oils in this group are short- and medium-chain unsaturated fatty acids. Only the highly-hydrogenated versions of these fatty acids can be effective in particle coating applications.

Characteristics of Wax and Fat-Coating Materials Chain Length Long-chain fatty acids such as stearic (C 18:0) and palmitic (C 16:0) acids, by virtue of their high melting and apolar properties, have been used extensively in food coating applications (Hagenmaier and Baker, 1991; Greener and Fennema, 1993; Kester and Fennema, 1989b; McHugh and Krochta, 1994). Due to their strong H-bonding, long-chain fatty acids such as stearyl alcohols, stearic acid and beeswax crystallize into platelet-like dense microstructures, commonly associated with effective moisture barrier properties (Figure 5.5). Longer-chain triglycerides (higher than 18 carbon atoms) such as arachidonic or behenic acids, however, show higher permeability presumably due to the heterogenous structure of the polymer network. Polarity Stearyl alcohol, a polar molecule, is a better barrier than its fatty acid counterpart, a result of the lower affinity of the hydroxyl group for water than carbonyl and carboxyl groups. However, in most applications, other factors such as chain structure and its conformation should be taken into consideration when choosing a lipid barrier material. Degree of Unsaturation The degree of unsaturation plays a considerable role in defining the crystal structure of triglycerides and their mobility. For example, the area occupied by a molecule of oleic acid in a monolayer film is 0.48 nm2, whereas for stearic acid, it is 0.23 nm2 (Kamper and Fennema, 1984). Despite this fact, oleic acid displays greater mobility owing to the double bond that favors the diffusivity of water molecules compared to stearic acid, which is a fully saturated carboxylic acid (Gontard et al., 1994).

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Figure 5.5. Cross section of wax-coated particle showing platelet-like microstructure. (Courtesy of Balchem Corp., with permission.)

Solid Fat Index Solid fat index (SFI) has been directly related to fat hardness and its spreadability (Bailey, 1952; Vreeker et al., 1992). High solid fat concentration (0–30%) improves barrier properties of fat-based films but increases their hardness (Narine and Margoni, 2002). High solid fats have better barrier properties than their corresponding liquid or semi-solids due to the formation of dense structure and greater volume that limits the diffusion of water (Perron and Ollivon, 1992). However, at very high solid fat concentration, higher than the critical value, permeability could increase due to structural defects within the film. Hydrophobicity Hydrophobicity has been used as a criterion for predicting water barrier properties of fats and waxes. Kester and Fennema (1989a, b) proposed the following order of decreasing moisture barrier effectiveness of waxes and fats: beeswax, stearyl alcohol, acetyl glycerols, hexatriacontane, tristearin, and stearic acid, a reflection of their decreased hydrophobicity. Avner and Blatt (1990) indicated that despite the similarities in melting temperatures between hydrogenated castor oil and calcium stearate/stearic acid blend (melting point~86°C), hydrogenated castor oil provided higher thermal stability and barrier properties due to the superior hydrophobic character of castor oil. Polymorphism (Crystallization Behavior) Triglyceride molecules are naturally arranged in a “tuning fork” structure where three fatty acids are more or less parallel, one pointing in the opposite direction of the others. However, the complexity and flexibility of triglyceride molecules allow different crystalline packing of the same ensemble of molecules, leading to the existence of different polymorphs. During crystal growth, such molecules will pack more easily side to side than end



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to end with glyceryl alcohols. The resulting individual crystals appear needle shaped under the microscope (Bailey, 1952; van de Tempel, 1961). Fat polymorphism, that is, their ability to crystallize under several forms, also affects their barrier efficiency. Triglycerides crystallize into α (hexagonal), β (triclinic), and β′ (mainly orthorhombic) forms. The latter two crystals are stabilized by London forces occurring between the aliphatic chains, which give rise to dense networks. No such forces occur in the α-form. The carbon atom can rotate (small angles), leading to a hexagonal nonstable structure (Sato and Kuroda, 1987 and therein; Ubbelohde, 1978). The β-form, represented by lard and tallow, has the highest melting point and highest order (large and coarse crystals 25–50 µm long). β′-crystals, however, provide the most functional form owing to their small size (less than 1 µm), thin needle-shaped morphology, and interlocking structure (Roberts et al., 2000). Polymorphic states of a substance have different physical properties but on melting yield identical liquids since these states are merely due to differences in packing of the constituent molecules upon crystallization.

Melting Point Most naturally occurring fats show multiple melting points reflected in several melting peaks in their DSC profile. Low melting fats most often result in inferior coating qualities due to their poor flowability and tendency to form clumps. On the other hand, high melting fats such as palm stearine may cause difficulties in spray coating encapsulation due to their stiffness and lack of plasticity. The melting point of polymorphic forms of stearine range from 65°C (α) to 70°C (β′) and 72°C (β) (Bailey, 1952).Low melting lipids are useful for coating heat-labile actives such as yeasts, enzymes, vitamins, probiotic bacteria and so on. High melting lipids, on the other hand, are suitable for encapsulating chemical leavening agents, acids, and other less heat-sensitive actives. Despite the positive impact of high melting fats on fluid bed–coating efficiency, coating performance of a given fat is a function of the melting profile and not necessarily the temperature of the melting peak. It has been a common practice to source pure fats/waxes (fewer components) in order to provide a single narrow-shaped peak; in practice coating conditions, in particular the rate of fat/wax cooling, are as critical in determining the sharpness or broadness of the melting peak. The mechanical properties of lipid-based films can be improved by modifying either the film’s melting profile or its structural properties. Two classes of materials have been used to modify the performance of fats, namely, waxes and plasticizers: 1. Waxes can be successfully used to raise the melting point of natural fats, thereby reducing tackiness and enhancing their coating performance. For such applications, it is critical to maintain the fat/wax blend under continuous mixing and at temperatures slightly above the wax-melting point to avoid wax gravity settling and subsequent plugging of the spray nozzle. In the petroleum industry, the temperature at which wax crystals start to appear when temperature falls to a critical level referred to as wax appearance temperature, WAT (Azvedo and Teixeira, 2002). Prolonged heating of wax/fat mixtures, however, may lead to fat oxidation; therefore caution should be exercised and whenever possible, incorporating antioxidants or blanketing the hot melt container with nitrogen can be very effective in retarding fat oxidation and/or degradation.

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2. Plasticizers such as acetoglycerides, glycerin, monoglycerides, alcohols, phospholipids (lecithins) and ester derivatives of glycerols can be used to lower the melting point of fats and waxes, thus facilitating their atomization from the spray nozzle. Plasticizers can also help in reducing film brittleness and enhancing its flexibility and mechanical properties without any significant impact on the melting point of the wax. Litwinenko et al. (2004) reported that addition of glycerol increased the mean crystal size of fats up to a concentration where the crystal size decreased with increased glycerol concentration (Table 5.3). Films made from molten beeswax are often smooth and uniform, whereas those made with alcohol are rough and irregular with apparent large size globules (Greener and Fennema, 1993). Incorporation of polysaccharide molecules such as ethyl cellulose into fat-based films can be used to provide additional film toughness. The latter is presumably a result of the proper orientation of the wax crystallites parallel to the polysaccharide support base.

Ideal Properties of Encapsulated Particles for Bakery Applications Ideal microcapsules manufactured for baking applications should possess the following essential properties. Good Barrier Properties Fats of large and closely packed crystals are favored for their high moisture barrier properties. As discussed above, barrier properties are a combination of fat/wax chain length, polarity, polymorphic form, film flexibility, and so on. Flexibility Fat crystals form a particular class of soft materials that demonstrate yield stress and viscoelastic properties, that is, plastic-like materials (Narine and Marangoni, 1999; 2002). Waxes, on the other hand, form stiff films that tend to become fragile, especially if stored for long periods. Film stiffness could also lead to microcapsule fracture and rupture during blending. Table 5.3. Effect of glycerol on microstructural parameters determined by image analysis. (Adapted from Litwinenko et al., 2004, with permission from the publisher.) Crystallization temperature (C)

Glycerol (%)

Mean particle size (µm2)

Number of particles (N)

Following storage for 24 h at 5°C

0.00 0.03 0.10 0.25

40 30 86 69

4845 4630 3300 3646

Following storage for 15 min at 5°C

0.00 0.03 0.10 0.25

163 302 326 150

1386 685 679 1555



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Mechanical Strength Good mechanical properties are critical for processing intact microcapsules without fracture. Edible fats have inherently poor mechanical strength. The latter can be enhanced by incorporating waxes, by modifying their hydrophobic character (Narine and Marangoni, 1999), or by addition of polar substances such as hydrocolloids (Chen and Nussinovitch, 2000). Surface Morphology Smooth surfaces that are free of cracks or crevices are ideal for formulating bakery products with microencapsulated actives and for controlling their release, that is, by retarding microcapsule leaking and premature release. Particle Size Distribution Uniform particle size distribution is critical for many applications, especially in situations where only a very narrow melting window is available. Very large microparticles or microcapsules can cause localized effects such as failure to distribute evenly and eventually form immobile melted masses of barrier material. Very small particles, on the other hand, will have a large surface area which speeds up melting of the coating material upon baking the product. Film Thickness In encapsulation and film coating, one critical decision to be made is how much coating is necessary to achieve desired properties in the finished product. Applied films should be thick enough to overcome surface imperfections but not to modify the release behavior of the microcapsule. For stable dough and batter systems, coatings in the range of 50–95% are common. It should be noted that high film thickness can modify the release of actives in an unpredictable manner and at extreme levels, the release rate tends to become dependent on the size of the core, regardless of the film thickness. Melting Properties Choice of suitable melting properties of the coating material should take into consideration the bakery product’s desired storage and processing conditions. Figure 5.6 shows a typical temperature/time profile of baked batter in a conventional oven. An ideal leavening microcapsule for this application should have a melting profile that closely mirrors that of the baked product. Melting of the shell material should commence as the product temperature approaches or attains 200ºF (93ºC) and should be completed around the first 13–14 min of the baking cycle, that is, before the baked product structure is fully set.

Miscellaneous Examples of Encapsulation and Controlled Release in Bakery Applications Yeasts Yeasts used in baking applications include mainly Saccharomyces cerevisiae, Saccharomyces rosei, Saccharomyces exiguous, and Candida milleri. In the absence of oxygen,

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Batter temperature (°F)

126

Muffin temperature development

250 200 150 100 50 0 1 3

5 7 9 11 13 15 17 19 21 23 25 Time in oven (min)

Figure 5.6.

Temperature development of baked muffin over time.

yeast cells metabolize carbohydrates, via multiple intermediate steps, to produce alcohol, energy, and carbon dioxide gas (Equation 1). The latter is essential for building volume and cell structure in the baked product. Yeast activity takes place during dough preparation and can sharply increase as temperature rises upon preparation and baking (rate doubles for every 10°C rise in temperature). Yeast fermentation C6H12O6 → 2C2H5OH 2CO2 234 kJ

(1)

Baker’s yeast is available in many forms: active dry yeast (ADY), inactive dry yeast, compressed yeast, cream yeast, crumbled yeast, and protected dry yeast (Fleischmann’s, 2001). Although active dry yeast (ADY) has a relatively low moisture content (7.3–8.3%), it is sensitive to oxygen and is always distributed in hermetically sealed pouches under vacuum or flushed with liquid nitrogen. Cream yeast and compressed yeast are usually stored at subfreezing temperatures to maintain their activities. However, problems arise if any of these yeast forms is incorporated into a dough system before freezing because of uncontrolled fermentation and dough expansion (Reed and Nagodawithana, 1991). Many attempts to improve the keeping qualities of Baker’s yeast have been documented (Pelletier and Roger, 1989). Addition of hydrophilic agents (starch, locust bean gum) to yeast preparations to bind up water and potentially retard endogenous metabolic processes has not proven to be very effective. Other technical approaches involve immobilization in chemically cross-linked chitosan beads or activated carriers (Donova et al., 1993; Markvicheva et al., 1991; Freeman and Dror, 1994; Shimon et al., 1991). Luca et al. (1979)) patented a process for treating fresh yeast with hydrophobic silicon dioxide (0.2–1%) to form a colloidal dispersion that was claimed to help maintain the yeast stable at high moisture contents. Soltis and Sell (1998) developed a method for encapsulating Baker’s (cream) yeast and forming a shelf-stable product that can be safely stored at ambient conditions, thus eliminating the need for costly refrigerated storage. Their method consists essentially of pre-adsorbing the high moisture cream yeast onto food fiber, such as grain or bean hulls, followed by coating with a thermoplastic hydrophobic material. The system was claimed to provide a means for delaying the release of active yeast cells until later in the baking process. Newly developed forms of ADY (high ADY) possess high fermentative power and are instantized to allow their incorporation into dough systems without rehydration. However,



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this process results in porous granules that may expose the yeast to undesirable conditions, resulting in their inactivation within three days. Percel (1988) devised a method for preserving the viability of instant yeast via coating (15–40% w/w) with polyethylene glycol of different molecular weights (Carbowax 3350, 4600 and 8000) under mild temperatures of 54–63°C using fluid bed coating. These experiments showed that Carbowax 4600 provided most immediate release of the yeast in cold water while Carbowax 8000 resulted in yeast micropartculates with most abrasion resistance and stability (several weeks in dry mixes compared to few days for the unencapsulated yeast). Fuglsang et al. (2002) used liposome systems to entrap yeast and inhibit their release at ambient temperature. Upon heating from 25 to 60°C, the lipid undergoes phase change, thus releasing the encapsulated yeast material. Chemical Leaveners Manufacturing consistent quality bakery products, especially in large volume operations, relies on using chemical leaveners such as baking powders for cakes, muffins, and cookies and to replace yeasts in bread and dough formulations. Chemical leavening agents operate differently from yeast; while yeast requires sitting time after thawing and prior to baking to produce carbon dioxide, a chemical leavening system produces CO2 gas during baking to expand the dough and create cellular microstructure. Chemical leavening agents comprise a long list of acids and alkalis that vary in their reactivity, stability, solubility, as well as other attributes. (Church and Dwight, 1999). Leavening systems comprise two main components, leavening acid such as sodium acid pyrophosphate (SAP) and base pair such as sodium bicarbonate (soda) that when allowed to react in an aqueous medium (in some cases in the presence of heat) results in the formation of CO2. In such systems, the bicarbonate will provide the gas while the acid will control the reaction rate. Common leavening agents are classified into three categories: (1) slow acting, (2) fast acting, and (3) double acting. Sodium aluminum sulfate (SAS) and monocalcium phosphate monohydrate (MCP) form a double-acting system. Slow-acting systems include a combination of soda and SAP, where baking temperatures affect CO2 release. In fast-acting systems (soda and MCP), CO2 evolution and its release occur effectively during mixing and standing. Deciding which component of the leavening system to encapsulate will depend greatly, among other aspects, on whether the product is a dry mix, bread dough, or a high water activity batter. In high water activity formulations, encapsulating the soda component is more feasible since the acid component can help provide additional antimicrobial protection to the batters. Chemical leavening agents are sensitive to moisture but much less to storage and preparation temperatures; therefore, encapsulating chemical leaveners in a hydrogel system, for example, would not be an option owing to the risk of dissolving the active prior to its point of application. Hydrophobic coatings such as fats and waxes constitute the most commercially viable encapsulating media. Upon heating, the shell melts, thus allowing the leavening active to become available and ultimately to release CO2 needed for building volume and cell structure of the baked product. The rate of capsule melting and CO2 evolution are critical parameter for determining volume, density, and textural qualities of the baked product. This step must occur within narrow limits for some applications such as in the preparation of canned doughs. Manipulating the release rate can be achieved by choosing suitable fats and/or waxes with adequate melting temperatures as well as melting profile, coat thickness, encapsulation technology, and release mechanism (reservoir vs. matrix vs. combination).

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For most bakery systems, encapsulating chemical leaveners via particle coating requires the application of fairly high levels of coating materials onto the crystalline core; ideal coat:core ratios range from 50:50 to 95:5 to ensure complete coverage of the active’s surface. Canned self-sealing doughs represent an exceptional application, where the presence of small amounts of partially-coated or uncoated leavening is desirable. In such situations, the partially-coated or uncoated agents react to form CO2 during or immediately following packaging of the can, thus purging out air and providing a seal from inside the package. The fully-coated portion of the leavening microcapsules is preserved for further reaction during baking. Care should be taken not to allow excessive evolution of CO2 and over-expansion of the pressurized dough. Huang et al (1989) cited an interesting advantage of encapsulating leaveners for microwave baked products i.e. their ionic interactions with the dough components and the subsequent positive impact on reducing gluten toughness and starch firmness, important attributes to forming stable matrix for stabilizing generated CO2. Assessing the stability of encapsulated sodium bicarbonate is achieved by tracking the release of carbon dioxide in sealed packages or containers as well as changes in pH, appearance, and other sensory attributes of the stored product. Figure 5.7 shows a comparison of the risograph gas evolution in refrigerated doughs made using two commercially encapsulated soda products and one unencapsulated control, with E-soda 1 displaying highest stability (lowest CO2 release during storage) while unencapsulated soda showing the least stability (Domingues et al., 2003). Pacifico (2003) suggested that leach rate upon baking (rate at which an encapsulated agent seeps out from the capsule) can be a useful indicator of the functionality of encapsulated leaveners. Accordingly, high leach rate of congealed and coated actives may enhance their reactivity and does not necessarily imply ineffective encapsulation. Several other publications and inventions have surfaced in the last decade claiming ingredients and methods for manufacturing chemically-leavened shelf stable bakery

60

free CO2

50 40 CO2 (%)

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E2-Soda

30 20

E1-Soda

10 0 0

200

400

600

800

1000

1200

1400

Time Figure 5.7. Release of carbon dioxide from refrigerated dough package made with unencapsulated and two encapsulated soda samples (E1-soda and E2-soda) and stored at 45°F for six weeks. (Reproduced from Domingues, 2003.)



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products (Book et al., 2000; Chung and Lavault, 1995; El-Afandi and Citti, 2006; Kringelum et al., 1999; LaBell, 1999; Dorko and Penfield, 1993; Redding, 1995; Redding and Bruce, 2002; Tuazon and Foster, 1992; Wu et al., 2000); each of these inventions is directed to a specific bakery application. Dough Conditioners Bread staling and loss of freshness are major economical hurdles for the baking industry. Several underlying mechanisms have been speculated, with the amylose molecular rearrangements theory being the most plausible. During baking, starch is gradually transitioned from an amorphous structure to a partially crystalline state, a result of inter- or intramolecular interactions via H-bonding of the amylose and amylopectin fractions. Upon recrystallization (retrogradation), starch releases water and the crumb becomes very firm and stale. Storing baked products at room temperature or under high (safe) relative humidity can delay staling, but only for few hours. Emulsifiers are commonly used to help retard staling, though not very effectively; their mechanism of action is believed to be via softening the bread and reducing its firmness rather than retarding starch retrogradation. Amylases that modify starch responsible for staling can be used effectively for increasing shelf life of bread via hydrolysis of the glycosidic linkages in polyglucans. Most commonly used α-amylases are derived mainly from Aspergillus oryzae, Bacillus subtilis, and Bacillus stearothermophilus. These enzymes act on damaged starch particles, thus lowering dough viscosity and producing fermentable sugars necessary for larger bread volume and softer loaves. The Bacillus-derived amylases, however, are fairly heat stable and therefore do not get inactivated during baking, resulting in excessive breakdown of starch and the formation of very moist and sticky crumbs that are difficult to control. Encapsulating these amylases, therefore, can help control their enzymatic activity and reduce their damaging effect on starch. Encapsulating amylases in lipid films has been suggested for their sustained release during baking and shelf life of the baked product (Cole, 1983; Horn, 2002; Schuster et al. 2001; Mori et al., 2002). To ensure even distribution of dough ingredients, manufacturers may sometimes extend the time of mixing. In certain formulations, this overmixing can result in doughs beyond their peak viscosity, thus adversely affecting their viscoelastic properties. Fuglsang et al. (2002) developed a process for encapsulating xylanase enzymes (dough strengtheners) into micelles to help reduce dough stickiness and improve its handling and machinability. Release of the enzyme was designed to be initiated by melting the coating material during leavening or early baking where enzyme activity is desired. Pan breads and flat breads are the most common target applications. Antimicrobial Agents A wide range of antimicrobial agents has been used traditionally for controlling microbial growth in shelf-stable bakery products such as sorbates, benzoates, propionates, paraben, nisin, fumaric acid, and in some cases food grade metabolites produced by Propionibacterium sp. However, effective concentrations of these substances can dramatically affect the flavor, color, odor, and textural attributes of bakery products. Another drawback of using antimicrobial agents is their negative impact on viability of yeasts and enzymes used in bakery systems. Acidic antimicrobial agents, sorbates in particular, can also disturb the

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chemical-leavening balance of doughs and batters. Their reducing power can lead to irreversible changes in the rheological properties of dough and batter systems. An alternate approach for retarding microbial growth of doughs and batters is via pH adjustment (reducing pH depending on type of bacteria and product storage conditions). Although reducing pH can inhibit growth of bacteria and other microorganisms, it has no effect on growth of fungus. Generally, a pH of 5 is acceptable for refrigerated doughs, whereas ambient shelf-stable products require a lower pH (<4). The latter can have an unfavorable reducing effect on the rheological properties of the dough or batter systems. Natamycin is an extremely effective natural antifungal polyene macrolide that can be produced by fermentation of the bacterium Streptomyces natalensis. However, its activity can be negatively affected by extreme pH conditions and in the presence of metals. In addition, natamycin is very antagonistic to yeasts and moulds. Several encapsulation and controlled release formulations have been documented in the patent literature for mitigating these undesirable effects (Kringleum, 1999; Thomas et al., 2005) mainly via coating the preservative with a food-grade high-melting hydrophobic substance and its further dispersion into bread dough system. Methods for encapsulating natamycin using a variety of matrices via extrusion, liposomes, coacervation have been developed (Thomas et al., 2005) and claimed sustained release of the antifungal agent into yeast-leavened dough with no adverse effects on the yeast. Koontz and Marcy (2003) reported successful entrapment of natamycin into a γ-cyclodextrin molecule and formation of stable natamycin/γ-cyclodextrin inclusion complex, despite the incomplete lodging of the bulky natamycin in the γ-cyclodextrin host. Flavors Encapsulation of flavors has been used in baking applications to retard flavor losses during baking and/or eliminate their undesirable interactions with dough components. One group of flavors including cinnamon, cloves, allspice, and nutmeg is known to have negative effect on yeast-leavened doughs, resulting in deteriorating the yeast’s rising properties as well as overall quality of the final baked product. The S-containing major components of cinnamon oil can also have a negative impact on gluten development due to their interactions with disulfide moieties of gluten. Black et al. (1988), developed an encapsulation composition that is claimed to allow incorporation of cinnamon flavor to baked products and to retard the associated undesirable interactions. Wampler (1995) patented a coacervationbased flavor composition to deliver a high payload (70–95% flavor oil). via a cross-linked gelatin shell. The composition was claimed to be stable during mixing with other dough ingredients and subsequent baking. Sweeteners Conklin et al. (1987) developed a microencapsulated particulate sweetening system that is thermally stable and is suitable for bakery applications. The composition is essentially a water-swellable structure containing aspartame/acid core. Co-packing the food acid with aspartame can create adequate pH (<5) conditions in the aspartame’s microenvironment, thus stabilizing the dipeptide. The composition was claimed to be made very compact to reduce wetting via capillary and can also be coated with a hydrophobic substance to delay but not block the diffusion of water.



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Further Remarks • Generally speaking, encapsulation of leavening agents, especially chemical leaveners, requires applications of higher levels of coating than most traditional applications (up to 95% coating may be required). • Reproducibility of production-scale microcapsules is often an issue, especially for moisture-labile actives such as sodium bicarbonate. Regardless of the technology or materials used, leaky capsules may still be generated. Severity of this problem varies with the end-product application. • Manufacturers should be aware of potential differences in performance of encapsulated ingredients in conventional baking compared to microwave baking. • Judging the stability of an encapsulated leavening system should be done by monitoring changes in CO2 generated as well as pH of the dough/cake batter. The latter can be most accurately be determined few hours after preparing the dough or batter. • Incorporating additional amounts of leavening acid into the formula (slightly higher than needed during baking) may help make up for any initial neutralizing reaction that might have occurred upon mixing the batter. • For shelf-stable doughs or batters packaged in containers, injection of an inert gas such as nitrous oxide that is partially soluble in the dough can help produce extra amounts of gas bubbles to compensate for any build up of viscosity and density of batters. The latter may result from reactions with the protein and starch components of the dough/batter system. • Chemical reactivity of leavening systems does not necessarily stop in dry mixes. Condensation reactions can be a problem even at very low moisture levels, which can accelerate other reactions. The role of water in low moisture systems can be more challenging. • The choice of a technology and/or material(s) for encapsulating actives for bakery applications depends on a host of factors such as type of finished product, desired packaging and shelf life, release trigger, site, rate of release, cost and so on. For successful microcapsule design, it is imperative to determine whether the active is sensitive to moisture, water vapor, oxygen, high temperatures, pH, or other environmental parameters.

References Avner, R. and Blatt, Y. 1990. Microcapsules containing food additives and their use. EP 411,326 A2. Azvedo, L.F. and Teixeira, A.M. 2002. A critical review of the modeling of wax deposition mechanisms. Presented at the AIChE 2002 Spring National Meeting, New Orleans, LA, 10–14 March, 2002. Bailey, A.E. 1952. Melting and Solidification of Fats. New York, Interscience Publishers. Bennett, H. 1975. Industrial Waxes. Chemical Publ. Co., New York, NY. Black, M., Popplewell, L.M. and Porzio, M. 1988. Controlled release encapsulation composition. US Patent 5,756,136. Book, S., Corliss, G. and Heidolph, B. 2000. Process and formulation for a chemically leavened dough or bakery product. US Patent 6,149,960. 21 CFR, Code of Federal Regulations(§.184.1973; § 184.1978 and §184.1976). Chen, S. and Nussinovitch, A. 2000. Permeability & roughness determinations of wax-hydrocolloid coatings & their limitations in determining citrus fruit overall quality. Food Hydrocolloids 15: 127–137. Chung, F.H.Y. and Lavault, S., M.-P. 1995. Novel encapsulated leavening acid composition. EP 0,699,392 A2. Church and Dwight Co, Inc.1999. Leavening Sales brochure. Cole, M. 1983. Antistaling baking composition. US Patent 4,416,903.

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Conklin, J.R., Gressgott, H.L. and Wolford, T.D. 1987. Thermally stable particulate artificial sweeteners. EP 0,229,730 A2. Das, S.K. and Gupta, B.K. 1988. Optimization of controlled drug release through micropellitization. Drug Dev. Ind. Pharm. 14(12): 1673–1697. Deasey, P.B. 1984. In Microencapsulation and Related Drug Processes (P.B. Deasy, Ed.), Marcel Dekker, New York, p. 181. Domingues, D.J. 2003. Chemical leavened doughs and related methods. WO 03/020,044 A1. Donova, M.V., Kuz’kina, I.F., Arinbasarova, A.Y., Pashkin, I.I., Markvicheva, E.A., Baklashova, T.G., Sukhodoiskaya, G.V., Pokina, V.V., Kirsh, Y.E., Koshcheyenko, K.A. and Zubov, V.P. 1993. poly-N-vinylcaprolactam gel: a novel matrix for entrapment of microorganisms. Biotechnol. Tech. 7(6): 415-422. Dorko, C.L. and Penfield, M.P. 1993. Melt point of encapsulated sodium bicarbonates: effect on refrigerated batter and muffins baked in conventional and microwave ovens. J. Food Sci. 58(3):574–578. El-Afandi, A. and Citti, J. 2006. Refrigerated dough and product in low pressure container. US Patent 2006/0,177,558 A1. Eldem, P., Speiser, P. and Hincal, A.A. 1991. Optimization of spray-dried and –congealed lipid micropellets and characterization of their surface morphology by scanning electron microscopy. Pharm. Res. 8(1): 47–54. Fleischmann’s Yeasts. 2001. Product directory. Freeman, A. and Dror, Y. 1994. immobilization of “disguised” yeast in chemically cross-linked chitosan beads. Biotechnol and Bioeng. 44: 1083-1088. Fuglsang, C., Callisen, T. and Budolfsen, G. 2002. Dough composition comprising a lipid-encapsulated enzyme. WO 02/19,828 A1. Gherbe-Sellassie, I. 1989. In Pharmaceutical Pelletization Technology (I. Gherbe-Sellassie, Ed.), Marcel Dekker, New York, p. i. Gontard, N., Duchez, C., Cuq, J.L. and Guilbert, S. 1994. Edible composite films of wheat gluten and lipids: water vapor permeability and other physical properties. Int. J. Food Sci. Technol. 29: 39–50. Greener, I. and Fennema, O. 1993. Water vapor and oxygen permeability of wax films. JAOCS 70: 867–873. Hagenmaeir, R. and Baker, R. 1991. Reduction in gas exchange of citrus fruit by wax coating. J. Agric. Food Chem. 41: 283–287. Hernandez, E. 1994. Edible Coatings from Lipids & Resins. Chapter 10: 279- in Edible Coatings & Films to improve Food Quality (J. Krochta, E.A. Baldwin and M.O. Nisperos-Carriedo, Eds.). Technomic Publishing Co., Lancaster, Basel., pp. 279–303. Horn, M.C. 2002. Methods and compositions for retarding the staling of baked goods (US 2002/0,058,086 A1). Huang, V.T., Hoseney, R.C., Graf, E., Ghiasi, K., Miller, L.C., Weber, J.L., Gaertner, K.C., Matson, K., Hunstiger, A.M., Rogers, D.E. and Saguy, I. 1989. Starch-based products for microwave cooking or heating. EP 0,617,896 A2. Ichikawa, H., Kaneko, S. and Fukumori, Y. 1996. Coating performance of aqueous composite lattices with N-ispropylacrylamide shell and thermosensitive permeation properties of their microcapsule membrane. Chem. Pharm. Bull. 44(2): 383–391. John, P.M. and Becker, C.H. 1968. Surfactant effects on spray-congealed formulations of sulfaethylthiadiazolewax. J. Pharm. Sci. 57(4): 584–589. Jozwiakowski, M.J., Jones, D.M. and Franz, R.M. 1990. Characterization of a hot-melt fluid bed coating process for fine granules. Pharm. Res. 7(11): 1119–1126. Kamper, S. and Fennema, O. 1984. Water vapor permeability of an edible fatty acid bilayer film. J. Food Sci. 49: 1482–1485. Kester, J.J. and Fennema, O. 1989a. Resistance of lipid films to water vapor transmission. JAOCS 66: 1139–1146. Kester, J.J. and Fennema, O. 1989b. Tempering influence on oxygen and water vapor transmission through a stearyl alcohol film. JAOCS 66: 1154–1157. Koontz, J.L. and Marcy, J.E. 2003. Formation of natamycin:cyclodextrin inclusion complexes and their characterization. J. Agric. Food Chem. 51: 7106–7110. Kringelum, E. 1999. Compositions containing encapsulated food additives and their use. WO 99/08,553. LaBell, F. 1999. Encapsulated acid improves flour tortilla quality. Prepared Foods October: 91. Lehmann, K. and Dreher, D. 1981. Coating tablets and small particles with acrylic resins by fluid bed technology. Int. J. Pharm. Tech. and Prod. Mfr. 2(4): 31–43. Litwinenko, J.W., Singh, A.P. and Marangoni, A.G. 2004. Effects of glycerol and Tween 60 on the crystallization behavior, mechanical properties and microstructure of a plastic fat. Crystal Growth and Design 4(1): 161–168. Luca, S.F., Thommel, J. and Bronn, W.K. (1979). Free-flowing powdered fresh baker’s yeast preparation and method of producing it. US Patent 4,160,040.



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Madan et al. 1974. Microencapsulation of a waxy solid: wall thickness and surface appearance studies. J. of Pharmaceutical Sci. 63(2): 280–284. Markvicheva, E.A., Kuz’kina, Pashkin, I.I., plechko, T.N., Kirsh, Y.E. and Zubov, V.P. 1991. A novel technique for entrapment of hybridome cells in synthetic thermally reversible polymers. Biotechnol. Tech. 5(3): 223-226. McHugh, T.H. and Krochta, J.M. 1994. Milk protein-based edible films and coatings. Food Technol. 48(1): 97–103. Mori, S., Sato, K. and Tanaka, N. 2002. Dough composition and preparation thereof. US Patent 6,355,282 B1. Narine, S.S. and Marangoni, A.G. 1999. Relating structure of fat crystal networks to mechanical properties: a review. Food Research International 32: 227–248. Narine, S. S. and Marangoni, A.G. 2002. Structure and mechanical properties of fat crystal networks. Advances in Food and Nutrition Research 44: 33-145. Pacifico, C.J. 2003. Chemical leavening ingredient. US Patent 2003/0,031,773 A1. Pelletier, R. and Roger, F. 1989. Process for using bakery additives and bakery yeast. WO 89/00,009. Percel, P.J. 1988. Encapsulated yeast. US Patent 4,719,114. Perron, R. and Ollivon, M. 1992. Proptriétés physiques des corps gras. Propriétés générales de la châine hydrocarbonée. (A. Karleskind, Ed.), Manuel Des Corps Gras, Paris: Tec & Doc Lavoisier, 433–442. Redding, B.K. 1995. Method for entrapment of liquids in transformed waxes. US Patent 5,460,756. Redding, B.K. and Bruce, K. 2002. Ready-to-use food product. WO 02/11,544 A1. Reed, G. and Nagodawithana, T.W. (Eds.). 1991. Bakers yeast production, pp. 261–314. In Yeast Technology, 2nd edition. AVI Publishers, New York. Roberts, B.A., Scavone, T. A. and Riedell, S.P. 2000. Beta-stable low-saturate, low trans, all purpose shortening. US Patent 6,033,703. Sato, K. and Kuroda, T. 1987. kinetics of melt crystallization and transformation of tripalmitin polymorphs. J AOCS 64(1): 124–127. Schuster, E., Sprossler, B. and Hofmeister, J. 2001. Process for making baked articles that retain freshness. US Patent 6,254, 903 B1. Scott, M.W., Robinson, M.J., Pauls, J.F. and Lentz, R.J. 1964. Spray congealing: particle size relationships using a centrifugal wheel atomizer. J. Pharm. Sci. 53: 670–675. Shimon, L.M., Kotorman, M. and Sayani, B. 1991. immobilization of yeast alcohol dehdrogenase on a p-benzoquinone-actiavted silicate carrier. Prikladnaya Biokhimiya i Mikrobiologiya 27 (1): 86-90. Soltis, J. and Sell, J.L. 1989. Yeast composition. US Patent 5,70,669. Sward, G.G. 1972. Natural resins. Am. Soc. Test Mat: 77-91. Thomas, L.V., Gouin, S., Tse, K.L. and Hansen, C.B. 2005. Natamycin dosage form, method for preparing same and use thereof. US Patent 2005/0,042,341 A1. Tuazon, M.T. and Foster, L.C. 1992. Souffle mix. EP 0,545,025 B1. Tulloch, A.P. 1970. The composition of beeswax and other waxes secreted by insects. Lipids 5(2): 247-258. Ubbelohde, A.R. 1978. In The molten State of Matter, John Wiley & Sons, Chichester. Vaghefi, F., Lee, J. and Nalamothu, V. 2001. Zero-order release and temperature-controlled microcapsules and process for the preparation thereof. US Patent 2001/0044026 A1. Van de Tempel, M. 1961. Mechanical properties of plastic disperse systems at very small deformations. J. Colloid Sci. 16: 284–296. Vreeker, A., Hoekstra, L.L., deb Boer, D.C. and Agterof, W.G.M. 1992. The fractal nature of fat crystal networks. Colloids and Surfaces 65: 185–189. Wampler, D. 1993. Aqueous liquid flavor oil capsules, method of making and using in foods. EP 0,633,732 B2. Wetzel, C.R. and Bell, L.N. 1998. Chemical stability of encapsulated aspartame in cakes without added sugar. Food Chem. 63(1): 33-37. Wineman, R.D. 1984. Water emulsion fruit and vegetable coatings based on waxes. Eastman Chem. Prod. Publication # F-257A. Wu, C., Creek, J.L., Wang, K., Carlson, R.M., Cheung, S. and Tang, P.J. 2002. Measurement of wax deposition in paraffin solutions. Presented at the AIChE 2002 Spring National Meeting, New Orleans, LA 10–14 March.

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Encapsulation Technologies for Preserving and Controlling the Release of Enzymes and Phytochemicals Xiaoyong Wang, Yan Jiang, and Qingrong Huang

Introduction According to a report from Business Communication, Inc. (http://www.bccresearch.com), the functional food industry in the US was valued at $20.2 billion in 2002 or 4 percent of the total food industry. Driven by both increasing fortification with healthy food ingredients and consumer demand for novel food products, the functional food market is expected to increase at an average growth rate of 13.3 percent, bringing the market value to $37.7 billion by 2007. The development of functional foods with good bioavailability and eating qualities, however, requires methods for protecting these sensitive components from harmful environmental conditions and masking the taste of some of these components. Encapsulation is the technique by which one material or a mixture of materials is coated with or entrapped within another material or system (Green and Scheicher, 1955). Encapsulation can also be used to mask undesirable odors and bitter tastes of food ingredients. The coated material is called active or core material, and the coating material is called shell, wall material, carrier, or encapsulant. Encapsulation technology is well developed and accepted within the pharmaceutical, chemical, cosmetic, and food industries (Augustin et al., 2001; Heinzen, 2002). Many encapsulation techniques have been developed, such as spray drying, spray chilling and cooling, coacervation, fluidized bed coating, liposome entrapment, rotational suspension separation, and extrusion and inclusion complexation (Madene et al., 2006). The widely used wall materials include polysaccharides and proteins, the key components in both natural and processed foods (Tolstoguzov, 1991). Such polymers have critical impact on the structure and stability of food systems through their gelling, thickening, and surface-stabilizing functional properties. Proteins and polysaccharides are usually used in composites, especially when the creation of new products is required. Intrinsic functional properties of individual components and their interactions determine the final structure, texture, and stability of food materials. Understanding such interactions, especially between proteins and polysaccharides, is important not only for manufacturing cost-effective functional ingredients, but also for designing novel foods and for controlling their structural and textural impact on fabricated foods (Sanchez et al., 1997).

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Complex Coacervate-Based Controlled Release Systems One way to create controlled release encapsulation systems is through the use of complex coacervates formed by proteins and polysaccharides. The basic science behind the coacervation process is well developed and understood. Coacervation is divided into “simple” or “complex” processes. The former involves only one macromolecule and may result from the addition of a dehydrating agent that promotes polymer–polymer interactions over polymer–solvent interactions. In the latter case, two or more oppositely charged macromolecules or colloidal species are present to generate phase separation. In solution, polysaccharide and proteins may undergo two types of phase separation at above or below the isoelectric points of proteins: (i) the solid–liquid phase separation called precipitation (Kokufuta et al., 1981); and (ii) the liquid–liquid phase separation called coacervation (Burgess and Carless, 1984). The coacervate is the denser phase that is relatively concentrated in macromolecules and is in equilibrium with the relatively dilute macromolecular liquid phase (Bungenberg, 1949). The general picture for protein/polysaccharide coacervation from previous studies is that protein molecules initially bind to polysaccharide chains to form primary soluble complexes at first critical pH (pHc), and complex coacervate droplets, which ultimately settle at the bottom to generate the dense coacervate phase, are formed at second critical pH (pH). Primary complex formation, initiated at pHc, is viewed as a microscopic transition on the molecular scales, whereas coacervate droplet formation at pH is viewed as a global phase transition. A typical phase diagram of bovine serum albumin (BSA)/-carrageenan mixtures is shown in Figure 6.1. Three regions are observed in the pH titration curve: (i) at pH > 6.2, there is no change in turbidity; (ii) at pH < 6.2, turbidity starts to increase, which is identified as the intercept of the soluble complex (pHc); and (iii) at pH < 4.8, turbidity increases significantly with the decrease of pH, which corresponds to the phase separation point (pH). Because coacervates formed by polysaccharides and oppositely charged proteins are mainly driven by the long-range character of the electrostatic interaction, physicochemical parameters affecting such interactions, such as pH, ionic strength, polysaccharide linear charge density, protein surface charge density, rigidity of the polysaccharide chain, size of the protein,

Figure 6.1. Plot of turbidity versus pH for mixture of bovine serum albumin (BSA) and -carrageenan (10:1 w/w) in 0.1 M NaCl solution.


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and protein/polysaccharide ratio, strongly influence the formation of the complexes (Burgess and Singh, 1993; Hansen et al., 1971; Hugerth and Sundelof, 2001; Xia and Dubin, 1994). Although extensive studies have been focused on the phase boundaries of protein/ polysaccharide coacervation, understanding the structure of protein/polysaccharide coacervates is still quite lacking (Doublier et al., 2000; Turgeon et al., 2003). With the help of confocal scanning laser microscopy, Sanchez et al. (2002) found that the internal structure of -lactoglobulin/gum arabic coacervates was vesicular or sponge-like, exhibiting numerous spherical inclusions of water depending on the initial mixing ratio. Using small-angle X-ray scattering, Weinbreck et al. (2004a) found that whey protein/gum arabic complex coacervates were dense and structured and could be tuned by pH, protein/polysaccharide ratio, and ionic strength. They also studied the viscoelastic properties of whey protein/gum acacia coacervates and verified that whey protein/gum acacia complex coacervates had the highest viscosity at pH = 4.0, which was ascribed to the strongest electrostatic interaction between whey protein and gum acacia (Weinbreck et al., 2004b). Recently, our group has investigated the dynamic rheolgical properties of BSA/-carrageenan complex coacervates. Figure 6.2 shows typical profile of small deformation oscillatory measurements of BSA/-carrageenan complex coacervates at 0.1 M NaCl concentration and 10:1 protein/polysaccharide ratio, with pH = 4.5. The storage modulus (G) was found to be more than two times greater than the loss modulus (G), wherein the two moduli are almost independent of angular frequency () at > 0.5 rad/s. The high value of G when compared to G indicates that BSA/-carrageenan complex coacervates have a highly interconnected gel-like network structure with mainly elastic behavior, which agrees with the rheological properties of simple coacervates like gelatin (Mohanty and Bohidar, 2005). At similar frequencies, sweep measurements for whey protein/gum Arabic coacervates, G was reported to be three to seven times higher than G, an indication of the highly viscous character of whey protein/gum Arabic coacervates (Weinbreck et al., 2004a). Coacervates of BSA with synthetic polyelectrolyte poly(diallyldimethylammonium chloride) also show viscous nature, with G larger than G in the high-frequency range

Figure 6.2. Plot of storage modulus G and loss modulus G versus angular frequency for the coacervates of BSA with -carrageenan (10:1 w/w) in 0.1 M NaCl at pH 4.5 (Lee et al., 2003).

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(Bohidar et al., 2005). Therefore, different viscoelastic properties in different systems reflect the characteristics of protein/polymer pair and thus distinct coacervate structure. Small-angle neutron scattering (SANS) experiments, which were performed at the intense pulsed neutron source at Argonne National Laboratory, Argonne, IL, have been used to illustrate the structure of complex coacervates formed by -lactoglobulin and pectin. The SANS results for -lactoglobulin/pectin coacervates (30:1 w/w) at two different salt concentrations are shown in Figure 6.3(a). All the curves show a peak of shoulder at intermediate scattering vector range, indicating the electrostatic repulsion of proteins bound onto pectin chains. From the maximum of the peaks in the structure factor curves [Figure 6.3(b)], the distance between bound proteins (d) could be determined: d = 7.6 nm at 0.05 M NaCl is found to be smaller than d = 8.7 nm at 0.1 M NaCl. The strong correlation between peak maxima and their position with salt concentration may be an indication of the more heterogenous and less-structured nature of these coacervates at higher salt concentration. The concept behind protein/polysaccharide complex coacervate-based controlled release delivery systems arises from the pH-triggered phase separation of protein/polysaccharide complexes from the initial mixed solutions, and the subsequent deposition of the newly formed coacervate phase surrounding the active ingredients (Gouin, 2004). If needed, the coacervate shell can be cross-linked using an appropriate chemical or enzymatic crosslinker. A large number of protein/polysaccharide complex systems, such as gelatin/gum acacia (Ijichi et al., 1997; Rabiskova and Valaskova, 1998), gelatin/carboxymethylcellulose (Bakker et al., 1999), -lactoglobulin/gum acacia (Schmitt et al., 2000), and guar/dextran (Simonet et al., 2002), have shown good properties for microencapsulation application. Coacervation is typically used in the encapsulation of flavor oils (Soper, 1995), but can also be adapted for the encapsulation of fish oils (Lamprecht et al., 2001), vitamins (Junyaprasert et al., 2001), enzymes (Dubin et al., 1998), and dietary supplements. To improve the appeal of frozen baked foods upon heating, flavor oil was entrapped in complex coacervate microcapsules using gelatin and gum arabic (Yeo et al., 2005). The design criteria of these systems include: (i) the odor should not be released while the food is frozen or, if thawed, before it is cooked; and (ii) the odor should be released upon heating. The rate of homogenization was found to affect the size of oil cores encapsulated within the microcapsules, whereas the polyion concentrations affected the number of core aggregates consisting of a microcapsule. The comparison of homogenization speed between 3000 and (a)

(b)

0.05 M NaCl 0.1 M NaCl

0.05 M NaCl 0.1 M NaCl

100

S (q)

100

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10 1 0.01

0.1

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0.01

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Figure 6.3. Small-angle neutron scattering intensity profiles from -lactoglobulin/pectin coacervates (30:1 w/w) at different salt concentrations: (a) scattering curves; (b) structure factor curves.



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9000 rpm shows that the microcapsules prepared with a lower homogenization speed were less resistant to heating. A possible explanation for this result is that slower homogenization formed microcapsules having single large cores, which may make them more vulnerable to damage than multivesicular microcapsules produced by higher speed homogenization. Microcapsules prepared with higher concentrations of polyions were less resistant to the release conditions. This result may be due to the fact that lower solution concentrations resulted in bigger agglomerates of oil droplets, which were harder to completely break down.

Encapsulation and Controlled Release of Food Enzymes Enzymes are catalytic proteins that are capable of great specificity and reactivity under physiological conditions. Like most proteins, they are highly susceptible to physiological parameters such as pH and heat and to chemicals like denaturation agents. They are commonly encapsulated and immobilized in food processing, biomedical examination, and antibody labeling. However, they are normally contaminated by proteases, which may generate unpredictable or inaccurate results. Most often, these enzymes are obtained from bacteria or other biomaterials, which subsequently complicates their purification and the formation of protease-free enzymes. The existence of protease in enzymes prevents the use of proteins as wall materials for enzyme encapsulation. Recently, we have developed an inexpensive, fast, and convenient method for encapsulating food enzyme (Jiang and Huang, 2004) through the direct formation of complex coacervate with negatively charged polysaccharide such as -carrageenan. -Amylase was used as a model enzyme to form coacervates with -carrageenan to microencapsulate -amylase. The -amylase encapsulation efficiency and free -amylase were defined as: Encapsulation efficiency %

Free enzyme %

Encapsulated enzyme

(1)

Total enzyme

Non-encapsulated enzyme

(2)

Total enzyme

Our results show that a -carrageenan to -amylase ratio of 1 to 2 resulted in very high encapsulation efficiency (>99 percent) of -amylase as shown in Figure 6.4. -Amylase released from coacervates also maintained the same catalytic activity as the enzyme control, while unencapsulated -amylase lost most of its enzymatic activities after exposure to low pH (i.e., 3) for half an hour. Enzyme kinetics, therefore, can be described by Michaelis–Menten equation, K 1 1 1 m

V Vmax [ S ] Vmax

(3)

Here Km is the Michaelis–Menten constant and Vmax is the maximum hydrolysis rate. Km and Vmax were determined from equation (3). Table 6.1 shows that for coacervate-encapsulated -amylase, even after being treated with acid, -amylase displayed negligible change in enzymatic activities after being released. However, -amylase without coacervate protection almost lost its enzymatic activities, as evidenced by significantly lower values of Km and Vmax.

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Figure 6.4. Encapsulation efficiency curve. Encapsulation has the highest efficiency of about 99.3 percent at the ratio of -carrageenan/ -amylase 1:2 in 0.01 M NaCl.

Table 6.1.

1 2 3

Enzymatic kinetics of -amylase with different treatments Enzyme

Km (g)

Vmax (g/min)

Untreated enzyme (control) Encapsulated, acid treated, released Unencapsulated, acid treated

1.08 1.07 0.04

0.3 0.28 0.0036

These results suggest that the enzyme encapsulation through complex coacervation is an efficient method to protect the enzyme from denaturation.

Encapsulation and Controlled Release of Phytochemicals Phytochemicals have received much attention in recent years from the scientific community, consumers, and food manufacturers due to their potential in lowering blood pressure, reducing cancer risk factors, regulating digestive tract activity, strengthening immune systems, regulating growth, controlling blood sugar concentration, lowering cholesterol levels and serving as antioxidants. The scientific evidence supporting these health-promoting claims of phytochemicals is growing steadily (Wildman, 2001). Although the use of phytochemicals in capsules and tablets is abundant, their effect is frequently diminished or even lost due to their lack of solubility in water, vegetable oils or other food-grade solvents. In addition, insufficient gastric residence time, low permeability and solubility within the gut, as well as instability under conditions encountered in product processing (temperature, oxygen, light) or in the gastro-intestinal tract (pH, enzymes, presence of other nutrients) limit the activity and potential health benefits of phytochemical molecules (Bell, 2001). The delivery of these molecules will therefore require availability of protective mechanisms that can maintain the active molecular form until the time of consumption and to deliver this form to the physiological target within the organism.



Figure 6.5. storage.

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Color changes of epigallocatechin gallate (EGCG) at different pHs after 1-day

To overcome instability, poor water solubility and bioavailability of phytochemicals, encapsulation techniques have been employed to bring about effective amounts of the intact active component to desired target sites in the body. Ideally, actives such as phytochemicals should be stable and intact under stomach acidic conditions, but readily bioavailable under prevailing alkaline conditions of the small intestines (Ho et al., 1992; Salah et al., 1995; Havsteen, 1983). Tea catechins, one of the typical flavonoid components of green tea, have been shown to possess desirable physiological activities such as antioxidants, anti-AIDS virus, antimutagenic, anti-carcinogenic, probiotic, anti-microbial and anti-inflammatory (Havsteen, 1983; Nakagawa et al., 1999). One of the major challenges with utilizing tea catechins is their poor oral bioavailabilities. Epigallocatechin gallate (EGCG), the most important component of catechins contained in green tea, can readily undergo extensive glucoronidation, sulfation, methylation and ring fission in humans, mice and rats (Yang et al., 2002; Nakagawa et al., 1997; Suganuma et al., 1998; Cauturla et al., 2003). In addition, it can easily undergo oxidation at neutral to alkaline pH, especially at high temperatures. Figure 6.5 demonstrates progressive increase in color intensity (browning) of EGCG solutions with increased pH after only one-day storage. Oxidation of EGCG solutions at different pH levels and temperatures can be accurately monitored by tracing their absorption at wavelength of 290 nm using UV spectroscopy. Upon oxidation of EGCG, its absorption wavelength was found to gradually shift to longer wavelength (317 nm). In our laboratories, we attempted to preserve the stability and bioavailability of tea catechins (EGCG) via complex coacervation in carrageenan/gelatin-A (Jiang and Huang, 2004). The encapsulation efficiency of EGCG in these coacervates was determined by high performance liquid chromatography (HPLC) and found to be as high as 89.4% (Figure 6.6). In vitro release of coacervate encapsulated EGCG was also studied in artificial stomach and intestinal juices at 37ºC for 2 hrs and 4 hrs, respectively. The active (EGCG) did not show any release under acidic stomach conditions (confirmed by UV spectra), but was totally released in the first 15 minutes of incubation in artificial intestinal juice (Figure 6.7).

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12 10 8 mg/ml

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Efficiency 89.44%

6 4 2 0

Encapsulated +Un-encap

Un-encap

Figure 6.6. Encapsulation efficiency of complex coacervate-encapsulated epigallocatechin gallate (EGCG) as determined by high-performance liquid chromatography (HPLC).

Stomach

Small intestine

Figure 6.7.

No catechins were released in 2 hrs.

Within 20 min., all catechins were released.

In vitro release of tea catechins in artificial stomach and intestinal juice.

Encapsulation of Phytochemicals by Nanoemulsions Nanoemulsions are a class of extremely small emulsion droplets that can be transparent or translucent with a bluish coloration (Nakajima, 1997; Solans et al., 2005; SonnevilleAubrun et al., 2004). They are usually available in the range of 50-200 nm. Similar to traditional macro-emulsions, two types of nanoemulsions can be prepared, namely oil-in-water (O/W) and water-in-oil (W/O) nanoemulsions. Although emulsions are thermodynamically unstable systems, nanoemulsions, owing to their characteristic size, may possess high kinetic stability against sedimentation or creaming. Nanoemulsions can be prepared by the



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so-called dispersion or high-energy emulsification methods using high shear stirring, highpressure homogenization and ultrasound generators (Walstra, 1983). Other methods such as condensation or low-energy emulsification and phase inversion temperature could produce nanoemulsion almost spontaneously (Rang & Miller, 1999). Nanoemulsions have been investigated for their ability to transport phytochemicals (Solans et al., 2005). The mechanism takes place via large reduction in gravitational force and Brownian diffusion, thus preventing any creaming or sedimentation, followed by steric stabilization and prevention of droplet flocculation or its coalescence. Nanoemulsions also offer other advantages for encapsulating water-soluble (entrapped in the core) and water insoluble (incorporated at the interface or the oil phase) substances that can be designed for slow release applications (Garti et al., 2003; Shefer and Shefer, 2003). This approach was claimed to enhance bioavailability of oil-soluble or water-soluble phytochemicals. Curcumin, an FDA-approved food additive, is widely used as a preservative and yellow coloring agent for foods, drugs, and cosmetics. Curcumin has also been shown to possess unique anti-inflammatory activity (Reddy et al., 2004; Huang et al., 1988, 1994). However, orally administered curcumin is plagued with low systemic bioavailability (Pan et al., 1999). Recently, we developed o/w nanoemulsion for encapsulating curcumin (Wang and others, unpublished). Figure 6.8 shows photomicrographs of curcumin regular- and nanosized- emulsions with the latter exhibiting unique homogeneous droplet size distribution. Using particle size analysis, average diameter of curcumin nanoemulsion droplets was found to be 65 nm. The mouse ear inflammation model is commonly used to test the bioavailability of anti-inflammatory agents in vivo. In such studies, topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) can rapidly induce edema of mouse ear in a dose- and time-dependent manner. Earlier studies in our laboratory have shown that oral administration of anti-inflammatory agents such as aspirin and garcinol can inhibit TPA-induced edema in mouse ears. We have also reported that various levels of garcinol were found in serum, ear, liver, lung and colon after oral administration of garcinol by female CD-1 mice for several hours. In addition, oral administration of aspirin or garcinol by gavages resulted in marked inhibition of TPA-induced edema in mouse ears. In contrast, oral administration of curcumin, a poor bio-available anti-inflammatory agent, had little or no effect on TPA-induced edema of mouse ears. However, oral administration of two different preparations of curcumin emulsion (10 mg curcumin in 1 ml) prepared by either high speed homogenization (regular) or high pressure homogenization (nanoemulsion) to mice by gavages at 30 min prior to topical application of TPA has markedly inhibited TPA-induced edema of mouse ears by 43 and 85%, respectively.

Bioconjugation of Phytochemicals Nanoparticles are defined as submicronic (<1 μm) colloidal systems made of polymers both biodegradable and non-biodegradable. Nanocapsules, one type of nanoparticles, are vesicular systems in which actives such as flavonoids can be confined to a cavity, generally, an oily or aqueous core surrounded by a unique polymeric membrane. Nanospheres, on the other hand, are matrix systems in which the active is dispersed throughout the particles. Initial research on colloidal carriers was mainly focused on liposomes which are very difficult to produce or stabilize for practical applications. In contrast, nanopraticles owing to their unique stability can potentially be superior carriers compared to liposome.

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(a) Figure 6.8.

(b) Microscope images of curcumin normal emulsions (left) and nanoemulsions (right).

Activities of polyphenols such as their anti-oxidative power, circulation time in the human body and other activities can be reduced upon exposure to environmental stresses such as moisture, heat, and oxidation (Hagerman et al., 1998; Kurisawa et al., 2003). We have attempted to preserve polyphenol activities, in particular their anti-oxidative ability by means of synthesizing poly(catechin)via enzyme-catalyzed oxidative coupling using horseradish peroxidase as a catalyst (Shin and Huang, unpublished results). The poly-catechin showed great improvement in antioxidative activity such as radical scavenging activity against the superoxide anion and inhibition effects against free radical induced oxidation of low-density lipoprotein, compared to the catechin monomer. In addition, poly-(catechin) showed very high inhibition effects on xanthine oxidase activity, whereas the catechin monomer showed very low inhibition effects.

Conclusion One of the most important stakes in the health promotion industry is the efficient encapsulation of highly valuable phytochemicals. Taking advantage of nanoscale particles, nanoemulsions and nanoparticles, provide excellent vehicles for encapsulating phytochemicals and to preserve their stability and bioavailability. Another unique encapsulation technique for such applications is complex coacervation. Numerous protein/polysaccharide pairs have been demonstrated to provide controlled-release of phytochemicals in vitro as well as in vivo. Conjugation of phytochemicals can also play a promising role in encapsulating large-scale actives and in their effective utilization in food systems. Indeed, the choice of an appropriate technique, however, depends on the properties of the active compounds, the degree of stability required during storage and processing, desired release properties, maximum obtainable phytochemical load as well as production cost.

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Lamprecht, A., Schafer, U., Lehr, C. M. 2001. Influences of process parameters on preparation of microparticle used as a carrier system for W-3 unsaturated fatty acid ethyl esters used in supplementary nutrition. J. Microencapsul., 18, 347–357. Lee, J. Y., Ruengruglikit, C., Huang, Q. R. 2003. Interactions between Carrageenan and BSA: (1) Effects of linear charge density and ionic strength. Polym Prepr., 44, 289–290. Madene, A., Jacquot, M., Scher, J., Desobry, S. 2006. Flavour encapsulation and controlled release. Int. J. Food Sci. Technol., 41, 1–21. Mohanty, B., Bohidar, H. B. 2005. Microscopic structure of gelatin coacervates. Int. J. Biol. Macromol., 36, 39–46. Nakagawa, K., Miyazawa, T. 1997. Absorption and distribution of tea catechin, (-)-epigallocatechin-3-gallate, in the rat. Nutr. Sci. Vitaminol., 43, 679–684. Nakagawa, K., Ninomiya, M., Okubo, T., Aoi, N., Juneja, L. R., Kim, M., Yamanaka, K., Miyazawa, T. 1999. Tea catechin supplementation increases antioxidant capacity and prevents phospholipid hydroperoxidation in plasma of human. J. Agric. Food Chem., 47, 3967–3973. Nakajima, N. 1997. Microemulsions in cosmetics. In: Solans, C., Kunieda, H. (Eds.), Industrial Applications of Microemulsions (pp. 175–197). New York: Marcel Dekker. Pan, M. H., Huang, T. M., Lin, J. K. 1999. Biotransformation of curcumin through reduction and glucuronidation in mice. Drug Metab. Dispos., 27, 486–494. Rabiskova, M., Valaskova, J. 1998. The influence of HLB on the encapsulation of oils by complex coacervation. J. Microencapsul., 15, 747–751. Rang, M. J., Miller, C. A. 1999. Spontaneous emulsification of oils containing hydrocarbon, nonionic surfactant, and oleyl alcohol. J. Colloid Interface Sci., 209, 179–192. Reddy, R. S., Rao, C. V. 2004. Chemoprevention of colon cancer by curcumin. In: Meskin, M. S., Bidlack, W. R., Davies, A. J., Lewis, D. S., Randolph, R. K. (Eds.), Phytochemicals: Mechanisms of Action (pp. 177–192). Boca Raton, FL: CRC Press. Salah, N., Miller, N. J., Paganga, G. 1995. Polyphenolic flavanols as scavengers of aqueous phase radicals and as chain breaking antioxidants. Arch. Biochem. Biophys., 322, 339–346. Sanchez, C., Schmitt, C., Babak, V. G., Hardy, J. 1997. Rheology of whey protein isolate-xanthan mixed solutions and gels. Effect of pH and xanthan concentration. Nahrung, 41(6), 336–343. Sanchez, C., Mekhloufi, G., Schmitt, C., Renard, D., Robert, P., Lehr, C.-M., Lamprecht, A., Hardy, J. 2002. Selfassembly of -lactoglobulin and acacia gum in aqueous solvent: structure and phase-ordering kinetics. Langmuir, 18, 10323–10333. Schmitt, C., Sanchez, C., Despond, S., Renard, D., Thomas, F., Hardy, J. 2000. Effect of protein aggregates on the complex coacervation between beta-lactoglobulin and acacia gum at pH 4.2. Food Hydrocolloids, 14, 403–413. Soper, J. C. 1995. Utilization of coacervated flavors. ACS-Symposium Series, No. 590, 104–112. Shefer, A., Shefer, S. 2003. Multicomponent Controlled Release System for Oral Care, Food Products, Nutracetical, and Beverages. US20030152629. Simonet, F., Garnier, C., Doublier, J. L. 2002. Description of the thermodynamic incompatibility of the guardextran aqueous two-phase system by light scattering. Carbohydr. Polym., 47, 313–321. Solans, C., Izquierdo, P., Nolla, J., Azemar, N., Garcia-Celma, M. J. 2005. Self-assembly of surfactants and phospholipids at interfaces between aqueous phases and thermotropic liquid crystals. Curr. Opin. Colloid Interface Sci., 10, 102–110. Sonneville-Aubrun, O., Simonnet, J. T., L’Alloret, F. 2004. Nanoemulsions a new vehicle for skincare products. Adv. Colloid Interface Sci., 108–109, 145–149. Suganuma, M., Okabe, S., Oniyama, M., Tada, Y., Ito, H., Fujiki, H. 1998. Wide distribution of [3H](-)epigallocatechin gallate, a cancer preventive tea polyphenol, in mouse tissue, Carcinogenesis, 19, 1771–1776. Tolstoguzov, V. B.1991. Functional properties of food proteins and role of protein–polysaccharide interaction. Food Hydrocolloids, 4, 429–468. Turgeon, S. L., Beaulieu, M., Schmitt, C., Sanchez, C. 2003. Protein–polysaccharide interactions: phase-ordering kinetics, thermodynamic and structural aspects. Curr. Opin. Colloid Interface Sci., 8, 401–414. Weinbreck, F., Tromp, R. H., de Kruif, C. G. 2004a. Composition and structure of whey protein/gum arabic coacervates. Biomacromolecules, 5, 1437–1445. Weinbreck, F., Wientjes, R. H. W., Nieuwenhuijse, H., Robijn, G. W., de Kruif, C. G. 2004b. Rheological properties of whey protein/gum arabic coacervates. J. Rheol., 48, 1215. Wildman, R. E. C. 2001. In: Wildman, R. E. C. (Ed.), Handbook of Nutraceuticals and Functional Foods. New York: CRC Press.



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Microencapsulation of Flavors by Complex Coacervation Curt Thies

Introduction The encapsulation of flavors was first reported in the 1930s when it was observed that a volatile substance, isopropanol, was retained by a spray-dried particle (Thies, 1999). This observation catalyzed the development of spray dry flavor encapsulation, a technology responsible today for the daily production of tons of encapsulated flavor products globally. Reineccius (2004) and others (Brenner, 1983; Re, 1998; Liu et al., 2001) have discussed spray dry encapsulation technology in some detail. Although spray drying is currently the dominant flavor encapsulation technique, a number of alternate encapsulation technologies exist and offer a potential means of producing unique flavor-loaded microcapsules. Complex coacervation encapsulation procedures fall into this category. Accordingly, this contribution is a discussion of various aspects of complex coacervation encapsulation technology and the encapsulation of flavors for food products. Only complex coacervation processes based on food-grade polymers are considered here. Although fragrances are not considered in this contribution, much of the discussion is also applicable to the encapsulation of fragrances as well as other complex core materials.

Flavor Encapsulation The preparation of flavor-loaded microcapsules is a complex task. It is much more complicated than it appears at first glance, because flavor microcapsules must meet a series of requirements. One requirement is the production of microcapsules that retain the desired properties of the flavor encapsulated. Each flavor is a unique and complex mixture of many compounds. These compounds have a broad range of structures with vapor pressures, solvent solubility, and stability that differ significantly. Any useful encapsulation technology must be able to accommodate this variability. Ideally, the chemical composition of the flavor is unchanged by the encapsulation process, and the encapsulated flavor is identical in all respects to the unencapsulated flavor. In reality, this is generally not the case. Encapsulation processes typically change the chemical composition of a flavor in some way. Loss of more volatile or more water-soluble components during an encapsulation process is common. Such losses can have a significant effect on the desired olfactory properties of the flavor. Flavor-loaded microcapsules must contain enough active agents to cause the desired effect. The amount of flavor required varies with the nature of the flavor and intended food product. Although flavor impact can be altered by varying the flavor loading of a capsule of fixed size as well as by varying capsule size, the degree of variation may be limited by the nature of the food product. For example, capsule size variations may be limited by the need

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to retain structural integrity during processing while having the ability to be ruptured by chewing. Variations in amount of flavor carried by a capsule of fixed size may be limited by the capsule formation process as well as the retention or barrier properties of the capsule shell. Stability of flavor-loaded capsules during processing and storage is an issue that must be addressed. Such capsules must have acceptable stability from the time of formation to consumption of the food product. Stability during processing of capsules as they are incorporated into a food product can be a problem if this involves high shear or a combination of high temperature and shear. Shelf life stability after incorporation and storage in a food product is important as is the ability of capsules to release their contents during food preparation or consumption. This series of stability requirements is imposing and often limits actual capsule performance. Factors that affect capsule stability include oxygen, moisture, heat, and light. In principle, the shell of a capsule should protect an encapsulated flavor from these agents, but deficiencies in either the capsule shell or the material(s) from which the shell is prepared may cause a shell to provide inadequate protection. Shell materials typically used to form food-grade flavor capsules may experience major property changes during food-processing steps that involve heat and moisture. Of course, flavor-loaded microcapsules must meet specifications imposed by governmental regulatory agencies responsible for food safety. This requirement puts a restriction on the shell materials that can be used. It also limits the nature and amount of processing agents used in a capsuleformation process. In summary, the complex series of specifications associated with the formation of flavorloaded microcapsules makes their preparation an interesting field of study. Much can be done in order to produce capsules that more closely approach the degree of perfection desired. Studies by various workers of the diffusion barrier properties of candidate shell materials merit review, because they provide much insight into the properties of such materials and help one develop a realistic appreciation for the limitations of specific shell materials and capsule formation processes (Menting and Hoogstad, 1967; Kerkof and Thijssen, 1974; Thijssen, 1975; Rulkans and Thijssen, 1978; Goubet et al., 1998). Although most of these involve spray drying and freeze drying studies, the results obtained are applicable to capsules formed by any encapsulation process.

Complex Coacervation Before discussing complex coacervation encapsulation processes, it is appropriate to consider the nature of complex coacervate systems and some of their characteristic features. Complex coacervation is the liquid/liquid phase separation that occurs when solutions of two or more oppositely charged polyelectrolytes are mixed under suitable conditions. Two liquid phases are formed: the coacervate phase and the supernatant or equilibrium liquid phase. The coacervate phase is a relatively concentrated polymer solution that participates in a complex coacervation encapsulation system. It is in this phase that capsule shell forms. The supernatant phase is a dilute polymer solution and serves as the continuous phase in which capsule formation occurs. Dilution favors complex coacervation and is a property that distinguishes complex coacervation from other polymer phase-separation phenomena. Complex coacervation is affected by many variables. Bungenberg de Jong’s experimental studies in the 1930s and 1940s provide much useful background data about the phenomenon


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(Bungenberg, 1949). Since then, a variety of workers have considered various aspects of coacervation including theoretical analyses based on polymer solution thermodynamics (Burgess, 1990; Veis, 1970; Schmitt et al., 1998). Although this information provides a guide for developing complex coacervation microencapsulation procedures, it is important to recognize that conditions that optimize the degree of coacervation in a specific system may not be conditions under which useful microcapsules can be formed. For example, these conditions may produce a complex coacervate that is too viscous to yield acceptable capsules.

Selected Properties of Complex Coacervates Many complex coacervation systems suitable for the production of microcapsules exist. In virtually all cases, gelatin is the polycation used. A wide range of polyanions is used. Each system operates under a unique set of conditions and has a unique set of properties once formed. This reflects differences in nature and frequency of ionic groups distributed along the chains of the polymers involved in a specific complex coacervation procedure. Differences in polymer chain structure and molecular weight (MW) are other factors that influence coacervation. One of the polyelectrolytes used in a typical complex coacervation encapsulation procedure is a natural polymer with a complex molecular structure. For example, gelatin polymer molecules are made up of a number of different amino acids with different pendent groups. Because anionic and cationic pendent groups are distributed along the polymer chain, gelatin is a polyampholyte. The cationic groups are primary amino groups, while the anionic groups are carboxyl groups. The degree of ionization of these ionic groups varies with pH, so the net charge carried by a gelatin molecule varies with pH. Gelatins formed by acid hydrolysis of collagen are classified as Type A or acid precursor gelatins. Alkaline hydrolysis yields Type B or alkaline precursor gelatins. The isoelectric point (pI) of Type A gelatins is typically 8–9, while the typical pI of Type B gelatins is 4–5. The reduced pI value of Type B gelatins is caused by hydrolysis of pendant amide groups under alkaline conditions. The number of primary amino groups distributed along a gelatin chain is essentially independent of the hydrolysis procedure. Although both types of gelatins produce complex coacervates suitable for microcapsule formation, Type A gelatins historically have been used most. Significantly, for gelatin to carry a net cationic charge, it must be at a pH lower than its pI. Although gelatin is the polycation involved in the formation of complex coacervates used in microencapsulation processes, many different polyanions are used. They differ greatly in anion group distribution along a polymer chain as well as the nature of this group. This is particularly true of natural polymers that carry an anionic group. Gum arabic (GA) and alginate, two polysaccharides, derive their anionic character from carboxyl groups distributed along their polymer chains. In GA, such groups are located on shortchain branches hanging off the primary polymer chain. Approximately 20% of the sugar units in GA contain a carboxyl group. In contrast, alginate molecules are linear polymer chains and every sugar in the chain has a carboxyl group. The degree of ionization of carboxyl groups is a strong function of pH and steadily decreases as pH decreases. The anionic character of sodium polyphosphate, an inorganic material, is due to the phosphate group. Carrageenan, a polysaccharide with a linear chain, has sulfate groups distributed along its chain. The average number of sulfate groups per sugar unit varies with the type of carrageenan.

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Chapter 7

Because the polymers used to form complex coacervates differ significantly in composition and structure, properties of complex coacervates formed by different polymers differ significantly. In order to illustrate this point, Table 7.1 contains degree of coacervation and enrichment data at 50°C for three gelatin-based complex coacervation systems used to prepare microcapsules: gelatin/gum arabic (GGA), gelatin/polyphosphate (GP), and gelatin/ sodium alginate (GAlg) (Commandur et al., 1989). Degree of coacervation (ρ) is defined as the fraction of total polymer in the system that is in the coacervate (Veis and Aryani, 1960). Enrichment (ε) is defined as the ratio of polymer concentration in the coacervate phase to that in the supernatant phase (Veis and Aryani, 1960). GGA and GP coacervates were formed by interacting 285 bloom Type A gelatin with GA and sodium hexametaphosphate, respectively. GAlg coacervates were formed by interacting 231 bloom Type A gelatin with a hydrolyzed alginate. Each coacervation system was studied at three initial solids concentrations and three pH values in order to illustrate how changes in these variables affect coacervate formation. Table 7.1. Tabulation of degree of coacervation (ρ) and enrichment data (ε) at 50ºC for several coacervation systems Coacervate system GGA

GAlg

GP

Initial solids w/v (%)

pH

Degree of coacervation

Enrichment

3.96 3.3 2.83

4 4 4

0.86 0.88 0.89

22 34.8 47.7

3.96 3.3 2.83

4.2 4.2 4.2

0.78 0.81 0.81

11.3 17 21.2

3.96 3.3 2.83

4.4 4.4 4.4

0.81 0.8 0.83

12.1 16.6 24.2

2.11 1.81 1.59

4 4 4

0.86 0.83 0.82

66.7 68 71.7

2.11 1.81 1.59

4.2 4.2 4.2

0.66 0.73 0.7

25.3 42.5 54.7

2.11 1.81 1.59

4.4 4.4 4.4

0.78 0.81 0.79

35.7 53 54.7

5 4.54 4.17

4 4 4

0.74 0.78 0.78

11.5 15.5 20.9

5 4.54 4.17

4.2 4.2 4.2

0.72 0.71 0.74

9.4 11.3 14.5

5 4.54 4.17

4.4 4.4 4.4

0.61 0.57 0.65

4.8 5.7 10.2



153

Indeed, at sufficiently high concentration and pH values, complex coacervation does not occur. Initial solids content is defined as the total polymer solids in the system at the time when complex coacervation occurred. The data in Table 7.1 were obtained by using initial solids of 1.6–5 w/w% and pH values of 4.0–4.4 pH. Although these initial solids and pH values are typical for many coacervation systems used to make microcapsules, situations exist where suitable coacervates will form when values of one or both parameters fall outside these ranges. The gelatin/polyanion ratio used for forming gelatin-based complex coacervates varies with ionic equivalent weight of the polyanion(s) used. The GGA complex coacervate data in Table 7.1 were formed by using a 1:1 w/w ratio of gelatin and GA, because both polymers have an ionic equivalent weight of roughly 1000. Alginates have an ionic equivalent weight of approximately 180, so the gelatin/alginate the ratio used was 3.7:1 w/w. The w/w gelatin/polyphosphate ratio was 9:1. It is high, because polyphosphates have a low ionic equivalent weight. In all cases, the polyanion ratios reported here are those typically used by the author to produce complex coacervates suitable for microcapsule formation. Complex coacervates will form when a coacervation system contains excess gelatin or polyanion, but it is common practice to use gelatin/polyanion ratios that approach ionic equivalency. Although the data in Table 7.1 are for coacervation systems based on one polyanion, mixtures of several chemically different polyanions can be used to produce gelatin-based coacervates suitable for microcapsule formation. This enables one to develop a broad range of complex coacervate systems suitable for microcapsule formation. The data in Table 7.1 (Commandur et al., 1989) show that ρ and ε at 50°C are affected by the nature of the polyanion involved in coacervate formation, system pH, and initial solids content of the system. For all coacervation systems examined, values of ε at constant pH increase as the initial solids content decreases. This reflects the increase in intensity of coacervation upon solution dilution, a characteristic feature of complex coacervation. In contrast, other polymer phase-separation phenomena such as polymer/polymer incompatibility and salting out (simple) coacervation are favored by increasing the concentration of the molecules involved. Values of ρ for the GGA system fall between 0.8 and 0.9 over the range of initial solids and pH values examined. Thus, in these GGA systems, 80–90 w/v% of the polymers were concentrated in the coacervate phase. The GGA coacervate phases formed are 15–26 vol% of total system volume and have a solids content of 10–14 w/v%. Solids content of the supernatant phase was 0.3–0.9 w/v%. Since values of ε found for the GGA systems range from 11 to 35, a high degree of polymer partitioning was achieved. At constant initial solids, values of ε decrease as pH increases. GP coacervate phases occupy 13–21 vol% of total system volume and have a solids content of 13–21 w/v%. GP ρ values of 0.6–0.8 and ε values of 5–21 are lower than the range of ρ and ε values found for GGA and GAlg systems. Thus, the GP coacervate system achieves a lower degree of polymer partitioning. The solids content of GP supernatant phases range from 1 to 2.3 w/v%, considerably higher than that observed with GGA and GAlg systems. Because gelatin concentrations of approximately 2 w/v% approach the concentration at which gelatin solutions gel, operating conditions of an encapsulation process based on GP must be adjusted to keep the supernatant solids concentration below 2 w/v%. The solids content of a GAlg coacervate phase at 50°C varies from 15 to 22 w/v% while the solids content of a GAlg supernatant phase varies from 0.3 to 0.9 w/v%. The GAlg

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Chapter 7

coacervate is 4–7 vol% of total system volume, considerably lower than the values observed with GGA or GP coacervates. Values of ρ for the GAlg systems are 0.7–0.9, a range similar to but broader than that observed with GGA coacervates. The 25–72 range of ε values for GAlg coacervate systems is higher than that observed with GGA or GP systems. Thus, GAlg coacervate systems more effectively concentrate or partition into the coacervate phase the polymers involved in complex coacervation. At first glance, this is surprising, because the volume of the GAlg coacervate phase is much smaller than that of the GGA and GP coacervate phases, while the solids content of the GAlg coacervate phase is similar to that of the GGA and GP coacervate phases. Closer analysis leads to the recognition that the initial solids content of the GAlg system is measurably lower than that of the GGA and GP systems. Thus, the GAlg coacervate phase contains a higher percentage of polymers present in the GAlg system, even though it occupies a smaller volume fraction than the GGA and GP coacervate phases and has a solids content similar to these systems. The ρ and ε data reported in Table 7.1 provide valuable insight into the nature of three complex coacervate systems, but they reveal nothing about coacervate rheology or the temperature at which the coacervates gel. Coacervate rheology is a primary variable that affects capsule shell formation and capsule aggregation. Accordingly, the viscosity of a number of coacervate phases was measured over a range of temperatures by capillary viscometry (Commandur et al., 1989). Table 7.2 summarizes results of these measurements. The data show that the sodium alginate and GA solutions used to form GGA and GP coacervates have a viscosity of 3–6 cS at 50°C. This viscosity increases as the temperature is reduced to 30°C, but the viscosity increase caused by cooling is not pronounced, because neither polymer alone gels on cooling. In contrast, viscosity of the gelatin solutions examined steadily increases as the solution temperature is reduced from 50°C to 35°C. The viscosity of most such solutions becomes unstable at 32°C. That is, the recorded viscosity steadily increases toward infinity as the time at 32ºC increases. This viscosity increase is due to the onset of gelation. Not shown in Table 7.2 are viscosity data for GGA, GP, and GAlg supernatant phases that exist in equilibrium with the GGA, GP, and GAlg coacervate phases for which viscosity data were obtained. Most supernatant phases have a viscosity below 1 cS at temperatures ranging from 50°C to 35°C and provide no indication that they will gel on further cooling. Exceptions are two GP supernatant solutions isolated from pH 4.4 GP coacervate systems. The viscosity of both solutions remained below 1.5 cS as they were cooled to 35°C, but the upward slope of their temperature–viscosity plots suggests that both will ultimately gel. GGA coacervate viscosity at pH 4.4 and 50°C ranged from 23 to 58 cS, i.e., 2 to 5 times greater than the 11.3 cS viscosity of a 10% solution of 285 bloom Type A gelatin at 50ºC. Viscosity of the GGA coacervates steadily increases as the system is cooled. They either gel or become unstable due to onset of gelation as the temperature falls below 35°C. Decreasing the pH of GGA coacervate formation from 4.4 to 4.0 increases coacervate viscosity at all temperatures examined. The viscosity of GP coacervates at 50°C is 47–373 cS, measurably higher than the viscosity of GGA coacervates. Reducing the pH of a GP coacervate from 4.4 to 4.0 causes a major increase in coacervate viscosity and raises the GP coacervate gelation temperature above 35°C. The viscosity of all GAlg coacervates at 50°C is 20–60 times higher than that of most GGA and GP coacervate phases at 50°C. Although GAlg coacervate phases have a very

b

a

5.2 5.4 5.5 4.2

4.4 4.4 4 4 4.4 4.4 4.2 4 4.4 4.2 4 4

pH 10.4 12.1 13.2 14.3 12.3 14.3 19.8 20.9 15.6 18.4 20 18.6

Solids (w/v%)b

Total system solids at the time of coacervation. Total solids of solution used for capillary viscosity measurement.

Gelatin solution Type A (285 bloom) Gelatin solution Type A (231 bloom) Sodium alginate solution Gum arabic solution

GAlg Coacervate

GAlg Coacervate

GP Coacervate

GP Coacervate

GGA coacervate

3.96 2.83 3.96 2.83 5 4.17 4.55 4.17 2.11 1.59 2.11 1.59 10 15 10 15 2 10

Initial solids (w/v%)a 23 39 39 58 47 67 298 373 679 1245 1391 1382 11.5 31 7.3 15.9 3

50°C 26 42 42 63 56 74 342 402 806 1480 1665 1698 13.2 35 8 17.8 3.4 4.1

45°C 29 47 48 74 98 120 1782 2606 1636 2485 2806 3254 14.8 40 9.2 20.6 3.7 4.5

40°C

221 679 Gelled Gelled 3396 7404 6220 7658 17 52.1 10.3 24.6 4 4.9

35 62 79

37°C

Gelled Gelled Gelled Gelled 20 66.6 11.5 28.9 4.2 5.4

46 96 97 Unstable Gelled Gelled

35°C

Viscosity (cS)

5.5

Unstable Unstable 16.2 Unstable

107 Unstable 143 Gelled

32.5°C

Changes in viscosity of various coacervate systems at different temperatures (from Commandur et al., 1989, with permission)

GGA coacervate

System

Table 7.2.

Gelled Gelled Unstable Gelled 4.8 6.3

Gelled Gelled Gelled

30°C


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Chapter 7

high viscosity at temperatures ranging from 50°C to 40°C, they do not appear to gel until cooled to 35°C. As the data in Table 7.2 show, complex coacervate viscosity is a strong function of the coacervation system, pH, and temperature. Characterizing the effect of temperature changes on rheology of a coacervate system is an important task, because all gelatin-based complex coacervation encapsulation protocols involve a cooling step that lowers the system temperature below the gel temperature of the coacervate. In such processes, complex coacervate formation always occurs above the coacervate melt temperature so that the coacervate formed is initially a liquid. It must have a viscosity that is sufficiently low to enable it to engulf dispersed core material droplets or particles, thereby coating them with a thin film of liquid coacervate. Once a coacervate is formed, the two-phase system is cooled below the gel temperature of the coacervate, thereby setting the gel structure of the coacervate. This transforms the thin liquid film that surrounds the small droplets of core material into a thin gel coating. Viscosity of a coacervate above its melt temperature and changes in its rheology as cooling occurs have a major impact on the success of a complex coacervation encapsulation process. The viscosity data in Table 7.2 cover a very large range of values. Although capillary viscometry is appropriate for measuring the viscosity of Newtonian fluids, it has not been determined that all complex coacervates exhibit Newtonian flow behavior, especially at temperatures that approach the gel point. Leuenberger (1991) reported that 10% w/w% solutions of several different gelatin samples at 40°C are linear in the shear rate range of 10–350 s–1. Deviations from linearity occur at high shear rates. Because of the relative fluidity at 50°C of GGA and GP coacervates, it is believed that they exhibit Newtonian behavior at this temperature. The long capillary flow times of the GA coacervates at 50°C suggest that such coacervates exhibit non-Newtonian flow behavior. Although additional measurements are needed in order to properly characterize the rheological behavior of a range of complex coacervates, the data in Table 7.2 provide a means of comparing the apparent viscosity of several coacervates used to form microcapsules. These data illustrate the significant effect that composition of a complex coacervate has on its rheological properties. This has a profound effect on capsule formation. It is relevant to note that Koh and Tucker (1988a, b) characterized the gelatin– carboxymethylcellulose (CMC) complex coacervate system. They reported characterization data similar to that shown in Tables 7.1 and 7.2 for this system. Although their characterization data as well as that shown in Tables 7.1 and 7.2 shed valuable insight into the specific complex coacervation systems studied, it must be recognized that such data represent typical properties of a given complex coacervate system. Specific ρ and ε values reported for any complex coacervate system can be difficult to precisely reproduce consistently within the same laboratory by the same person, let alone different laboratories and different persons. This problem is caused by the sensitivity of complex coacervation to many factors. Experimental variations can be minimized by establishing standard experimental protocols. For example, all of the data shown in Table 7.1 were obtained by using aqueous solutions polymers from the same lot. Distilled water was the solvent. Very different results would most likely occur if tap water is used, because tap water can contain a variety of salt ions, and salt ions repress complex coacervation. Lot-to-lot variations in properties of either the gelatin or the polyanion used will also affect results obtained. In order to minimize variation in reported results, the polymer solution preparation protocol must be standardized as must the length of solution storage before use.



157

In cases where a flavor is being encapsulated by a process based on complex coacervation, water-miscible or partially water-soluble components present in the flavor can affect the coacervation process and nature of the coacervate formed. Seemingly small variations in a coacervate system can have a major effect on complex coacervation results.

Complex Coacervation Encapsulation Processes Bungenburg de Jong’s studies of the complex coacervation of gelatin and GA formed the basis for the original GGA complex coacervation encapsulation procedure reported by Green and Schleicher (1957). Figure 7.1 is a flow diagram of their process. The first step is to emulsify the material being encapsulated in a warm (40–60°C) aqueous gelatin solution. This material is commonly called the core material. It is typically a water-immiscible oil, but could be a water-insoluble solid. Oil emulsification typically is carried out in a warm 8–11 w/w% gelatin solution because such concentrated solutions increase the ease of emulsification to a desired drop size. The second step is to add GA and dilution water to the system followed by adjustment of the pH to a value at which sufficient complex coacervate phase to encapsulate the dispersed oil droplets is formed. As noted in Table 7.1, this pH typically falls in the range of 4.0–4.4, although higher or lower pH values may be needed for a specific core material. Dilution water is added to the system at this point in order to lower the total polymer solids content from the 8 to 11 w/v% used in the emulsification step to the 2.83–3.96 w/v% at which complex coacervation occurs (see Table 7.1). The third step is to cool the system below the gel point of the coacervate, thereby causing the coacervate to gel. In order to improve capsule shell stability, capsules with shells

Waterimmiscible oil

Mixer

Aqueous gelatin solution (40–60°C)

Aqueous gum arabic solution (40–60°C)

Oil-in-water emulsion

Adjust pH (e.g.,4.0–4.6)

Cool (to gel coacervate)

Mixer

Crosslink

Harvest microcapsules

Water (40–60°C)

Figure 7.1. Flow diagram of gelatin gum arabic (GGA) complex coacervation encapsulation procedure (from Green and Schleicher, 1957, with permission).

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Chapter 7

formed by the complex coacervation of gelatin are typically chemically cross-linked with glutaraldehyde (glut) before they are isolated. Today, complex coacervation encapsulation protocols still follow the basic Green and Schleicher (1957) procedure shown in Figure 7.1. Specific concentrations and types of the polymers involved may vary, but the three-step protocol of emulsion formation, coacervate formation, and coacervate gelation is still used. Numerous variations of this process have appeared since 1957, because many polyanions other than GA have been shown to interact with gelatin to produce complex coacervates suitable for microcapsule formation. This has led to the development of a broad family of complex coacervation encapsulation procedures. Specific coacervation procedures acceptable for the formation of flavor-loaded microcapsules are those in which gelatin interacts with food-grade polyanions such as GA, sodium alginate, carrageenan, pectin, CMC, gellan, and sodium polyphosphate. Combinations of these polyanions can also be used. Significantly, the data in Table 7.1 show that properties of the coacervate phase formed in each protocol differs in some manner. Even if the difference is small, considerable time may be required to experimentally define conditions required for suitable capsule formation. Table 7.3 is a list of a number of complex coacervation encapsulation protocols reported by various workers in journals or patents. It is not an exhaustive list, but the references cited provide information about a number of gelatin-based complex coacervation systems that are candidates for flavor oil encapsulation. All the protocols are based on materials that the author regards as suitable for encapsulating food flavors. It is interesting that no two protocols disclosed in Table 7.3 are similar. They all have an emulsification, coacervation, and cooling step, but the conditions under which these are carried out are not standardized; that is, a standard protocol is not followed. Some workers use Type A gelatin, while others use Type B. Gelatin bloom strength varies. Reported coacervation pH values fall between 3.0 and 5.5. Some workers adjust pH with acetic acid, while others use HCl. Gelatin involved carries a positive charge in the 3.0–5.5 pH range and serves as the polycation in all but one of the complex coacervation encapsulation systems cited in Table 7.3. The sole case where this may not be the case is the coacervation of Type B gelatin with chitosan at pH 5.25–5.5 (Remunan-Lopez and Bodmeier, 1996). If this system is a complex

Table 7.3.

Complex coacervation encapsulation protocols based on food-grade shell materials

Gelatin

Polyanion

Coacervation (pH)

References

Type B, 225 bloom Type B, 225 bloom Type A Type A, 300 bloom Type A, 275 bloom Type B, 175 and 225 bloom Type A, 175 bloom Type A Type A, 275 bloom Fish gelatin Type A

CMC Acacia Acacia CMC Pectin NF Chitosan glutamate

3.0–4.0 (0.1 M HCl) 3.9 (1 M HAc) 4.2 (glacial, acetic acid) 4.4 (10% HAc) 3.2–4.6 (0.5 M HCl) 5.25–5.50 (0.5 M HCl)

Gellan Sodium alginate Sodium pyrophosphate CMC/gum arabic Gum arabic

3.5–5.50 (0.5 M HCl) 3.5–4.5 (0.5 N HCl) 4.5 (10% acetic acid) NA 3.9–4.7 (10% acetic acid)

Koh and Tucker (1988a, b) Jegat and Taverdet (2000) Mayya et al. (2003) Kim et al. (2001) McMullen et al. (1984) Remunan-Lopez and Bodmeier (1996) Chilvers and Morris (1995) Joseph and Venkataran (1995) Yan (2005) Soper (1997) Saeki and Hosoi (1984)



159

coacervation system, the gelatin must act as the polyanion, while chitosan is the polycation. At pH 5.25–5.5, such protocols should be limited to Type B gelatins. The pI of Type A gelatin is typically 8–9, so its complex coacervation with chitosan should be limited to pH values above this. Several of the studies referenced in Table 7.3 explore how various parameters affect microcapsule formation by complex coacervation. For example, Jegat and Taverdet (2000) found that the relationship of stirring rate and size of capsules produced by gelatin-GA coacervation agrees well with predictions of the inertial breakup theory. Mayya et al. (2003) reported that addition of low concentrations of sodium dodecyl sulfate (SDS) to the aqueous phase during emulsification promotes GGA coacervate capsule shell formation on dispersed paraffin oil droplets. The SDS concentration used was well below its CMC. These workers suggest that SDS causes deposition of a two-layer shell. Duquemin and Nixon (1985) examined the effect of SDS and cetrimide on complex coacervate formation and encapsulation by complex coacervation. Three SDS concentrations were used: 0.07, 0.2, and 0.35 w/v%. The 0.07 w/v% SDS solution was below the CMC of SDS. Although the weight of coacervate obtained at pH 4.35 and 40°C decreased linearly with increasing SDS concentration, 0.07 w/v% SDS caused very little reduction. Significantly, Duquemin and Nixon (1986) reported that 0.07 w/v% SDS caused a major reduction in the amount of core material (phenobarbitone) encapsulated. The author has historically avoided the addition of surfactants to a complex coacervation system. I am concerned that surfactants will have a negative effect on capsule quality. In my experience, nonionic surfactants have consistently had a negative effect on capsule quality; this is consistent with the observations of Luzzu and Gerraughty (1964). Nevertheless, the positive results with an anionic surfactant reported by Mayya et al. (2003) coupled with the positive result with a cationic surfactant (cetrimide) reported by Duquemin and Nixon (1985) indicate that further studies of how ionically charged surfactants affect complex capsule formation are warranted. Although it is not complex coacervation, the report by Vinietsky and Magdassi (1997) that soybean oil droplets are encapsulated by an SDS–Type A Gelatin complex is interesting. Encapsulation occurred at pH 4 and an SDS concentration of 1.5–2.0 mM. This SDS concentration range is below the CMC of SDS. The gelatin concentration after SDS addition was 0.3 mM. Yan (2005) claims the formation of a microcapsule structure in which an agglomeration of primary microcapsules is encapsulated by an outer shell. Each individual primary microcapsule in the agglomeration is claimed to have a primary shell and this agglomeration is encapsulated by an outer shell. Yan (2005) described the formation of this capsule structure by a GP complex coacervation procedure in which the aqueous phase contained 0.5% sodium ascorbate. The first step is to prepare an 8.33 w/w% gelatin and 0.5% sodium ascorbate solution in water at 50°C. A fish oil concentrate is emulsified in this solution under high shear. The resulting oil-in-water emulsion has oil droplets with an average size of 1 µm. After it is formed, the emulsion is diluted by addition of a 0.5% aqueous sodium ascorbate solution at 50°C. A 5% sodium polyphosphate plus 0.5% sodium ascorbate solution is then added. After the pH is adjusted to 4.5, the system is cooled, thereby forming coacervates that coats the individual oil droplets, which creates primary microcapsules. The temperature at which this occurs and the rate of cooling to this temperature are not mentioned, but it is noted that the primary microcapsules begin to agglomerate as cooling is carried out to above the gel point of the coacervate. Upon further cooling of the system,

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Chapter 7

additional coacervate forms and coats the agglomerates of primary microcapsules, thereby creating an agglomerate of primary microcapsules with an outer shell and an average size of 50 µm. Once the system is cooled to 5°C, glut is added and allowed to react for 12 h with the suspended capsules in the system under continuous stirring for 12 h. The microcapsule suspension is subsequently washed with water and spray dried to give a free-flow powder. Two interesting complex coacervation encapsulation systems that contain an essentially nonionic polymer have been reported. Although such polymers are not believed to be directly involved in complex coacervate formation, they undoubtedly affect it in some manner. One system was reported by Jizomoto (1984). He reported that the addition of small amounts of a nonionic polymer like polyethylene oxide or poly (ethylene glycol) expanded the pH range over which a GGA complex formed. By using this approach, it was possible to prepare GGA capsules loaded with paraffin oil at pH 6.5. The pH range over which GGA coacervates were formed was 2–9. This type of system offers a possible method of encapsulating active agents sensitive to the acidic conditions characteristic of a typical GGA encapsulation system. The author views it as a process that combines complex coacervation with polymer–polymer incompatibility. The second procedure was reported by Xing et al. (1973). They prepared capsaicinloaded GGA microcapsules in the presence of low concentrations of hydroxylethyl cellulose (HEC), poly (vinyl alcohol) (PVA), and poly (vinyl pyrrolidone) (PVP). It was noted that the presence of HEC yielded GGA microcapsules with a better morphology and geometry than capsules prepared in the presence of PVA or PVP. These polymers were classified by the authors as surfactants, but it is possible that differences in their polymer–polymer incompatibility behavior could contribute to the observed results even at the low concentration used.

Cross-Linking of Gelatin-Based Coacervate Capsule Shells When initially formed, gelatin-based complex coacervate capsule shells are highly water swollen and melt if reheated. They also dissolve in warm aqueous media, thereby releasing their core. This latter property is highly desirable in many food applications, but it also poses problems because the isolation of discrete gelatin-based coacervate capsules that have not been cross-linked in some way is difficult. The shell of such capsules is highly water swollen and melts if subjected to relatively low levels of thermal energy. Extractive drying with a water-miscible solvent at low temperatures is one option, but extraction of core material by the extractive drying solvent must be minimized. In any case, drying capsules that have not been cross-linked in some manner is an issue. For this reason, it is common practice to treat gelatin coacervate shells in some way in order to stabilize them, so that they can be dried using conventional spray-drying techniques and fluidized bed units. Historically, this has been done by using aldehydes or tannins to crosslink gelatin-based capsule shells. Treatment with an aldehyde has been the most common approach taken. Formaldehyde and glut are two aldehydes cited in many publications. However, glut, a five-carbon-chain dialdehyde, is used by most commercial capsule producers. Glut effectively cross-links gelatin-based complex coacervates and insolubilizes them under conditions that rapidly and completely dissolve untreated capsules (1973). Glut uptake at 4°C by acid or alkaline precursor gelatin gels ranges from 0.9 to 1.4 mM/g gelatin. Initial solids content of these gels varied from 1.4 to 5.5 wt%, significantly lower than



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the 12–17 wt% initial solids content of the GGA gels treated with glut. GGA gels formed from both types of gelatins had a glut uptake of 0.54–0.65 mM/g gelatin when the reaction was carried out at 4°C. Glut uptake by GGA gels formed with acid precursor gelatin essentially doubled when the reaction temperature was increased to 28°C. This increase was attributed to temperature-dependent changes in the gel structure of the coacervate (1973). Since a 10 wt% GA solution did not react with a significant amount of glut, glut consumption by GGA coacervate gels is attributed to reaction with gelatin. The amount of glut reacting with the gelatin in a GGA gel at acid pH generally does not exceed the titratable amino content of the gelatin. Thus, glut produces a lightly cross-linked gel structure. Such cross-linked gels are largely insoluble in water, but retain an ability to swell in water. They are also able to absorb moisture at a relative humidity (RH) above 70%. Thus, the shell of glut-treated GGA and other complex coacervate capsules remains sensitive to moisture. At high RH, the amount of moisture absorbed by such shells is sufficient to plasticize them and thereby reduce their barrier properties significantly. For this reason, glut-treated complex coacervate microcapsules loaded with volatile flavors are typically unstable at high RH. This should also be true for such capsules loaded with oxygensensitive flavors stored in air at high RH. Although glut-treated complex coacervate capsules have been approved for specific flavor uses, the safety of capsules cross-linked with aldehydes such as glut has always been open to question. For this reason, interest in an alternate ways to stabilize complex coacervate capsule shells has existed for some time. The goal is to produce stabilized capsules that are broadly accepted as food grade. One of the first alternate approaches involved posttreating complex coacervate capsules with aqueous tannic acid solutions. Tannic acid rapidly and dramatically shrinks coacervate capsule shells, thereby reducing the water content of the capsule shells and greatly increasing their ease of capsule isolation and drying. However, the interaction of tannic acid with gelatin is intense and rapid. This makes it difficult to achieve precise control of the treatment process required in order to obtain reproducible results. When capsules with a continuous core/shell structure and high oil loading are treated, the effective degree of cross-linking achieved can be so intense that the capsules crack and break open upon drying. Lot-to-lot variations in tannic acid properties are another issue. Nevertheless, various workers continue to explore the use of tannins and natural phenolic compounds as cross-linking agents for coacervate gels. Xing et al. (2004) reported that they successfully treated GGA capsules with tannins. The GGA capsules were prepared in the presence of HEC, PVA, or PVP and subsequently immersed for 10 h in pH 8–9 aqueous media that contained 2.4 w/v% tannins. The capsules so treated contained upon drying 19% core material, much lower than the core content of continuous core/shell capsules typically produced by complex coacervation. Further, the core material was sonicated in a GA/HEC solution for 30 min. before gelatin was added to the system and coacervation induced. This suggests that the capsules isolated had a multicore structure and not a continuous shell/core structure. Stresses that tannins induce when they rapidly shrink a water-swollen capsule shell may have less effect on capsule stability when the core material is distributed in small droplet form throughout the final dry particle. Strauss and Gibson (2004) reported that treating gelatin and pectin-gelatin coacervate gels with plant phenolics increased their mechanical strength and thermal stability as well as reduced swelling. They interpreted their results as being consistent with a picture of polyphenols reacting under oxidizing conditions with gelatin side chains to form covalent cross-links. It was noted that coffee, grape juice, and various other plant materials contain

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enough phenolics to be effective cross-linking materials, so that isolation of the active components was not necessary. The effect of plant phenolics on capsules with a gelatin-based coacervate shell was not reported. The effect of lot-to-lot variability of the natural product solutions on degree of effective cross-linking achieved was also not discussed. Another non-aldehyde route to chemical cross-linking gelatin-based complex coacervate capsule shells involves using transglutaminase (TG), an enzyme produced by microbial fermentation and sold in the United States by Ajinomoto Food Ingredients, Paramus, NJ. Dickenson reviewed the use of covalent cross-linking enzymes to introduce cross-links as a tool for controlling the rheology and stability of protein-based foods (Dickinson, 1997). He noted that in 1997 TG, an extracellular product, was the only commercially available cross-linking enzyme, although another enzyme, lysyl oxidase, should be of interest to food technologists. TG is commercially available, because it is readily isolated from the broth of fermented Streptoverticillium mobaraense. Ajinomoto literature stresses that its TG functions without calcium. This is important, because many common food proteins such as casein tend to precipitate at relatively low calcium ion concentrations (Dickinson, 1997). TG introduces cross-links between protein molecules, because it catalyzes the acyl transfer reaction between the γ-carboxyamide group of a glutamine residue of a protein and the ε-amino group of a lysine residue of a protein (Folk and Finlayson, 1977). The two protein molecules may be different. Various Ajinomoto data sheets specify the range of pH and temperature conditions under which Activa®, the trademarked name for Ajinomoto’s commercial TG, will function. The optimal temperature range is 50–55°C, while the optimal pH range is 6–7. The enzyme functions outside these ranges, although at a reduced activity level. Since uncross-linked gelatin-based coacervate gels typically melt above 35–40°C and swell significantly at neutral pH values, TG –induced cross-linking of such gels will not be carried out under optimal conditions. Cho et al. (2003) used TG to crosslink capsules loaded with fish oil that were formed by a double emulsion process. The capsule shell was isolated soy protein (ISP). The fish oil was first emulsified in a 10% ISP aqueous solution that contained 0.025% TG. This emulsion was then dispersed in corn oil that contained 3% Span 80. The resulting double emulsion was warmed to 37°C and held at this temperature for 4 h. During this time, the protein solution was converted to a gel. Soper and Thomas (2000, 2001) disclosed a process in which TG was used to cross-link the shell of capsules formed by complex coacervation. The aqueous capsule system described as the example in their patents was formed by complex coacervation of gelatin by a CMC–GA mixture. The aqueous capsule system produced was cooled to 5–10°C at which temperature its pH was adjusted to 7.0. TG was slowly added to the system and allowed to react with the capsules for 16 h at 10°C. The TG was then inactivated by lowering the system’s pH to 2.75 with concentrated citric acid. No specific properties of the capsules cross-linked by TG were presented.

Complex Coacervation Encapsulation Technology Issues Complex coacervation encapsulation procedures have existed for 50 years and continue to be used to produce large amounts of microcapsules for various commercial applications. Nevertheless, such procedures have a number of issues. Consistent quality control of complex coacervation encapsulation processes can be a challenging task, because final capsule



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properties are very sensitive to small changes in the many variables associated with complex coacervation. Since complex coacervation is a polymer phase-separation process, reproducibility is very dependent on solution properties of the polymers involved. Lot-to-lot variations in properties of the polymers used will impact process control. The degree of phase separation that occurs in a specific complex coacervate encapsulation system is influenced by the polymers involved, their MW, ionic charge density, and concentration. Variations in these properties affect polymer phase-separation behavior. The source, type of gelatin used, acid or alkaline precursor, and bloom strength are variables that must be controlled. Since gelatin is hydrolytically unstable, thermal conditions throughout the encapsulation protocol must be controlled. The ratio of polymers present in the complex coacervate system is another factor. System pH, temperature, and salt ion content also influence the phenomenon and must be controlled. Other factors that may affect coacervation include the type of acid used to adjust system pH as well as the presence of surfactants in the system. Soper et al. (2000) also describe a number of factors that affect flavor encapsulation by complex coacervation. The core material being encapsulated is another process variable. This is particularly true when the core material is a complex mixture of many components of differing polarity. Flavors are a specific example of such types of core materials. In order to illustrate this point, Table 7.4 lists experimentally determined compositions of a sample of orange, lemon, and mint oils (Arneodo et al., 1988/1989). Although these flavor oils are composed of a mixture of hydrocarbons, ketones, aldehydes, alcohols, esters, and other unidentified components, the dominant component is limonene. The data in Table 7.5 (Arneodo et al., 1988/1989) establish that some of the minor components present in orange and lemon oil partition into the aqueous phase. Limonene glycol, a limonene-degradation product that impacts citrus oil quality, was present in the aqueous phase equilibrated with both oils. Table 7.4.

Composition of orange oil, lemon oil, and mint oil flavors

Component

Orange oil

Lemon oil

Mint oil

96 0.7 2 0.47 0.05

73 21.8 1.8 1.2 0.9

0.9 33.5 60.4 60.4 2.9

Hydrocarbons (limonene, others) Ketones Aldehydes Alcohols Esters

Table 7.5. Composition of orange oil, lemon oil, and mint oil that partition at 30°C and 50°C (component concentration in aqueous phase, ppm)

Component Hydrocarbons (limonene, others) Ketones Aldehydes Alcohols Esters Limonene glycol

30°C

Orange oil 50°C

Lemon oil 30°C 50°C

30°C

Mint oil 50°C

2

6

8

36

12 31

10

12

8

5

185 9 212 8

185 245 7

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Even though limonene is the major component of orange and lemon oils, the interfacial behavior of both oils is dominated by polar components present in small amounts. The interfacial tension of D-limonene against water at 50°C declines from 35 to 23 mJ/m2 over 5 h (Arneodo et al., 1988). These interfacial tension values are much greater than those obtained with orange and lemon oils against water at 50°C (46). In contrast, the initial interfacial tension value of 1-octanol against water at 50°C is 8 mJ/m2 and it declines to 2 mJ/m2 after 5 h. The interfacial tension of decanal against water at 50°C declines over 5 h from an initial value of 10–6 mJ/m2. Although both of these compounds are present in orange and lemon oils in small amounts, they have an affinity for the oil–water interface and undoubtedly impact the interfacial activity of both oils. Interfacial tension values of GA coacervate and supernatant phases measured at 50°C against D-limonene decay from an initial value of 14–10 mJ/m2 after 5 h (Arneodo et al., 1988). Since the coacervate phase is a much more concentrated polymer solution, it is surprising that the two interfacial tension decay curves overlap as well as they do. The slope of the interfacial tension decay curve decreases significantly at an interface age of 1 h after which linear slow decay continues up to at least 5 h. Interfacial tension values of orange and lemon oils measured against water at 25°C, 30°C, or 50°C decline significantly as the interface ages over a 5–10 h period (Arneodo et al., 1988). Initial interfacial tension values are 4–8 mJ/m2. Values after interfacial aging range from 6 mJ/m2 to a value too low to be measured by the Wilhelmy plate method. The rate of interfacial tension decline is reduced but not eliminated when the system temperature was lowered to 1.2°C. The interfacial tension behavior of both oils against the supernatant phases isolated from GGA, GP, and GAlg coacervate systems was similar to that observed with water. This was not surprising, because the supernatant phases are dilute polymer solutions. However, it is interesting that the interfacial tension of GGA, GP, and GAlg coacervate phases against orange and lemon oils is similar to that observed with water. The primary difference with the coacervate phases is that the rate of interfacial tension decline was generally faster at the same temperature than that observed with water and an interfacial tension too low to measure by the Wilhelmy plate method was observed more often. Interfacial tension aging at an oil/aqueous phase interface is an indication of interface instability. The precise cause of this instability is difficult to define because it can be caused by many factors. Furthermore, a very small amount of interfacially active material can have a major effect on interfacial tension. For flavor encapsulation procedures, the possibility that interfacial aging is due to one or more chemical reaction(s) at the flavor oil/water interface is a concern. Candidate reactions in a gelatin-based complex coacervation encapsulation system include oxidation, hydrolysis, and aldehyde condensation with any free primary amino groups in the coacervate. However, interfacial aging could also be caused by slow physical adsorption of interfacial active agents at the interface and slow rearrangements of the molecules in the adsorbed layer. Although polymer solutions frequently show this type of behavior, the author favors interfacial chemical reactions as the primary cause of interfacial aging. This point of view is based on several experimental observations. First, dispersed precipitate particles or a continuous intact film often formed at citrus oil/water interfaces aged in several hours. When such systems were agitated, the aqueous phase became cloudy. A second observation is the significant interfacial tension aging that both oils experience against highly purified water. Gelatin and other polymers that could contribute to prolonged interfacial aging and interfacial film formation are not initially present



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in such systems. Finally, interfacial aging can be markedly reduced by reducing the temperature of the system to 2°C. Gelatin has been the dominant polycation in complex coacervation encapsulation protocols since 1957, because it is readily available at reasonable cost and forms a gel structure upon cooling, thereby setting an embryonic capsule shell. Nevertheless, the use of gelatin creates a number of issues. For example, the appearance of mad cow disease raised serious concerns about the safety of bovine gelatin for human consumption. This issue prompted global gelatin manufacturers to support extensive studies of the possible transmission of prions via gelatin consumption. These studies have concluded that commercially available food grades of gelatin are not a potential source of mad cow disease transmission. Nevertheless, residual concern about its safety remains; if not for mad cow disease, other diseases may appear in the future. Web sites posted by the Gelatin Manufacturers of Europe (GME) or Gelatin Manufacturers of Asia Pacific (GMAP) provide a means of monitoring the regulatory status of various types of gelatin. Another gelatin issue is the reality that food products must increasingly meet global dietary requirements. This has promoted a search for materials that can replace beef and pork gelatins. Fish skin gelatin is one candidate. Soper (2001) disclosed the formation of capsules by coacervation of warm water fish gelatin with a CMC/GA mixture. Fish skin gelatin is currently much more expensive than beef or pork gelatin but can be used. Residual concern about the safety of gelatin has sparked interest in producing microcapsules by complex coacervation of other proteins. Weinbreck et al. (2003) disclose an encapsulation procedure that is based on the complex coacervation of whey protein. Although a range of polyelectrolytes is claimed to be suitable for the coacervation process, GA is cited as the preferred one. The preferred coacervation pH range is 2.5–4.5. The capsules produced can be hardened by treatment with an aldehyde or enzyme. A claimed feature of their process is that it can be carried out at or below room temperatures.

Solvent Exchange: A Unique Property of Complex Coacervate Microcapsules An interesting feature of gelatin-based complex coacervate microcapsules is their ability to undergo solvent exchange; that is, a water-immiscible liquid originally encapsulated within a complex coacervate shell can be exchanged with a second, chemically different liquid that has finite water miscibility. The exchange process occurs by diffusion through intact capsule shells and broadens the range of core materials that can be incorporated in a complex coacervate capsule. Because of solvent exchange, capsules formed by complex coacervation can be loaded with liquids and flavors that cannot be encapsulated at the time of capsule formation. Figure 7.2 is a simplified flow diagram of the Brynko and Olderman solvent exchange procedure (Brynko and Olderman, 1970). The first step is to prepare complex coacervate microcapsules loaded with an oil that is water immiscible. For food applications, the oil will be edible. Capsules to be subjected to solvent exchange must have a water-swollen shell. It may be chemically cross-linked or uncross-linked. Once such capsules are available, they are subjected to the solvent exchange treatment. In one case, Brynko and Olderman (1970) dispersed a water-wet filter cake of oil-loaded capsules in a concentrated (80 w/w%) aqueous sorbitol solution for a defined time (e.g., 30 min). The purpose of this treatment was to introduce into the capsule shell a finite amount of sorbitol, a compound

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Oil-loaded capsules Shell: Water-swollen Gelatin-based Solvent exchange liquid with finite H2O and core miscibility Agitation for several hours (exchange by diffusion) Anhydrous water-miscible solvent (e.g., ethanol) Brief agitation (extraction of water)

Isolation and drying

Dry capsules loaded with exchanged liquid

Figure 7.2. Simplified flow diagram of solvent exchange coacervation procedure (from Brynko and Olderman, 1970, with permission).

designed to plasticize the capsule shell. After excess sorbitol solution was removed from the capsule slurry, typically by filtration, a finite volume of ethanol was added to the system. Food-flavoring agents may be dissolved in the ethanol. After a finite diffusion or solvent exchange time (e.g., 30 min), excess ethanol solution may be removed from the system by decantation or filtration and replaced with a fresh ethanol solution. This cycle is repeated until the desired extent of solvent exchange is achieved. Brynko and Olderman (1970) completed their solvent exchange process by immersing the capsules in excess anhydrous ethanol free of solute. The objective is to remove the last remaining traces of water from the capsule shell, thereby sealing them. After the capsules are dried, they form a free-flow powder. Brynko and Olderman (1970) teach that the shell of a complex coacervate capsule must be water-swollen in order to successfully undergo solvent exchange. The water may be present either because the capsule was never dried after formation or because water was added after the capsule had been dried. Water is essential. It causes complex coacervate shells to swell and become porous to liquids that have finite water miscibility. This enables the diffusion of such liquids into the interior of capsules. Since solvent exchange is a diffusion process, a finite time is required. Solvent exchange is a diffusion-controlled equilibration or partitioning process, so complete removal of the oil originally carried by a capsule is difficult to achieve. A small but finite amount of oil is typically left in a capsule after solvent exchange is deemed complete. In some cases, a water-swollen coacervate capsule shell acts as a semi-permeable membrane that allows diffusion of the solvent exchange liquid into the capsule, but not diffusion of the oil out. The resulting increase in liquid content of the capsule may be so significant that the capsules visibly increase in diameter. Although water must be present in the shell of a complex coacervate when solvent exchange is carried out, its presence in the capsule shell after completion of the solvent exchange process is detrimental to prolonged storage stability. Brynko and Olderman (1970) correlated retention of a solvent exchange with its dielectric constant. They report



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that single liquids with finite water miscibility and a dielectric constant below 20 yield stable capsule powders, whereas liquids with a dielectric constant above 20 do not. Since the dielectric constant of ethanol, a desirable exchange solvent, is 24.3, ethanol-loaded capsules prepared by solvent exchange are unstable. The lower the dielectric constant of the exchange liquid, the more stable the capsules. Mixtures of dielectric solvent liquids with low dielectric constants can be used as long as the dielectric constant of the mixture is <20. Thus, stable capsules that contain a finite concentration of ethanol can be prepared as long as the other solvents present in the capsule have a low dielectric constant and the solvent mixture has a dielectric constant below 20, preferably below 14. The instability of capsules loaded with a high dielectric constant solvent is attributed to their ability to readily absorb water from the atmosphere in which the capsules are stored. The absorbed water plasticizes the capsule shell, thereby facilitating rapid solvent release. Brynko and Olderman (1970) note that capsules isolated after solvent exchange with butyl acetate contain 0.01% water. These have excellent storage stability, because the dielectric constant of butyl acetate is 5 and butyl acetate does not promote water absorption from the atmosphere under typical conditions (e.g., RH <70%). Although Soper et al. (2000a, b) also disclose a solvent exchange procedure for preformed capsules. In one example, capsules loaded with purified vegetable oil were formed by the complex coacervation of gelatin with a mixture of GA and sodium CMC. Both chemically cross-linked and uncross-linked capsules were used. As noted by Brynko and Olderman (1970), Soper et al. (2000a, b) require the shell of capsules that are candidates for solvent exchange to be water swollen. Thus, capsules that were dried after formation were placed for 5 min in a flavor-water mixture. They were subsequently transferred to a closed plastic container and incubated for 24 h before use. The inventors note that the shell of capsules subjected to their solvent exchange procedure can be treated in order to prevent removal of flavor from microcapsules and water removal from the shells was specifically cited. The importance of residual water to dry capsule stability was not referenced, but it is reasonable to suggest that high humidity will affect storage stability of capsules subjected to solvent exchange, as disclosed by Soper et al. (2000) process. Soper et al. (2000, 2001) do not discuss the need for the solvent exchange system to remain in one phase throughout the solvent exchange process nor the effect of the exchange solvent’s dielectric constant on solvent exchange. Soper et al. (2000) report that capsules with water-swollen shells can absorb flavors from the gas phase. They placed oil-loaded capsules having a water-swollen shell in a container and purged them with a loaded gaseous phase that contained an aroma. After a finite purging time, 0.5–5 h depending on the aroma, the aroma absorbed by the capsules could be detected. A variety of applications were cited, including the separation and concentration of volatile hydrophilic aroma components from hydrophobic components.

Summary Complex coacervation encapsulation technology is versatile and adaptable. Capsules produced by this technology have many interesting features, which continue to attract interest in them. Soper (1995) discusses applications of flavors encapsulated by complex coacervation. Such capsules are prime candidates for flavor oil encapsulation. They offer food technologists a high degree of versatility and flexibility. Microcapsules with sizes ranging from a few microns to over a millimeter in diameter can be produced. Such capsules typically carry a flavor payload of 60–90 wt%, although lower and higher payloads can be produced.

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The capsules can be supplied as an aqueous slurry or dry powder. Drying is typically done in a fluidized bed or spray drier. Capsules supplied as aqueous slurries are able to withstand finite handling or processing stresses, because water-swollen complex coacervate shells are rubbery and resist failure. Such encapsulation protocols are not free of limitations or issues including: component partitioning during capsule manufacture, moisture sensitivity during storage, and reaction of aldehyde components of flavors with gelatin-containing shells on storage. Nevertheless, the technology continues to diversify and expand. Because many of its characteristic properties remain uncharacterized and unexploited, it is a fruitful area for further study.

References Arneodo, C., Baszkin, A., Benoit, J.-P. and Thies, C. 1988/1989. Interfacial studies of essential oil-water systems. Colloids and Surfaces 34: 159–169. Arneodo, C., Baszkin, A., Benoit, J.-P. and Thies, C. 1988a. Interfacial tension behavior of citrus oil components, Absts. 6th International Conference on Surface and Colloid Science, Hakone, Japan, p. 106. Arneodo, C., Baszkin, A., Benoit, J.-P. and Thies, C. 1988b. Interfacial tension behavior of citrus oils against phases formed by complex coacervation of gelatin, In Flavor Encapsulation, S.J. Risch and G.A. Reineccius, eds., American Chemical Society, Washington, DC, Chapter 15. Brenner, J. 1983. The essence of spray dried flavors: the state of the art. Perfumer and Flavorist 8: 40–44. Brynko, C. and Olderman, G.M. 1970. Replacement of capsule contents by diffusion, US Patent 3,516,943 (June 23, 1970). Bungenberg de Jong, H.G. 1949. Complex colloidal systems, In Colloid Science, Vol. II, H.R. Kruyt, ed., Elsevier, Chapter 10. Burgess, D.J. 1990. Practical analysis of complex coacervate systems. J. Colloid and Interface Sci. 140: 227–238. Chilvers, G.R. and Morris, V.J. 1987. Coacervation of gelatin-gellan gum mixtures and their use of microencapsulation. Carbohydrate Polymers 7: 111–120. Cho, Y.-H., Shim, H.K. and Park, J. 2003. Encapsulation of fish oil by an enzymatic gelation process using transglutaminase cross-linked proteins. J. Food Sci. 68: 2717–2723. Commandur, B., Arneodo, C., Benoit, J.-P. and Thies, C. 1989. A viscosity study of gelatin-based complex coacervates. Proceed. Intern. Symp. Control. Rel. Bioact. Mater. 16: 279–280. Duquemin, S.-J. and Nixon, J.R. 1985. The effect of sodium lauryl sulphate, cetrimide and polysorbate 20 surfactants on complex coacervate volume and droplet size. J. Pharm. Pharmacol. 37: 698–702. Duquemin, S.-J. and Nixon, J.R. 1986. The effect of surfactants on the microencapsulation and release of phenobarbitone from gelatin-acacia complex coacervate microcapsules. J. Microencapsulation 3: 89–93. Dickinson, E. 1997. Enzymic cross-linking as a tool for food colloid rheology control and interfacial stabilization. Trends in Food Science and Technology 8: 34–339. Folk, J.E. and Finlayson, J.S. 1977. The ε-(γ-glutamyl)lysine crosslink and the catalytic role of transglutaminase. Adv. Protein. Chem. 31: 1–133. Goubet, I., Le Quere, J.L. and Voilley, A.J. 1998. Retention of aroma compounds by carbohydrates: influence of their physicochemical characteristics and their physical state. A review. J. Agric. Food Chem. 46: 1981–1990. Green, B.K. and Schleicher, L. 1957. Oil-containing microscopic capsules and method for making them, US Patent 2,800,457, July 23. Jegat, C., Taverdet, J.L. 2000. Stirring speed influence study on the microencapsulation process and on the drug release from microcapsules. Polymer Bulletin 44, 345–351. Jizomoto, H. 1984. Phase separation induced in gelatin-base coacervation systems by addition of water-soluble nonionic polymers I: Microencapsulation. J. Pharm Sci. 73: 879–882. Kerkof, P.J. and Thijssen, H.A. 1974. Retention of aroma components in extractive drying of aqueous carbohydrate solutions. J. Food Technol. 9: 415–423. Kim, J.-C., Song, M.-E., Lee, E.-J., Park, S.-K., Rang, M.-J. and Ahn, H.-J. 2001. Preparation and characterization of triclosan-containing microcapsules by complex coacervation. J. Dispersion Science and Technology 22: 591–596.



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Koh, G.-L. and Tucker, I.G. 1988a. Characterization of sodium carboxymethylcellulose-gelatin complex coacervation by viscosity, turbidity and coacervate wet weight and volume measurements. J. Pharm. Pharmacol. 40: 233–236. Koh, G.-L. and Tucker, I.G. 1988b. Characterization of sodium carboxymethylcellulose-gelatin complex coacervation by chemical analysis of the coacervate and equilibrium fluid phases. J. Pharm. Pharmacol. 40: 309–312. Leuenberger, B.H. 1991. Investigation of viscosity and gelatin properties of different mammalian and fish gelatins. Food Hydrocolloids 5: 353–361. Liu, X.-D., Atarashi, T., Furuta, T., Yoshii, H., Aishima, S., Ohkawara, M. and Linko, P. 2001. Microencapsulation of emulsified hydrophobic flavors by spray drying. Drying Technology 19: 1361–1374. Luzzu, L.A. and Gerraughty, R.J. 1964. Effect of selected variables on the extractability of oils from coacervate capsules. J. Pharm Sci. 53: 429–431. Mayya, K.S., Bhattacharyya, A. and Argillier, J.-F. 2003. Micro-encapsulation by complex coacervation: influence of surfactant. Polym. Int. 52: 644–647. McMullen, J.N., Newton, D.W. and Becker, C.H. 1984. Pectin-gelatin complex coacervates II: effect of microencapsulated sulfamerazine on size, morphology, recovery, and extraction of water-dispersible microglobules. J. Pharm. Sci. 73: 1799–1803. Menting, L.C. and Hoogstad, B. 1967. Volatiles retention during the drying of aqueous carbohydrate solution. J. Food Sci. 32: 87–90. Re, M.I. 1998. Microencapsulation by spray drying. Drying Technology 16: 1195–1236. Reineccius, G. 2004. The spray drying of food flavors. Drying Technology 22: 1289–1324. Remunan-Lopez, C. and Bodmeier, R. 1996. Effect of formulation and process variables on the formation of chitosan-gelatin coacervates. International Journal of Pharmaceutics 135: 63–72. Rulkans, W.H. and Thijssen, H.A. 1978. Retention of organic volatiles in spray-drying aqueous carbohydrate solution. J. Food Technol. 7: 95. Saeki, K. and Hosoi, N. 1984. Microencapsulation by a complex coacervation process using acid-precursor gelatin. Appl. Biochem. Biotechnol. 10: 251–254. Schmitt, C., Sanchez, C., Desobry-Banon, S. and Hardy, J. 1998. Structure and technofunctional properties of protein-polysaccharide complexes: a review. Critical Rev. Food Sci. and Technol. 38: 689–753. Soper, J.C. 1995. Utilization of coacervated flavors, In Encapsulation and Controlled Release of Food Ingredients, S.J. Risch and G.A. Reineccius, eds., American Chemical Society, Washington, DC. Soper, J.C. 1997. Method of encapsulating food or flavor particles using warm water fish gelatin and capsules produced therefrom. US Patent 5,603,952 (February 18, 1997). Soper, J.C. and Thomas, M.T. 2000. Enzymatically protein-encapsulating oil particles by complex coacervation. US Patent 6,039,901 (March 21, 2000). Soper, J.C. and Thomas, M.T. 2001. Enzymatically protein-encapsulating oil particles by complex coacervation. US Patent 6,325,951 (December 4, 2001). Soper, J.C., Kim, Y.D. and Thomas, M.T. 2000a. Method of encapsulating flavors and fragrances by controlled water transport into microcapsules. US Patent 6045835 (April 4, 2000). Soper, J.C., Yang, X. and Thomas, M.T. 2000b. Method of encapsulating flavors and fragrances by controlled water transport into microcapsules. US Patent 6106875 (August 22, 2000). Strauss, G. and Gibson, S.M. 2004. Plant phenolics as cross-linkers of gelatin gels and gelatin-based coacervates for use as food ingredients. Food Hydrocolloids 18: 81–89. Thies, C. 1973. The reaction of gelatin-gum Arabic coacervate gels with glutaraldehyde. J. Colloid and Interface Sci. 44: 133–141. Thies, C. 1999. A Short History of Microencapsulation Technology, Microspheres, In Microcapsules & Liposomes, Vol. 1: Preparation & Chemical Applications, R. Arshady, ed., Citus Books, London, pp. 43–54. Thijssen, H.A.C. 1975. In Freeze Drying and Advanced Food Technology, S.A. Goldblith, L. Rey and W.W. Rothmayer, eds., Academic Press, London. Veis, A. 1970. Phase equilibria in systems of interacting polyelectrolytes, In Biological Polyelectrolytes, A. Veis, ed., Marcel Dekker, NY. Veis, A. and Aranyi, C. 1960. Phase separation in polyelectrolye systems. I. Complex coacervates of gelatin 64: 1203–1210. Venkataram, J.S. 1995. Indomethacon sustained release from alginate-gelatin or pectin-gelatin coacervates. Int. J. Pharm. 126: 161–168. Vinietsky, Y. and Magdassi, S. 1997. Microencapsulation by surfactant-gelatin insoluble complex: effect of pH and surfactant concentration. J. Colloid and Interface Sci. 189: 83–91.

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Weinbreck, F., De Kruif, C. and Schrooyen, P. 2003. Complex coacervates containing whey proteins. WO 03/106014 A1 (December 24, 2003). Xing, F., Cheng, G., Yang, B. and Ma, L. 2004. Microencapsulation of capsaicin by the complex coacervation of gelatin, acacia and tannins. J. Applied Poly. Sci. 91: 2669–2675. Yan, N. 2005. Encapsulated agglomeration of microcapsules and method for the preparation thereof. US Patent 6974592 (December 13, 2005).



8

Confectionery Products as Delivery Systems for Flavors, Health, and Oral-Care Actives Jamileh M. Lakkis

Introduction Despite consumers apprehension about sugar-based products, the confectionery market is currently experiencing record growth. Euromonitor International has estimated the global confectionery market at more than $142 billion in 2005. This surge is due to two main factors: first, the availability of sugar-free versions of traditional sugared products and second, the new trend in formulating confectionery products with functional actives that can deliver unique health benefits. The last two decades have witnessed an intense effort to shift the market positioning of confectionery products from just pleasantly tasting sweet snacks to a platform for delivering nutraceuticals, breath fresheners, nicotine, antimicrobial and dental health agents as well as drug actives. The latter category—including analgesics, insulin, antibiotics, and other pharmaceutical ingredients, although outside the scope of this book—will be referred to help explain the mechanisms of delivery and absorption. Functional confections are currently enjoying an unprecedented acceptability from consumers trying to increase their intake of functional and health-promoting ingredients such as vitamins, minerals, herbal extracts, etc. in a familiar food format, which does not signal illness and can be consumed discreetly. Successful examples of this category include Viactive® from McNeil, a calcium- and vitamin-containing chewy candy formulated for women, Orbit® chewing gum from Wrigley’s that claims teeth-cleaning benefits, mentholated lozenges such as Vicks® and Robitussin® that claim throat relief or nasal decongestion, Listerine Pocketpaks® from Pfizer, and Nicorette®, smoke-cessation chewing gum from GlaxoSmithkline. The first patent on functional confectionery products was granted to W.F. Semple in the nineteenth century for developing a dentifrice in the form of a chewing gum (Semple, 1869). However, the first commercial product claiming delivery of functional ingredients was a salicylic acid-containing chewing gum, Aspergum®, which was marketed in the United States in 1924 and is still available today. A breakthrough in utilizing chewing gums as delivery systems was documented in the clinical finding that smokers may be able to give up smoking by self-titrating the amount of nicotine they absorb (Fernö, 1973; Mulry, 1988; Silagy et al., 2002). This finding was the basis for the development and marketing of nicotine-containing chewing gums, where subjects can chew the gum to release and absorb the needed amounts of nicotine (Benowitz et al., 1987; Mulry, 1988). Despite these advances, the challenge for true commercial success of functional confections lies mainly in the inability of some formats to deliver therapeutic levels of health actives and the harsh conditions in the stomach that can sometimes degrade the active before it had the chance to reach its target site such as lower intestines or the blood stream. Unlike flavor delivery, where the only requirement is dissolution of the active from the dosage into

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the saliva and its extended release for a desired period of time, delivering therapeutic actives requires more elaborate capsule or delivery system design and an understanding of the physiology of absorption across membranes. Actives incorporated into a confectionery product must be transported from the dosage carrier to specialized tissues and epithelia and eventually to the target site in the blood stream or the cytoplasm of a particular cell group. Two types of oral delivery routes can be distinguished; these are local (target release site is the mouth or throat areas) and systemic (blood stream or specific organ or cell). In designing delivery systems, it is imperative to take into consideration not only the physiology and organizational structure of the oral cavity but also the physicochemical properties of the delivery system including dose concentration, format, residence time in the mouth, etc.

Physiology and Organization of the Oral Area Organs that constitute the oral area include the mouth, tongue, and esophagus (Figure 8.1). Within these organs, several regions can be differentiated that are critical for permeability and absorption (Squier et al., 1976). The mouth extends from the lips to the oropharynx at the rear; its temperature and humidity vary greatly during normal activities such as drinking and eating, thus impacting the active’s dissolution and its absorption. The oral cavity can be divided into two main regions (Figure 8.2), namely: 1. The oral cavity proper consisting of the tongue, hard and soft palates, and floor of the mouth. 2. The outer vestibule consisting of cheeks (buccal mucosa), maxillary (upper jaw), and mandibular (lower jaw) areas.

Figure 8.1.

Views of the oral cavity and pharynx.


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In humans, the tongue is essential for several processes including moving the food bolus around in the mouth, chewing, speech, sucking, and swallowing. The latter is achieved by virtue of the negative pressure created within the oral cavity. The tongue consists of a mass of interwoven, striated muscles interspersed with glands and fat and covered with mucus membrane tissues that are responsible for secreting small amounts of mucus. The tongue surface contains papillae, which are sensitive to food flavors along with several ridges that help grip the food article while the tongue agitates it during chewing. The tongue is a highly sensitive well-coordinated organ that occupies the middle of the mouth; therefore any device placed in the oral cavity should take this into consideration. The sublingual area moves extensively during eating, drinking, and speaking, thus impacting the residence time of food bolus or any delivery device placed in the oral cavity (Collins and Dawes, 1987). The inferior portion of the tongue (under surface leading from the tip of the tongue to the floor of the mouth) contains mucus membranes and is smooth and purple in color due to the many blood vessels present. The root contains bundles of nerves, arteries, and muscles that branch to the other regions. Nerves from the tongue receive chemical stimulation from food in solution which gives the sensation of taste. The esophagus is a muscular tube that connects the pharynx to the stomach. It is approximately 25-cm long and about 2-cm in diameter. Similar to the buccal area, the esophagus is lined with stratified squamous epithelium lining whereas the very remote portion (toward the stomach) is lined with columnar epithelia, which are highly specialized for absorption. The main role of the esophagus is to move ingested materials from the mouth area to the stomach and lower gastrointestinal tract (GIT). The esophageal epithelial area is non-keratinized and

Upper lip Underside of tongue Alveolar mucosa Hard palate Gingiva Soft palate Cheek

Floor of mouth

Tongue Lower lip

Masticatory mucosa Lining mucosa Specialized mucosa

Figure 8.2. Anatomical location and extent of masticatory, lining and specialized mucosa in the oral cavity (Squier and Kremer, 2001 with permission).

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is lined with mucus-secreting glands that help keep the esophagus moist and protect it from gastric acidity. Typical food transit time in the esophagus is very short (10–14 seconds). One peripheral system, the trigeminal nerve, is responsible for specialized sensations and constitutes an important part of the oral cavity. Its function resembles that of the spinal nerves, which are responsible for the sensation in the rest of the body. The trigeminal nerve is a cranial nerve comprised of three major branches: the ophthalmic nerve, the maxillary nerve, and the mandibular nerve. The sensory function of the trigeminal nerve is to provide conscious awareness of the face and mouth. The maxillary nerve carries sensory information mainly from the cheek, upper lip, upper teeth and gum, palate and roof of the pharynx. Mandibular nerve carries sensory information from the lower lip, lower teeth and gum, and floor of the mouth. The mandibular nerve carries touch/position and pain/temperature sensations from the mouth but not taste sensations. Unlike touch/position input that takes place immediately, pain/temperature sensation experiences a perceptible delay due to the unmyelinated slow-conducting nerve fibers. This type of sensation is mostly caused by a specific group of chemicals commonly referred to as “sensates” and which include substances that induce cooling, warming, tingle, and similar effects. Sensates have been used in confectionery formulations to provide perception of refreshment (cooling, tingle) or soothing (warming) and calming sensations.

Permeability and Barrier Functions of the Oral Cavity Permeability and barrier selectivity of the oral cavity are complex phenomena. A better appreciation for these functions can be gained by understanding the structure and critical functions of tissues, salivary glands and their secretions as well as their interactions (Rojanasakul et al., 1992). Table 8.1 shows variations in thickness of the oral mucosa in various regions of the human oral cavity. However, mucosal thickness does not explain variations in permeability in various regions of oral cavity.

Physiological and Structural Basis of Transport Routes (Plasma and Epithelial Membranes) Plasma Membranes Plasma membranes retain the contents of the cell and act as permeability barriers. They allow only certain substances to enter or leave the cell, though the rate of entry is strictly controlled. Hydrophobic materials enter the cells easily due to the presence of a lipoidal layer at the cell surface, commonly known as the bilayered lipid membrane, with bands Table 8.1. Thickness of various regions of the human oral cavity (Robinson, 2000 with permission) Region (microns)

Thickness

Skin Hard palate Attached gingival Buccal mucosa Floor of mouth

100 250 200 200–600 100–200



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approximately 3 nm in width and an overall thickness of between 8 and 12 nm (Curatolo, 1987). Plasma membranes are highly organized structures, where proteins in specific conformations act as structural elements, transport nutrients, and sample the cell environment. Lipid-soluble substances tend to diffuse along the plasma membranes of the cells while water can flow through transcellular routes by virtue of the small polar channels through these membranes.

Epithelial Membranes Most internal and external body surfaces are covered with epithelia, which contain a layer of basal lamina and structural collagen underlying layers of epithelial cells. There are several morphologically distinct epithelial types, namely, simple squamous (line blood vessels), simple columnar (line stomach and small intestines), and stratified squamous epithelium (line mouth and esophagus). The epithelium has a vertical dimension of 600 microns through the epithelial ridges and 250 microns through the areas overlying the connective tissue papillae. The buccal epithelium possesses some net charge, hence its permeability and selective ion transport. Assessing the role of epithelial layers can better be understood by differentiating between two criteria, namely permeability and permselectivity. The former refers to permeation magnitude (as quantified by electrical resistance), while the latter describes its qualitative ability to show preference for cations or anions or within a series of cations and anions (Fromter and Diamond, 1972; MacKnight and Leader, 1983). Epithelia of the epidermis, hard palate, and gingivae are keratinized and are known to be not very permeable to water. Earlier studies showed that these keratinized epithelia contain neutral lipids such as acylceramides and ceramides, which have been associated with a barrier function (Wertz and Downing, 1983). Epithelia of the soft palate, sublingual, and buccal area as well as those located in the floor of the mouth are nonkeratinized and have shown significant permeability to water presumably due to the absence of acylceramides (Squier and Hall, 1985).

Oral Mucosa The oral mucosa represents one type of epithelial membranes that secretes mucus (Figure 8.3). Similar to the skin and intestinal mucosa, oral mucosa mainly protects the oral cavity from harmful substances as well as facilitates absorption of chemical entities. The oral mucosa plays a protective role during mastication, which involves compression and shear forces. Areas such as the hard palate and attached gingivae have a textured surface to resist abrasion and are tightly bound to the underlying bone to resist shear forces. The cheek mucosa is elastic to allow for distension. Like the skin, the human oral mucosa consists of stratified squamous epithelia. However, unlike the skin, it is always maintained moist because of the presence of numerous salivary glands and does not show the presence of keratin. These dissimilarities make the oral mucosa more permeable than the skin (Chen and Squier, 1984; Gandhi and Robinson, 1988; Squier and Wertz, 1996). The mucosa of the human mouth is permeable to various vitamins such as thiamine, ascorbic acid and nicotinic acid. Several investigations have shown that the absorption characteristics of the oral mucosa were broadly similar to those of the small intestine of a rat (Evered and Mallett, 1983; Evered et al., 1980).

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Epithelium

Lamina

Submucosa

Figure 8.3.

Structure of the oral mucosa (Harris and Robinson, 1992 with permission).

Saliva Saliva is a mucus, viscous, colorless fluid that originates in the buccal and sublingual glands. It is a unique fluid that plays a significant role in controlling absorption and bioavailability of ingested actives both as an enhancer and as a barrier to permeability. Saliva forms a thin film (0.07–0.10 mm) of hypotonic nature (110–220 milliosmoles/lit) that lubricates and moistens the inside of the mouth. Saliva is believed to play a significant role in repairing injuries and tears in the oral area due to the abundance of hyaluronic acid molecules. pH of human saliva ranges from 7.4 to 6.2 depending on its flow rate (low to high flow rates). Certain foods such as carbohydrates, due to bacterial action, can reduce saliva pH to 3–4. Saliva is primarily composed of water, mucus, proteins, glycoproteins, mineral salts, and amylases. The composition of the saliva depends on the rate at which different cell types contribute to the final secretion: mucus secretion (due to the glycoprotein and mucin) and watery secretion (containing salivary amylase). The major ions are sodium, potassium, chloride, and bicarbonates (Weatherell et al., 1994). In the ducts of the salivary glands, sodium and chloride are reabsorbed but potassium and bicarbonates are secreted, thus, the electrolyte balance is altered depending on the rate of salivary flow. Other salivary enzymes include ptyalin, lingual amylases and so on (Chauncey et al., 1957; Lindqvist and Augustinsson, 1975; Tan, 1976). In order to be absorbed orally, the active must first dissolve in the saliva. Extremely hydrophobic materials do not dissolve well and are likely to be swallowed intact unless a specialized delivery system is used to present them to the mucosa. Saliva containing dissolved actives is constantly being swallowed, thus competing with buccal absorption.



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Keratinization Barrier function of the surface layers of the buccal epithelium depends on the intercellular lipid composition. Epithelia that contain polar lipids notably cholesterol sulfate and glucosyl ceramides are considerably more permeable to water than keratinized epithelia. Intracellular lamellae composed of chemically nonreactive lipids have been identified in the human buccal mucosa and may be relevant to drug permeability. There are intercellular barriers in the superficial layers of both keratinized and nonkeratinized oral epithelia that can limit the penetration of substances traversing the tissue by this route, especially polar molecules and electrolytes. Substances with a preferential solubility are more likely to pass along membranes and these may be limited by the formation of a keratin layer.

Membrane Coating Granules Membrane coating granules (MCGs) are spherical or oval organelles of about 100–300 nm in diameter found in many stratified epithelia and are believed to form major permeability barriers. MCGs appear to play a major filtration barrier role in the kidneys (Kanwar et al., 1980) by delaying or preventing the movement of large molecules such as proteins. They have also been found in both keratinized (gingivae) and nonkeratinized (buccal) epithelia (Hayward, 1979). These granules contain glycoproteins, formed by covalent linkage between glycosaminoglycans, mucopolysaccharide, and proteins. The glycosaminoglycans are highmolecular weight linear molecules with complex sequence. MCGs are also negatively charged molecules (abundant in sulfate and carboxyl groups). The glycosaminoglycan molecule occupies a much larger volume than other molecules with comparable size. These characteristics make the glycosaminoglycan molecule an effective diffusional barrier in particular against electrolytes and water in extracellular fluids.

Polarity Permeability routes across the oral mucosa can be classified into nonpolar and polar: (i) the non-polar route involves lipid elements of the mucosa, which partition the active into the lipid bilayer of the plasma membrane or into the lipid of the intercellular matrix; and (ii) the polar route involves passage of hydrophilic materials through aqueous pores in the plasma membranes of individual epithelial cells or ionic channels in the intercellular spaces of the epithelium. Whether a given nonelectrolyte will pass rapidly across the oral mucosa is determined by its partitioning between lipid and aqueous phases (Schanker, 1964). Substances with high lipid solubility will be transported across the lipidrich plasma membranes of the epithelial cells while water-soluble substances will pass through the intercellular spaces. An alternative classification involves passage through intercellular spaces between cells (i.e. the paracellular route) or transport into and across the cells (i.e. the transcellular route). The latter involves partitioning, cellular channel diffusion, and carrier-mediated transport (Blanchette et al., 2004). The paracellular route represents diffusive convective transport occurring through the intercellular space (Figure 8.4).

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Figure 8.4. The four mechanisms of transport across a cell monolayer (Blanchette et al., 2004 with permission).

pH The buccal epithelium has an isoelectric point (pH at which potential is zero) of 2.6. At neutral pH, the buccal epithelial membrane is negatively charged, relatively impermeable to anions and therefore functions as an ion-exchange surface for cations. At acidic pH values (i.e. below the isoelectric point), the membrane carries a net positive charge and becomes relatively impermeable to cations and functions as an anion exchanger. Although diffusion potential experiments have shown a higher relative permeability of potassium cation (K) over the chloride anion (Cl), information on the absolute permeabilities of these ions is lacking (Kaber, 1974; Lesch et al., 1989). As ionic strength increases, resistance decreases due to increased electrostatic shielding and therefore lower electrostatic potential barrier to permeation of ions and a reduction in membrane resistance.

Transport Mechanisms across Membranes Drugs and active components, except when given intravenously, must be transported across several biological barriers before reaching general circulation. Four transport mechanisms are known, namely: simple (passive) diffusion, facilitated diffusion, active transport, and pinocytosis. It is generally believed that most substances passing across the oral mucosa move by simple Fickian diffusion (Siegel et al., 1971). Only qualitative evidence of facilitated diffusion for small substances has been reported (Siegel, 1984). The oral mucosa employs an active uptake mechanism for a very few number of small molecules such as monosaccharides (Manning and Evered, 1976). In buccal epithelia, passive diffusion is, likely, the most frequent mechanism. 1. Passive diffusion is the transport across the cell membrane wherein the driving force for the movement is the concentration gradient of the solute. In orally administered actives, this absorption occurs in the small intestines. 2. Facilitated diffusion can best be described by the movement of molecules from a higher concentration to a lower one as a result of their random motion. Depending on the physical or chemical properties of the active, diffusion across biological membranes can take place through a lipid phase or along aqueous channels. In either situation, provided that



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an adequate concentration of the active is applied to one side of a membrane and there is sufficiently rapid removal of it from the other side, then a steady state is reached in which the rate of diffusion is directly proportional to the concentration of the active (this is known as Fick’s law). 3. Active transport involves the movement of molecules against a concentration gradient or of ions against an electrochemical gradient and requires the expenditure of metabolic energy. Some sugars and amino acids are transported across intestinal epithelia but are unlikely to take place across skin or oral mucosa (Kaaber, 1973). 4. Endocytosis is a process by which a large number of different cell types are capable of taking up solid particles (phagocytosis) or fluids (pinocytosis) from their external environment by engulfing the material in membranous vesicles. While cells of the oral epithelium are capable of taking up material by endocytosis, particularly in the basal and prickle layers, it does not seem a likely transport mechanism across an entire stratified epithelium (Berridge and Oschman, 1972).

Effect of Dosage Position in the Mouth Within the oral cavity, delivery of drugs can be classified into four categories: 1. Sublingual delivery, in which the dosage form is placed on the floor of the mouth under the tongue. 2. Buccal delivery, in which the formulation is positioned against the mucus membranes lining the cheeks. 3. Local oropharyngeal delivery, where the delivery vehicle is positioned to treat the mouth and throat. 4. Periodontal delivery to treat below the gum margin. It has been suggested that drug absorption through the sublingual mucosa is more effective than through the buccal mucosa, even though both these regions are nonkeratinized. The sublingual epithelium is, however, thinner and immersed in saliva, both of which aid absorption (Altman et al., 1960). When fluoride tablets were placed in the lower mandibular sulcus, fluoride concentrations were found to increase significantly in the region of the tablet, but there was no appreciable increase in salivary levels. In addition, relatively small amounts of fluoride had migrated to the opposite side of the mouth suggesting that the lower mandibular sulci are quite isolated from the remainder of the mouth. However, when the tablet was placed in the upper sulcus, the fluoride migrated some distance from the site of administration (Weatherell et al., 1984). Glucose was also found to behave in a similar fashion (Weatherell et al., 1989). It may be concluded that the site-specific differences are due to saliva movement and dilution of the test substance rather than the nature of the substance. Thickness of the salivary film will vary from place to place depending upon the proximity to the ducts of the major and minor salivary glands, separation of mucosal layers during speaking and mouth breathing. Weatherell et al. (1989) reported that glucose retention in the oral cavity was least under the tongue presumably due to (i) dilution and flushing by saliva, (ii) mechanical action of the tongue, and (iii) tendency for some glucose to disappear by absorption through the sublingual mucosa or in certain other areas by metabolism in the plaque. Despite the

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widespread use of the buccal absorption test, which expresses results as average “buccal permeability” through the whole oral mucosa, recent efforts have focused on differentiating permeability between structurally different regions of the oral mucosa (Beckett and Moffat, 1969; Tucker, 1988).

Advantages of the Oral Route for Drug Delivery Most research has focused on the absorption and bioavailability of actives in the GIT epithelial area of the stomach and lower intestines. Orally administered actives, however, and their subsequent transport across the oral cavity are less understood. Transport of actives across the oral route, nevertheless, has many advantages including: 1. Rapid action or onset of actives: The oral cavity is very rich in blood vessels (Table 8.2). Blood supply from the buccal mucosa, unlike the rest of the gastrointestinal tract, does not drain into the hepatic portal vein, since these peripheral areas are not specialized for nutrients absorption. Buccal dose forms have often been found to show the same bioavailability as intravenous formulations, without the need for aseptic preparations. 2. Bioavailability: Absorption of drugs via the oral route can avoid first-pass organs such as the intestine, liver, and lung (Pang, 2003). 3. Actives can be incorporated into consumer-friendly formats (confectionery products), which may help in masking the taste of some objectionable actives.

Disadvantages of Oral Route Delivery Despite the role of oral mucosa in transporting nutrients and actives, several structural problems hinder the delivery of active substances across the oral mucosa. 1. Compared to the intestinal lining, the oral cavity occupies a very small surface area (2–5 cm2). 2. Buccal cavity, like the entire alimentary canal, is a lipoidal barrier to the passage of active substances. Active transport, pinocytosis, and passage through aqueous pores play only insignificant roles in moving actives across the oral mucosa; hence the majority of absorption is passive and only lipophilic molecules are well absorbed. Polar actives, that is, those ionized at the pH of the mouth (6.2–7.4), are poorly absorbed. 3. Little intercellular absorption is possible across the cuboid squamous epithelium of the oral cavity. However, some amino acids such as glutamic acid and lysine and some Table 8.2. Blood flow (ml/min/100 cc) in various regions of the oral mucosa of the rhesus monkey (Veillard et al., 1987 with permission) Region of oral mucosa Buccal tissue Sublingual floor of mouth Sublingual ventral tongue Gingival tissue Palatal tissue

Blood flow (ml/min/100 cc) 2.4 0.97 1.17 1.47 0.89



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vitamins such as L-ascorbic acid, nicotinic acid, and thiamine are transported via a carriermediated process. 4. Dose form must be kept in place while absorption is occurring since excessive salivary flow may wash the substances away.

Dosage Formulation: Physicochemical Properties of the Active and Dosage A further issue affecting the absorption of orally administered actives is their physicochemical properties. Most of these actives are presented in the form of tablets or capsules so in order to be absorbed, the carriers have to be disintegrated or dissolved. A variety of factors affect the dissolution rate and therefore the availability of the actives for absorption. Product characteristics include format (tablet, lozenge, chewing gum, edible strips, capsule), particle-size distribution of the active, dosage porosity, and presence/absence of coatings.

Chewing Gums Compared to other confectionery formats, chewing gums provide the most hospitable environment for encapsulated and unencapsulated ingredients due to the mild preparation conditions, mainly the absence of heat stress or excess moisture. In addition, the physicochemical properties of gum base can be used effectively to delay/sustain the release of actives. There is no monograph about chewing gum in any pharmacopoeia, but it is described in guidelines for pharmaceutical dosage forms issued by the Commission of the European Communities (1991) as a “solid preparation with a basis consisting of gum which should be chewed and not swallowed, providing a slow steady release of the medicine contained.” Controlling the release of flavors and active ingredients from chewing gums can best be accomplished by a thorough understanding of the complex chemistry of gum bases and their binding affinity to those ingredients.

Typical Chewing Gum Composition and Manufacturing Chewing Gum Composition Chewing gum preparations involve gum base and nonbase components (flavor, sweeteners, color, etc.). Optional ingredients include vitamins, cooling and warming agents, menthol, and other active ingredients. A typical chewing gum formulation is shown in Table 8.3. Table 8.3.

Typical composition of chewing gum formulation

Component Gum base Glucose syrup 45° Mannitol Powdered sugar (to make 100%) Liquid sorbitol 70% Flavor Color Salvage Glycerin

Sugared

Sugar-free

18% 19%

22–30% — 0–5% — 15–22% 1–1.5% 0.1% 5% 1–6%

1.0% 0.1% 5% 2%

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Gum base formulations are usually held as trade secrets by confectionery manufacturers; due to the competitive nature of the chewing gum business, most chewing gum companies have established their own gum base manufacturing factories. Several categories of gum bases can be distinguished, depending on the ultimate application. Gum bases are primarily made up of hydrophilic and hydrophobic polymers (styrene-butadiene elastomers, polyvinylacetates (PVA), waxes, elastomer plasticizers, waxes, fats, oils, softeners, emulsifiers, fillers, texturizers (talc, calcium carbonate), hydrogenated soybean oil, sugar, glycerin, flavors, color, antioxidants, and other minor ingredients. Gum bases are notorious for their affinity to most flavors, thus complicating their release from the chewing gum matrix. A new category of ingredients referred to as sensates has recently been introduced into chewing gums and other confectionery products to provide unique trigeminal sensation of cooling, warming, tingle, etc. When combined with flavors, cooling agents such as N-ethyl-p-menthane-3-carboxamide, N,2,3-trimethyl-2-isopropyl-butanamide, menthyl glutarate, menthyl lactate, isopulegol, menthone glyceryl ketal, and others have been found to enhance the pleasant perception of flavors and breath freshening (Johnson et al., 2004; Wolf et al., 2005). Similarly, warming/heating agents such as capsicum oleoresin, cinnamic aldehyde, pepper oleoresin, gingerol, shoagol, etc. are often used to provide unique warming sensation in the mouth and the trigeminal area. Chewing Gum Manufacture Gum base is softened or melted (50–70°C) and placed in a kettle/mixer fitted with z-shaped blades for 10–30 minutes. Powdered sweeteners, syrups, active ingredients are added following accurate time schedule. Late in the mixing procedure, flavors and cooling/warming agents are then added and the mixture is cooled to 35–45°C, rolled onto plates, scored into strips, and cut into pieces to produce sticks or tablets. Recently, extruders have been introduced for manufacturing chewing gums due to the efficiency, process flexibility, and costeffectiveness of such units. Coating is an essential step in finishing pellet gums and where flavors, colors, and actives can be added. Sugar syrup, gum arabic, starches, and other binders are applied to the surface of gum pellets placed in rotating basket-type mixing/coating units. Tumbling continues until sufficient amounts of coating material are applied followed by gentle polishing to provide smooth surface free of imperfections. A variety of ingredients such as waxes, shellac, talc, and emulsifiers can be used in chewing gum polishing applications. Coated chewing gums are hardened in the 8 weeks following preparation; the coating sugars and polyols (sorbitol and xylitol) develop crystals that provide hardness and crunchy texture. Crystallization, however, creates a porous coating structure with multiple microchannels. The latter can allow migration of moisture and oxygen, thus exposing labile actives to possible losses or degradation reactions.

Chewing Gums for Delivering Flavors and Nonmedicated Actives Significant advances in delivering unique flavors and sensations via chewing gums have been documented in the patent literature. Most of these patents have been filed in the last decade by gum manufacturers and flavor houses who have been keen on adapting their delivery systems technologies to this highly profitable sector of the confectionery business.



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Loss of flavor, either due to degradation from the product or due to its tight binding to the gum base, remains the most challenging concern in chewing gum manufacture. Several approaches have surfaced recently for addressing this problem either directly by (i) accelerating flavor release (burst effect) or indirectly (ii) by enhancing flavor perception via extending the release of physiological cooling agents or sweeteners throughout the product’s normal chewing time. Encapsulated flavors prepared by coacervation, particle coating, entrapping into liposomes or amorphous matrices can be simply applied to the outer coating of chewing gums. For burst-release effect, it is advisable to entrap flavor components into a water-soluble matrix so that flavor release can take place instantly as the product is placed in the mouth (Clark and Shen, 2004). The following citations represent a group of controlled-release applications of chewing gums designed for local delivery of flavors, sweeteners, breath-fresheners, etc. A two-step process for controlling the release of flavors from a chewing gum system was devised by Merritt et al. (1985), where the flavors were incorporated into an emulsion via a hydrophilic matrix. The latter is further dried and ground to appropriate particle size followed by coating with a water-impermeable substance (matrix-reservoir combination systems). Song and Courtwright (1992) patented a method for manufacturing sustained flavor releasing structures. The inventive process comprised of blending the flavors and binding material such as amorphous silicon dioxide hydrates and further coating the compositions with a barrier material such as polyvinylpyrrolidone (PVP). The amount of flavor released was claimed to be about 20% during 20 min. of chewing compared to 35% in a conventional chewing gum. Sustained flavor release was claimed for a process whereby the flavor is partitioned into a water-soluble phase of the gum for immediate release, while the delayed effect was provided by the other flavor portion embedded into the water-insoluble fraction such as polyethylene or polypropylene (Rutherford et al., 1992). Song and Copper (1992) disclosed an innovative approach to controlled release via a fiber structure using melt-spinning technique, which was followed by stretching via applying a draw or a stretching force. The flavor droplets exposed along the sides of the fiber can be released as the solvent infuses into the fiber creating channel-like structures. The length of these channels gradually increases as the active agent directly in contact with the solvent is dissolved. The fiber structures can be incorporated directly into a chewing gum where the pressure generated from chewing will flatten, stretch, and deform the fibers exposing new surface areas of active to the solvent. Wolf et al. (2005) patented a composition for extending the perception of breathfreshening in a chewing gum by encapsulating physiological cooling compounds into the gum matrix. Monitoring breath-freshening using trained sensory panel showed a significant increase in perceived breath freshening intensity compared to unencapsulated control (Figure 8.5). McGrew et al. (2006) formulated a chewing gum containing metal salt, which is claimed to reduce/eliminate oral malodors associated with bad breath. The controlled release of Zn lactate and Cu gluconate claimed to provide breath-freshening benefits by binding to volatile sulfur compounds generated in the GIT that are commonly associated with bad breath. Manufacturing good-tasting sugar-free chewing gums can be a challenging task because of several factors, for instance incompatibility of artificial sweeteners with other components of the chewing gum system. Aspartame (APM) is a methyl ester of L-aspartyl-Lphenylalanine dipeptide molecule, which exhibits about 180 times the sweetening ability of

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Perceived breath freshness (intensity)

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10 9 8 7 6 5 4 3 2 1 0

Encapsulated cooling agents

Control

0

5

10

15

20

Time (min.)

Figure 8.5. Perceived breath freshening intensity of chewing gum containing encapsulated cooling agents and control (reproduced from Wolf et al., 2005).

Figure 8.6. Effect of acids and gelatin on aspartame (APM) retention (reproduced from Bunzeck and Urnezis, 1993).

sugar on an equal weight basis. APM can be destabilized and its sweetening power can be significantly reduced in the presence of aldehyde-based flavors such as cinnamon resulting in chewing gums with unacceptable taste, color, and texture. Similarly, APM can degrade quickly in chewing gums containing sodium pyrophosphate. The latter is added to chewing gum systems to provide teeth remineralization benefits. Bunczek and Urnezis (1993) patented a method for stabilizing APM in cinnamonflavored chewing gums by mixing an aqueous solution of APM with hydrochloric acid and a thickener (gelatin) followed by air-drying and grinding and further incorporation into a chewing gum formula (Figure 8.6). Stability of acid-treated APM with or without gelatin coating was found to be superior to the native untreated sweetener. Acesulfame-K (Ace-K) is another sweetener that can be encapsulated to extend its release throughout chewing. Broderick and Record (1992) developed water-insoluble porous beads that comprised a copolymer of divinylbenzene and styrene impregnated with Ace-K. The beads were further coated with hydroxypropylmethylcellulsoe (HPMC) prior to incorporation into a chewing



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gum system. Release of Ace-K and spearmint was found to be about 40% after 5 min. of chewing compared to 80% from control. Other interesting controlled release systems have been documented in the patent literature such as those proposed by Johnson and Yatka (2000), Ream et al. (2003), Savage et al. (2002), Sharma and Yang (1986), Song et al. (1992) and many others.

Chewing Gum for Delivering Caffeine Caffeine is a well-known stimulant, which is used to alleviate the effects of sleep deprivation and combat headache and fatigue. The caffeine molecule is completely metabolized by the liver, its rate of inactivation is unaffected by the delivery to the liver and can only be modified by a change in hepatic enzyme activity. Incorporating caffeine into beverages and other food products has been very challenging due to many constraints—mainly its aqueous insolubility (2.1%), objectionable bitterness as well as delayed stimulant activity. Syed et al. (2005) studied the pharmacokinetics of three doses (50, 100 and 200 mg) of caffeine delivered via Stay Alert® chewing gum and proposed a dose-proportionate linear increase in plasma caffeine levels. Their study showed that delivering caffeine via chewing gums is an effective and convenient means of maintaining desirable levels of alertness and performance in sleep-deprived individuals. The same chewing gum (Stay Alert®) was also used earlier by another research group (Kamimori et al., 2002) to compare the bioavailability of caffeine delivered via a chewing gum and a capsule. Mean plasma Tmax for individuals who chewed the gum was found to be in the range 44.2–80.4 min. compared to 84.0–120.0 min. for the capsule group, indicating an early onset of pharmacological effect and a faster rate of absorption of the caffeine molecule via the buccal mucosa. Enhancing buccal absorption of caffeine was attempted both in vivo and in vitro. Donbrow and Freidman (1974) investigated the release properties of caffeine using a diffusion cell and concluded that diffusion of caffeine via an ethyl cellulose cell was timedependent, that is, the diffusion follows a zero-order mechanism. Increasing membrane hydrophilicity by incorporating 40% polyethylene glycol (PEG) demonstrated the possibility of enhancing permeability of the caffeine molecule (Table 8.4). An in vitro study by Nicolazzo et al. (2003) showed that pretreating porcine buccal mucosa with different levels of sodium dodecyl sulfate (SDS) (0.05, 0.1, and 1%) significantly enhanced caffeine flux by a factor of 1.57, 1.63, and 1.81% respectively. Gudas et al. (2000) developed a chewing gum containing slow-releasing caffeine profile by pre-encapsulating the active (50–100 mg caffeine) into a water-soluble matrix. Controlled release of small amounts of caffeine over a longer period of time was designed to reduce the impact on taste. Results from the corresponding clinical trials conducted using 6 subjects showed enhanced absorption rate constant (Ka ) when caffeine was administered through the chewing gum due to high buccal absorption rate and subsequent fast delivery into the systemic circulation. A similar change in the onset of dynamic response was noted, for example alertness and performance when caffeine was incorporated at 50–500 milligrams levels. Plasma caffeine concentration was also found to be significantly greater for gum than caffeinated cola or other beverages within the first 10–30 min. after caffeine intake, that is, faster uptake by the body. Ream et al. (2001) formulated a chewing gum for delivering caffeine by layering the active onto the outer shell of the pellet coating. Their study demonstrated significant levels of buccal absorption presumably due to pressure development in the buccal cavity, a result

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Table 8.4. Transfer rate of caffeine as a function of film thickness, caffeine concentration and PEG concentration in film (Donbrow and Freidman, 1974 with permission) Film thickness (cm 104) 26.8 32.7 48.0 Concentration of caffeine (mol 108 l 1) 1.03 2.06 4.12 Concentration of PEG in film (% w/w) 0 10 20 40 50

Rate of transfer reciprocal (mol s1 109)

Rate of transfer/film thickness (mol cm s1 107)

400 3.32 2.20

1.07 1.08 1.06 Rate of transfer/caffeine concentration (l s1 107) 0.505 0.509 0.509 Rate of transfer/PEG concentration (mol s1 109) — 0.115 0.103 0.111 0.108

0.52 1.06 2.10

0.123 1.15 2.06 4.45 5.40

of continued chewing, which may have forced the permeation of the released caffeine molecules through the mucosa.

Chewing Gums for Delivering Vitamins The release of ascorbic acid from chewing gum formulations was investigated by several groups. Ascorbic acid mixed with hydrophobic components has been shown to exhibit a slower but complete release of the drug within 15 min., compared to mixing with hydrophilic ones (Odumusu and Wilson, 1977; Sadoogh-Abasian and Evered, 1979). A slightly faster release of L-() ascorbic acid was observed in vivo compared to its in vitro release in a mastication machine; however, a good correlation was observed between the in vivo and in vitro release patterns within the first 5 min. of mastication. Andersen (2004) incorporated vitamin C into a chewing gum formulation at two different gum base levels (30 and 45%) and showed a very high level of vitamin recovery especially in the 30% gum base formulation. Sadoogh-Abasian and Evered (1979) and Stevenson (1974) independently studied the transport of ascorbic acid across the human mucosal membranes and showed that its absorption is Na ion-dependent. Calcium ions were also found to increase ascorbic acid absorption presumably due to a secondary effect of Na ion fluxes. Buccal mucosa was found to be permeable to dehydroascorbic acid and D-isoascorbic acid. The presence of D-glucose and 3-O-methyl-D-glucose increased the absorption of ascorbic acid but D-fructose had little effect and D-mannitol had no effect. The impact of ascorbic acid solubility and its ionization behavior on the vitamin buccal permeability were also studied by changing pH of the medium stepwise from 3.4 to 9.0. Increasing pH resulted in a gradual decrease in buccal absorption of the vitamin. Vitamin C is only 13.7% ionized at pH 3.4 but almost fully ionized at pH 9.0, thus indicating passive diffusion of the molecule (Odumusu and Wilson, 1977). The process was reported to be not stereospecific since both the natural form L-ascorbic acid and the unnatural D-isomer were transferred across buccal mucosa at similar rates. Glucose was also found to enhance transfer



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of ascorbic acid across buccal membranes, though the effect may be due to glucose acting as an energy metabolite (Stevenson, 1974). Nicotinic acid and nicotinamide displayed similar buccal absorption rates. The latter were also consistent with those determined across intestinal mucosa (Evered et al., 1980). Despite the differences in their ionization behavior at pH 6.0 (nicotinic acid is 6% unionized while nicotinamide is almost fully ionized), both forms of the vitamin are soluble in water and poorly soluble in lipids. Isonicotinic acid and nicotinic acid have identical molecular weights and very similar pKa values (4.84 and 4.77, respectively), yet the former showed a lower rate of absorption suggesting a carrier-mediated transport system (i.e. facilitated diffusion). These studies revealed for the first time that human buccal mucosa is permeable to the water-soluble vitamin, thiamine, as with ascorbic acid (Sadoogh-Abasian and Evered, 1979), nicotinic acid and nicotinamide (Evered et al., 1980) showing some similarities to absorption from mammalian small intestine (Evered et al., 1980).

Chewing Gums for Delivering Antimicrobial Agents Epigallocatechin gallate (ECGC) has been studied for its potential benefits in reducing the risk of heart disease and cancer as well as weight loss. However, recent information from the Tearrow Co. suggests that tea extracts of Camellia sinesis incorporated into chewing gum can permeate the mucosal barriers to help in treating gingivitis and eliminating microbial growth in the oral area (Gelski, 2006). Miconazole is a well-known oral care antimicrobial active. Attempts to incorporate miconazole directly into chewing gums were not very successful due to its strong binding to the gum base. To promote its release, different solid dispersions of miconazole in PEG 6000, PVP 40,000 and xylitol were tested. Dissolution rate data showed that dispersions of miconazole:PEG 6000 (1:4) had the highest level of release from a chewing gum (15-times compared to pure miconazole) due to enhanced aqueous solubility of the active. Addition of lecithin to the miconazole–PEG chewing gum formulation was found to enhance the release rate as well as the time of release both in vitro and in vivo. Lecithin may have improved miconazole solubility by virtue of its ability to form liposomes in aqueous media (Pedersen and Rassig, 1990). In vitro data using a mastication device of Christup and Møller (1986) correlated well with the in vivo data derived from six healthy volunteers. Release of miconazole was also shown to be significantly facilitated by the addition of Panodan 165 (acidic surfactant) to a chewing gum formulation. High surface activity of Panodan 165 as well as its low pH may have increased the solubility of miconazole and/or enhanced saliva absorption into the chewing gum during mastication. Using a panel of five subjects, Witzel et al. (1980) investigated the in vivo release of nystatin, a slightly soluble antifungal agent from chewing gum. Coating the antifungal agent with gum arabic resulted in 24% release of the nystatin compared to only 4% from uncoated nystatin. Despite the enhanced solubility of nystatin using enhancers such as Cremophor RH40, Tween 60 (nonionic surfactants) and Panodan AB 90, in vitro release rate was too fast to provide any significant antifungal effect (up to 99% in the first 10 min. of administration). Lombardy et al. (2001) disclosed an oral hygiene plaque-disrupting chewing gum comprising a core containing encapsulated sodium bicarbonate, which is surrounded by a coating that contains an encapsulated edible acid. Upon chewing and subsequent effervescence development, the formed foam penetrates between the teeth and gum crevices to loosen plaque build up.

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Chewing Gums as Delivery Systems for Oral Health Tooth decay is mainly caused by Streptococcus mutans metabolizing fermentable carbohydrates leading to a drop in pH in the tooth and plaque microenvironment and to gradual dissolution of the hydroxyapatite [calcium phosphate hydroxide, Ca10 (PO4)6(OH)2], the primary component of tooth enamel. Natural remineralization process involves, in part, the flow of saliva (saturated with calcium and phosphate) that raises the pH so that the calcium and phosphate ions can precipitate to replace the dissolved hydroxyapatite. However, this process is very inefficient in most individuals. Sugar-free chewing gums have been promoted for their effectiveness in preventing dental caries. Based on clinical trials, it was suggested that mastication of xylitol-based chewing gum may reduce dental caries in children and young adults better than any other sugar-free chewing gum. This improvement has been associated with reduced levels of Streptococcus mutans and Lactobacilli in saliva along with a reduction in plaque build up at neutral pH (Assev and Rølla, 1986; Wennerholm and Emilson, 1989). However, S. mutans may develop resistance to xylitol after few months of chewing. The effect of chewing nonmedicated chewing gums on plaque pH, saliva flow rates and the incidence of dental caries have been the topic of many studies. Different brands of sugarfree chewing gums claim to stimulate saliva flow rate compared to that of unstimulated saliva flow rate. Peak salivary flow rates are known to develop within the first minute of chewing. Leach et al. (1989) presented evidence for the remineralization of artificial caries-like lesions in human teeth enamel in situ following mastication of a sorbitol-containing chewing gum. Winston and Usen (2002) patented a confectionery composition containing soluble phosphate and calcium salts that are claimed to help remineralize teeth surface lesions and exposed dentin tubules. The composition was described to be applicable to hard candies, chewing gums, lozenges as well as other formats. Patients with xerostomia (dry mouth) most often show elevated risk of caries. Sugar-free chewing gums have been recommended to patients who still have some capacity to secrete saliva (Jenkins and Edgar, 1989). The saliva produced during mastication can alleviate the risk of caries by reducing plaque pH generally seen in response to a sucrose challenge. To further increase caries prophylactic activity of chewing gum, addition of an acid-neutralizing agent (e.g. carbamide) may be appropriate.

Chewing Gum for Delivering Acetylsalicylic Acid The high clearance drug salicylamide has been used as a model substance in chewing gum experiments (Christup et al., 1988b). The bioavailability of acetylsalicylic acid from Aspergum® has been compared to the bioavailability of acetylsalicylic acid from pre-oral tablets. The rate of absorption was shown to be faster from chewing gum than from the tablets and it was concluded that chewing gum might provide a faster relief of pain (Woodford and Lesko, 1981). These results were speculated to be due to a reduction in drug metabolism in the GIT and the liver. Christup and co-workers (1990, 1988) studied the in vitro and in vivo release of different salicylamide chewing gum formulations and showed higher release from the formulation containing less gum base. Micronized salicylamide in a chewing gum showed greater release from hydrophilic formulations compared to their hydrophobic counterparts when the



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gum was chewed for 30 min. (Christup et al., 1988). The release of coarse salicylamide particles from a chewing gum composition was reported to be limited, but was doubled when the active was micronized. These studies suggest that drug release from chewing gum can be modified through formulation or manufacturing processes either by the addition of substances to the gum base which exhibit different lipophilic or hydrophilic characteristics or by modifying the physical characteristics of the incorporated drug.

Comparison of Delivery Profiles between Chewing Gum and Lozenge Christup et al. (1990) used gamma-scintigraphy to examine how effectively drugs were released in vivo from chewing gum, their distribution profile once released and the length of time drug remained in the oral cavity following release. Release profile from chewing gum was compared to those observed following the administration of lozenges and sublingual tablets. Vitamin C was found to be absorbed better from a chewing gum than from a tablet (Christup et al., 1988) Non-absorbable, water-soluble compound Tc E-HIDA (N-(N-(2,6-dimethylphenyl)) carbamoylmethyl iminoacetic acid) used as a model active showed complete release after 10 min. of chewing at a rate of 1 chew/sec. Activity (counts) vs. time (min) profiles of the oral cavity and the stomach of six subjects following administration of the 3 different dosage forms (chewing gum, lozenge and sublingual tablet), did not show any difference in the distribution of Tc-HIDA within the oral cavity, glottis or upper oesophagus. However, Tc E-HIDA released from sublingual tablets remained for the longest time while Tc E-HIDA released from lozenges remained for the shortest period in the oral cavity (Rassing, 1994).

Lozenges (Hard Boiled Confections) Lozenges have long been used as vehicles for delivering medicaments to alleviate cold symptoms such as decongestion, to soothe sore throats and clear nasal passages. Such medicaments include analgesics, antitussives, expectorants, cooling, warming, numbing and tingle agents. Lozenges are essentially hard-boiled candies that can be formulated in sugared and sugar-free versions. Lozenge manufacture involves heating a glucose/sucrose mixture to evaporate water and transform the matrix from a crystalline to an amorphous glassy phase. Lozenges can be manufactured using batch or continuous processes. Essential additives include acids, flavors and colors while therapeutic additives include actives such as menthol, benzocaine, dextromethorphan, pectin, vitamins or other nutrients. Lozenge manufacture exposes these actives to harsh moisture and heat environments and often results in partial or total degradation of heat-labile components.

Lozenges for Delivering Flavors and Sensates Release of actives from a lozenge is activated by sucking and gradual dissolution of the sugar (or sugarless) matrix. Menthol released from lozenges, for example, can bind to thermo-receptors located within the free nerve endings of the trigeminal and nasal cavities. The resulting cooling sensations are presumed to provide analgesic effects via modulating the sensitivity of cutaneous pain fibers.

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Due to their water-based nature, lozenges can be most effective in providing “burst release” of flavors, sensates or other actives. Their hydrophilicity makes them ideal permeability enhancers for hydrophobic actives (e.g. cooling compounds) across membranes of the oral area. Incorporating encapsulated particulates into lozenge formulations results most often in premature destruction of the capsule and the release of entrapped substances during processing and before consumption. Micelles and emulsion-based carrier systems are, generally speaking, better suited for lozenge formulations. An effective “burst” release approach was developed by Clark and Shen (2004) whereby encapsulated particulates or powders were layered onto the lozenge outer surface to provide quick dissolving matrix to liberate the entrapped flavor components. Rivier (2005) patented a lozenge-based delivery system to provide “burst” release of a solid active nestled into the center of an oval-shaped lozenge. Due to the inherently thin walls at the ends of the larger diameter of the oval piece, “burst release” is activated by sucking the lozenge and creating channels for quick diffusion of the active. A wide range of actives can be incorporated into this lozenge design including flavors and sensates for refreshment. A unique type of actives that can be dosed into the center of the oval piece is polyols. By virtue of their negative heat of dissolution in particular xylitol and eryhthritol, their release and high solubility in the saliva can provide a refreshing moist cooling sensation. Therapeutic actives such as analgesics can be also employed to provide quick relief.

Lozenges for Delivering Throat Relief Actives Despite these advantages, sugar- or polyol-based lozenges do not adequately provide long-lasting solutions to problems unique to the mouth and the esophageal area due to the quick dissolution, short residence time and mode of lozenge consumption, that is, moving around in the mouth and saliva stimulation that can be secreted and swallowed. A recent trend in lozenge formulations involves incorporating high molecular weight polymers with mucoadhesive properties into sugared/sugar-free formulations. This practice is supported by the USP monograph permitting the use of mucoadhesive materials (referred to as demulcents) for providing relief from mucus irritation, pain and discomfort associated with laryngopharyngitis (sore throat) and other upper respiratory tract infections. Examples of these demulcents include gelatin, pectin, celluloses, and alginates. Other types of nonpolymerbased mucoadhesive agents include titanium and silicon dioxide (Dobrozsi, 2003) and lipid vesicles (Bealin-Kelley et al., 2002). Lozenges formulated with demulcents, however, are bland tasting and are often perceived by consumers as nonefficacious. A new generation of lozenges has been formulated with sensates (cooling or warming compounds) to provide an additional sensory cue of soothing. Coincidentally, it was discovered that combining demulcents with sensates can extend the perceived soothing warmth from the mouth to the throat (Figure 8.7), an attribute that is highly desirable by consumers (Bealin-Kelley et al., 2002; Lakkis, 2006).

Lozenges as Delivery Systems for Dry Mouth Relief Lozenges have also been formulated to provide relief from dry mouth symptoms referred to as xerostomia. Wolfson (2002) patented a composition using Heliopsis longipes root for



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time, min 4 8

1

3 2 1

7

2

0.3% pectin

0

0.2% pectin 6

3

5

4

0.1% pectin

Figure 8.7. Effect of pectin level (0.1, 0.2 and 0.3%) on perceived warming in the human throat. Sensory panel ratings scale ranged from 0 (very low warming intensity) to 4 (highest warming intensity). Graph reproduced from Lakkis (2006 with permission).

increasing salivation, thus alleviating dry mouth feeling while maintaining oral hygiene. Tutuncu et al. (2003) developed a food acid-containing lozenge, which claimed mouth moistening benefits. Kayane et al. (2003) described a throat care lozenge, which promotes the secretion of mucin to provide bactericidal effect by inhibiting the adhesion of pathogenic bacteria, Pseudomonas aeruginosa, Haemophilus influenzae, or Staphylococcus aureus. Efficacy of the lozenge was confirmed via ELISA testing, which showed increased levels of IgA and lysozyme content in the mucus secretion.

Lozenges as Delivery Systems for Teeth Remineralization Actives Calcium phosphate, the main component of dentin and teeth enamel, while insoluble at neutral saliva pH, is readily soluble in acidic media generated by fermentation of ingested carbohydrates. To alleviate the impact of these events and slow down the development of caries and lesions, it is desirable to increase the available concentration of calcium and phosphate ions in the oral cavity to speed up the remineralization process. Several inventions and commercially available confectionery products (lozenges and chewing gums) that claim teeth remineralization are commercially available (Chow and Takagi, 2001; Kaufmann, 2003; Mazurek et al., 2000; Savage et al., 2002; Winston and Usen, 2002). One drawback with using calcium- and phosphate-containing salts and buffers in hard-boiled lozenges is the development of bitterness and grittiness due to complexation of the calcium and phosphate ions in the candy matrix. One approach to overcome these drawbacks is to skillfully incorporate these actives into separate components of the candy matrix so that the actives can be released concurrently in their soluble forms to form the hydroxyapatite in the generated saliva (Lakkis and Wong, 2007).

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Bioerodible and Bioadhesive Devices This category encompasses a wide range of weak and strong adhering structures that are commercially available in the form of films/strips, patches, tablets or other devices. Weak adhesion is desirable for breath freshening and flavor delivery films while strong adhesion is critical for medicated applications (e.g., antimicrobials and teeth whitening strips). Bioadhesive and bioerodible devices represent an ideal delivery system due to many attributes such as (i) ease of consumption by individuals having difficulties in swallowing, (ii) localization in specified regions of the oral or other GIT sites to improve and enhance the bioavailability of actives, (iii) optimum contact with the absorbing surface to permit modification of tissue permeability, (iv) reduced need for drug overage and (v) avoidance of first-pass metabolism. Mucoadhesion takes place by establishing an adhesive bond between the device and the mucus membranes resulting in a reduced total surface energy of the system because two free surfaces are replaced by one (Anlar et al., 1984; Guo, 1994). Polymers with hydrophilic moieties such as carboxyl and hydroxyl groups can bind to the sialic acid and other oligosaccharide residues in the mucosal membranes. The process takes place in three stages: hydration, interpenetration, and mechanical interlocking between mucus and the polymer. Mucoadhesive strength is affected by various factors such as molecular weight of the polymer, its swelling power, size and configuration of the device, time of contact with the mucus, and the physiological nature of the membrane. Generally, oral bioadhesive and bioerodible devices can be designed to adhere to the cheek (buccal area), the floor of the mouth (sublingual tissue), gums surrounding the teeth, and the roof of the mouth (palate tissue). Efficacy of mucoadhesive and bioerodible devices is well documented in many pharmaceutical and consumer health applications. Examples include teeth-whitening, accelerated healing of inflamed or damaged tissues, prolonged and improved coating and protection of the mouth and esophagus (Barklow et al., 2002; Choi and Kim, 2000), sustained release of insulin in the stomach via mucoadhesive microspheres of glizpide, which is a second-generation sulfonylurea used to acutely lower blood glucose levels (Kahn and Shechter, 1991). Confectionery-based devices are available in the form of medicated and nonmedicated films commonly referred to as edible strips. The latter are usually of the size of a postal stamp, which is placed on the tongue to deliver flavors, breath-fresheners, decongestants, etc. Popularity of these films has soared recently with the introduction of Listerine® pocketpaks™ by Pfizer, Eclipse® Flash by Wrigley’s and most recently Theraflu® cough relief strips by Novartis, Inc. A wide variety of water-soluble and/or -insoluble food-grade hydrogels has been used in formulating edible strips. The choice of a suitable composition depends largely on desired functionality and residence time in the oral cavity, its solubility, type of active, and required payload. Typical edible-strips formulations comprise a combination of film-forming polymers, fillers, plasticizers, colors, and actives (menthol, flavor, cooling/warming compounds, vitamins, analgesics, etc.). Polymers such as pullulan are favored for their film forming properties and excellent solubility and clean aftertaste (no residual gumminess). Manufacturing films with pure pullulans, however, has been hindered by its weak mucoadhesive properties and cost. Mucoadhesion of pullulans may be improved by incorporating several additives such as PEO, mono- or oligosaccharides to the strip formulation (Ozaki and



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Miyake, 1995). Alternative economical film materials have been proposed such as celluloses, glucans, native, and modified starches. Edible strips manufacture involves forming a hot, stable aqueous solution of the film polymer and the active(s), casting the solution over a conditioned belt followed by heat drying and cutting into desired strip dimensions. Such conditions may degrade heat and moisture labile actives. Encapsulating actives (e.g., food acids) prior to their incorporation into film formulation may help retard their degradation and help maintain the film integrity (Virgallito and Zhang, 2006). In vivo assessment of release mechanisms from mucoadhesive devices has been hindered by physiological variables such as amounts and physicochemical properties of human saliva and movement of the device in the mouth. Most investigations indicate that the release from mucoadhesive devices takes place via erosion, diffusion, or a combination of both. Critical factors that can have profound impact on release from bioadhesive/bioerodible devices can be summarized as follows: 1. Film physicochemical properties, mainly active payload, film forming polymer chemistry, its thickness and solubility (addition of maltodextrin to pullulan films can enhance their dissolution and release of the active). 2. Although high viscosity polymers can improve the bioadhesion of films, at very high viscosity, nonhomogeneous distribution of the active may result in unpredictable drug release rates (Wong et al., 1999). 3. Location of the device in the mouth as well as tongue movements can play a crucial role in the device’s residence time and the active’s release rate/mechanism. De Vries et al. (1991) showed that application of buccal patch to the palate provided longer adhesion than that of the cheek mucosa. Bouckaert et al. (1993) compared the adhesion of miconazole mucoadhesive tablet to the gingival, palatal, and cheek mucosa and concluded that the longest adhesion was in the gingival area while the shortest was at the cheeks. When applied to the cheek, the tablet is lodged very near the parotid duct, thus the adhesion time might be reduced by the salivary flow. Subsequently, the polymer mixture may swell more rapidly and the tablet will become prone to erosion. Despite the fact that less saliva is present in the palatal and gingival mucosa compared to the buccal mucosa, adhesion time for the palate was comparable to that for the cheek and significantly lower than the gingival. 4. Excessive matrix swelling, such as the case with native starch, can hinder the controlled release of actives. Tuovinen et al. (2003) using two small model molecules (sotalol, m. wt. 308 and timolol m. wt. 332) and two large model molecules (FITC dextran, m. wt. 4400 and BSA m. wt. 68,000) showed that the small molecules, solatol, and timolol were released more rapidly than the FITC dextran and BSA from a native potato starch matrix (PBS buffer pH 7.4 with or without α-amylase) due to excessive starch swelling. Release of the small molecules was continuous whereas the release of macromolecules showed discontinuities. 5. Hydrophobic/hydrophilic nature of the hydrogel and active also can have a significant impact on the release behavior. Tuovinen et al. (2003) showed that the model molecule, sotalol, was released faster than timolol (more hydrophobic) from a starch acetate film (hydrophobic) demonstrating stronger interaction between the matrix and active. Release of timolol and sotalol was faster than the weight loss of the corresponding film

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Figure 8.8.

Cross-section of a typical seamless capsule showing solid shell and a liquid center.

presumably due to the hydrophobic nature of the starch acetate film, thus providing evidence for erosion-controlled mechanism.

Seamless Capsules Seamless capsules represent a class of delivery systems that can provide powerful impact, but has not yet realized its full potential. Soft seamless capsules are ideal carriers for liquids or a suspension of solids in a liquid. A variety of applications have been documented in the patent literature, including delivery of flavors, menthol, and eucalyptus oil for breathfreshening (Karles et al., 2006; Tanner and Shelley, 1996; Yang, 2005) the pro-vitamin A lycopene (Paetau et al., 1999) and concentrated alcoholic and nonalcoholic beverage concentrates for recreational use (Hutchinson and Garnett, 1999; Sexton and Lakkis, 2003). Ideal seamless capsules are 4–8 mm diameter with a thin shell wall of 300–600 microns and maximum core-to-shell ratio of 9:1 w/w. This ratio represents the highest payload of any encapsulation technology known today. Seamless capsule formulations comprise a liquid center and a solid soft shell. The latter can be made of gelatin, agar, alginates, celluloses, or other gelling (moldable) polymers in combination with suitable plasticizers (Figure 8.8). Seamless capsules are manufactured using specialized machines with coaxial multiple nozzles such as the Spherex system (available from Freund Industrial Co. Japan) as well as other suppliers. The outermost shell layer is formed by extrusion of a hot gelatin solution (60°C) from the outer nozzle and the liquid core (immiscible in water) is extruded from an inner nozzle to form a concentric jet. The jet is further injected into a cooled vegetable oil bath (ca.12°C) to harden the shell. Seamless capsules in the form of spheres are formed due to surface tension. One of the critical attributes of seamless capsules is the shell quality, which is expected to be soft and to dissolve readily in the mouth with no residues. For maximum efficacy and clean aftertaste, release of the active from seamless capsules should take place via breaking



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the sphere without any perceivable swelling. Few challenges, however, can complicate the manufacture of seamless capsules and their functional performance, mainly: 1. Shell–core interactions: Due to the hydrophilicity of the shell material, this technology can only accommodate hydrophobic cores. Hydrophilic substances can interact with the shell material resulting in film plasticization and in some cases can help promote microbial growth, a major concern upon processing and shipping of the capsules. 2. Shell thickness: Readily dissolvable capsules require the formation of a thin shell. Shell thickness can affect capsule diameter, that is, for a constant core to shell-mass ratio, shell thickness increases with increased diameter of the capsule. 3. Shell (polymer viscosity): Desired film properties can be achieved by maintaining a delicate balance among many parameters, mainly between polymer viscosity and shell dissolution in the mouth. Very low viscosity polymers can lead to capsule deformation and crushing while too high viscosity can lead to the formation of satellites extended from the capsule surface. Wonschik et al. (2005) patented a unique shell formulation comprising a mixture of high bloom and hydrolyzed gelatin (zero bloom). The high bloom component is claimed to provide solid network, critical for shell processing while the hydrolyzed gelatin occupies spaces in the formed network to provide rapid dissolution by the saliva. 4. Core Physical properties: For effective processing, liquids, solutions, or suspensions should flow by gravity at room temperature. In general liquids with a wide range of viscosity from 0.2 to >3000 cp at 25°C can be encapsulated. Also, encapsulated liquids must have a pH from 2.5 to 7.5 beyond which the gelatin shell would deteriorate. A new generation of seamless multilayered capsules has been commercialized recently (Jintan Co., Japan) that claims a multitude of functions. Sunohara et al. (2002) patented a multilayered seamless capsule design where the outer shell can provide flavor or breathfreshening and the inner layers can be swallowed to treat stomach-originated bad breath.

Pressed Tablets Pressed tablets include mouth dissolving, fast-dissolving, rapid-melt, porous, orodispersible, and melt-in-mouth products. A wide range of tablets and capsules are commonly used for delivering breath freshening (breath mints) and pharmaceutical actives, although the majority of such tablets are designed to be absorbed in the GIT. Pressed tablets are prepared by dry blending the active ingredients with waterdisintegratable compressible carbohydrate and a binder and then compressing into a convexshaped tablet. Strength/compactness of these tablets can be detrimental to the extent of disintegration, dissolution, and absorption of the active. One of the attractive features of pressed tablets is the possibility of incorporating high levels of actives compared to other dosage formats. Haines (2004) investigated the buccal absorption and bioavailability of vitamin B12 from pressed tablets and a nanofluidized B12 suspension (NF®) via spray applicator as an alternative means to deliver this essential nutrient to patients suffering from intestinal disorders such as celiacs, who cannot absorb this vitamin from food sources. Results from that study showed that nanodroplets provided a more effective vehicle for delivering the active molecule across the mucosal barriers at a faster and more even rate than from the tablet or even the nonprocessed or “normal” vitamin B12 solutions.

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Effervescent Tablets Effervescent tablets can be designed to provide enhanced release in the mouth as well as the lower GIT; Effervescence is the reaction (in water) of acids and alkalis to produce carbon- dioxide. Typical acids used in effervescent tablets are citric, malic, tartaric, adipic, and fumaric while sodium bicarbonate and potassium carbonate are the most commonly used alkalis. Effervescence can help promote calcium absorption in the stomach as well as sustain biological activity of probiotic bacteria (Lee, 2004). It has been speculated that CO2 produced by effervescent reactions induce some alteration (widening) of paracellular pathways, a primary route of absorption of hydrophilic actives (Anderson, 1992; Nuernberg and Brune, 1989). Absorption of hydrophobic species can also be enhanced due to the nonpolar CO2 gas molecules partitioning into the cell membrane to create a hydrophobic environment which allows hydrophobic actives to be absorbed (Eichman, 1997). CO2 may also help absorption by reducing the thickness and viscosity of the mucus layer adjacent to the mucosa (Pather et al., 2002).

Chewable Tablets Most chewable confectionery products are gelatin based. Gelatin is a very reactive surface that interacts with mucin rendering bioavailability very difficult.

Conclusions The oral mucosa responds to the senses of pain, touch, and temperature in addition to its unique sense of taste. Some physiological processes are triggered by sensory input from the mouth such as the initiation of chewing, masticating, swallowing, etc. The most important physiological variable, however, that can markedly affect the release characteristics of an active from a confectionery dosage is whether a person sucks or chews the formulation, since systems designed to be chewed will invariably be sucked and vice versa by some individuals. Chewing gums possess an advantage over other confectionery formats for controlling the release of drugs such as nicotine, caffeine, or other medicinal substances in that if the gum is swallowed, release of the active in the stomach and lower GIT is extremely low; therefore, reducing potential or toxicity. Drugs and actives ingested via the oral route can be designed for either or both of the following: • Local Delivery: Confectionery products have demonstrated their practical effectiveness in delivering flavors, cooling and warming agents, antimicrobials, caries prevention and xerostomia relief agents; and • Systemic Delivery: Nicotine, vitamins, caffeine, salicylic acid are the most common actives that can be embedded in a confectionery matrix and have the potential to be absorbed through the oral mucosa into the circulation, thus giving rise to a systemic effect. Actives absorbed directly via the membranes lining the oral cavity avoid metabolism in the GIT and the first-pass effect of the liver since the oral veins drain directly into the vena cava. Alternatively, actives released from a chewing gum or other confectionery dosage form—but not absorbed through the oral cavity—membranes will be swallowed and enter the stomach in a dissolved or a dispersed form in saliva.



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9

Innovative Applications of Microencapsulation in Food Packaging Murat Ozdemir and Tugba Cevik

Introduction The use of proper packaging materials and methods to minimize food losses to provide safe and wholesome food products has always been the focus of food packaging. In addition, consumer demands for better-quality, fresh-like and convenient products have been intensifying in the last two decades. A wide variety of packaging materials and technologies have been developed to meet these consumer requirements and to limit package-related environmental pollution and disposal problems (Ozdemir and Floros, 2004). Despite these advances and availability of unique materials such as plastics that can be specifically designed to delay adverse effects of the environment on food products and to extend their shelf-life, novel approaches to the development of packaging materials containing microencapsulated active particles have emerged recently. Encapsulation is a technique by which a material or a mixture of several materials can be coated or entrapped in another material. The development of a successful microencapsulated product primarily depends on: 1. selecting an appropriate shell formulation, usually GRAS (generally recognized as safe) materials that are approved by the Food and Drug Administration (FDA) or other international health authorities; 2. selecting an appropriate process to provide the desired functionality, stability, and release mechanism; 3. economic feasibility of large-scale production including capital, operating costs, and other miscellaneous expenses. An appropriate shell formulation must stabilize the core material, must not react with or deteriorate the active agent, yet releases it under specific conditions based on the product application. Polysaccharides, proteins, waxes, fatty acids, gums and their derivatives are common shell materials that are approved for food use. Microencapsulation of food ingredients can be achieved by either physical or chemical methods. Physical methods include extrusion, fluidized bed, spinning disc, and spray drying. Chemical methods include coacervation, gelation, phase separation, and molecular inclusion. Microcapsules can be produced by depositing a thin polymer coating on small solid particles or liquid droplets, or by the process of dispersion of solids in liquids. The core material or the active agent may be released by friction, pressure, diffusion through the polymer wall, dissolution of the polymer wall coating, or by biodegradation.

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Microencapsulated Actives for Packaging Applications Microencapsulation can most often extend the shelf-life of foods while improving their nutritional quality, appearance, and in various instances inhibiting the growth of pathogenic and spoilage microorganisms, thus ensuring food safety. Important examples of microencapsulation in food packaging include incorporation of antimicrobial agents, insect and/or rodent repellents, scented fragrance-inserts and flavor-releasing systems, pigments, inks, and time–temperature indicators.

Antimicrobial Food Packaging Materials Traditional food protection techniques include curing, smoking, or pickling which were primarily effective in changing the moisture content or water activity of the foods. In recent years, more sophisticated preservation methods have been developed to extend shelf-life of foods. Figure 9.1 shows an example of novel microcapsules that can deliver preservatives from plastic films or edible coatings that are currently available. Changing lifestyles and the limited time available for food preparation require an increasing variety of high-quality, safe, nutritious, and convenient food products today. Allyl isothiocyanate is an effective inhibitor against various pathogens, particularly Escherichia coli O157:H7. Consumption of undercooked ground beef has been identified

Plastic film

Active agent released from the microcapsule

Food

Core containing active agent

Microcapsule (a)

Plastic film Edible coating

Food

Active agent released from the microcapsule

Core containing active agent

Microcapsule (b) Figure 9.1.

Migration of active substance from (a) plastic film, and (b) edible coating.


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as one of the main causes of E. coli O157:H7 outbreaks in North America (Waters et al., 1994). Chacon et al. (2006) microencapsulated allyl isothiocyanate in gum acacia and corn oil prior to incorporating the preparation into aseptically treated chopped beef that was inoculated with a known concentration of E. coli O157:H7. The system was packed under nitrogen and stored under refrigeration (4°C). After 18 days, the chopped beef was found to be free of E. coli O157:H7. Similarly, Klein et al. (2004) described a method for microencapsulating actives such as antibacterial and antifungal agents into a variety of polymeric food packaging materials such as polyethylene, polypropylene, polyester, polycarbonate, polyvinyl chloride, and polyvinylidene chloride. These films were described as especially useful for controlling bacteria and fungi on food surfaces. Agar diffusion tests showed that microencapsulated antibacterial agents were effective against Staphylococcus aureus, E. coli, Pseudomonas aerugenosa, and Streptococcus spp. Thomas et al. (2005a, b) patented a method in which an antimicrobial agent was microencapsulated prior to being integrated into the package structure via extrusion. The method was claimed to be effective in providing thermal stability during package processing and manufacturing, but readily released the active agent upon contact with moisture. Avery Dennison Corp. (USA) developed an antimicrobial active label that releases trace amounts of chlorine dioxide (ClO2) gas from the label. Chlorine dioxide is a broad spectrum antimicrobial agent effective against both bacteria and fungi. It can also be used to eliminate odors and retard microbial growth on perishable food products, thus extending their shelf-life. Laboratory tests showed that the inclusion of one small antimicrobial label on the inside of rigid plastic packaging can significantly extend the shelf-life of fresh berries. The time release delivery of the chlorine dioxide is moisture activated. The main advantage of this system is that it does not require direct contact with the food. A promising application of controlled release is in antimicrobial agents incorporated into chewing gums for reducing the growth of microorganisms in the mouth and thereby retarding tooth decay. Barabolak et al. (2005) produced a chewing gum with controlledrelease properties in which the antimicrobial agent (chlorhexidine digluconate) was encapsulated via film coating. Particles containing the encapsulated antimicrobial agent were claimed to be adaptable to produce fast or delayed release when the gum is chewed. Microencapsulating properties of whey proteins have been investigated extensively in recent years (Ozdemir and Floros, 2001; Rosenberg, 1997). Whey protein concentrate and whey protein isolate have been shown to exhibit excellent microencapsulating properties for both volatile and non-volatile core materials (Young et al., 1993a; Lee and Rosenberg, 2000). The high microencapsulation yield of whey proteins is presumed to be a result of their efficient emulsifying capacity, especially in the presence of carbohydrates (Young et al., 1993b). Films and coatings from whey not only degrade more readily than polymeric materials, but also could supplement the nutritional value and improve the sensory attributes of coated foods. Ozdemir and co-workers (Ozdemir, 1999; Ozdemir and Floros, 2001) developed active antimicrobial films made of whey protein isolate, sorbitol, beeswax, and potassium sorbate. The mechanism and release profile of potassium sorbate in these films were found to follow non-Fickian diffusion model. A mathematical model derived from Fick’s second law of diffusion with a time-dependent diffusion coefficient was used to analyze potassium sorbate diffusion. Subsequent analysis showed that diffusion coefficients of potassium sorbate in whey protein films were ten-fold higher than those in edible wheat gluten and low density polyethylene (LDPE) films, and ten-fold lower than those in intermediate moisture foods.

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In a recent study, Ozdemir and Floros (2003) investigated the effect of different constituents (levels of whey protein, plasticizer, wax, lipid, and antimicrobial agent as encapsulant) on the diffusivity of potassium sorbate using mixture response surface methodology. Their study showed that increasing whey protein concentration in the film decreased potassium sorbate diffusivity. Sorbate diffusion increased with increasing sorbitol concentration but decreased with increased concentration of beeswax in the film. A rise in the initial active (potassium sorbate) concentration in the film resulted in higher diffusion coefficients. Strong interactions were observed between beeswax and potassium sorbate, and whey protein and beeswax.

Insect and/or Rodent Repellent Food Packages Insect infestation of produce and food products results in spoilage and subsequent economic losses. Controlling insect infestation has generally been achieved by fumigation with methyl bromide. Methyl bromide is a toxic substance that can adversely affect the human central nervous and respiratory systems if present at high concentrations. Methyl bromide is also known to be a major contributor to the depletion of Earth’s ozone layer. One way to overcome the disadvantages of methyl bromide is to find less toxic and less harmful insect repellents and to incorporate them into packaging materials to form packages with controlled-release properties. Microencapsulation of pesticides, herbicides, and other pest control agents has been an active area of development. Pest control agents are currently microencapsulated to prolong their activity while reducing mammalian toxicity, volatilization losses, phytotoxicity, and environmental degradation. Spector (1981) introduced a low-cost, self-stick tab in which an active agent-saturated pad can be enveloped within a perforated sac which can then be adhered to a desired site to release the active over an extended period of time. The active agent can be an insect or animal repellent or a fragrance (Figure 9.2), and the system can be stuck directly onto food packages or boxes to prevent their infestation by insects and animals. The protection of agricultural products with biopesticides has been promoted recently as a means of reducing the adverse effects of chemical insecticides (Marrone, 1999). Development cost, time and ease of registration, and potential growing markets make biopesticides popular over chemical pesticides (Brar et al., 2006). A number of biopesticides (bacteria, Core containing repellent material

Microcapsule wall

(a)

(b)

Figure 9.2. Description of the action of a system composed of microcapsules containing a repellent material: (a) microcapsule core containing a repellent, and (b) diffusion and evaporation of the repellent material through the wall.



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fungi, virus, pheromones, plant extracts) have been already in use to control various types of insects responsible for the destruction of agricultural crops. Bacillus thuringiensis-based biopesticides are especially important and are estimated to constitute almost 97% of the world biopesticide market (Cannon, 1993). A biological pesticide is effective only if it has a potential major impact on the target pest, market size, cost- effective and is capable of overcoming a number of technological challenges such as fermentation, formulation and delivery systems. Biopesticides have been encapsulated in a coating made of gelatin, starch, cellulose, or other polymers, and even microbial cells (Barnes and Cummings, 1987a, b; Barnes and Edwards, 1989). Bok et al. (1993) showed that encapsulated microbial pesticides possess excellent adhesiveness; therefore, they can be applied directly to the soil or the plant. When the encapsulated biopesticide is embedded into a plastic film, the film can be applied near the roots or cuts of the crops to protect them against pathogens upon storage or during transportation. Another recent advance in encapsulation is the production of hydrocapsules that are water-based shellcores, consisting of a polymer membrane surrounding a liquid center. These shells can be produced using UV radiation-initiated free-radical copolymerization of functionalized prepolymers (silicones, urethanes, epoxys, polyesters, etc.) and/or vinyl monomers such as acrylates for better dispersion and UV radiation protection (LecheltKunze et al., 2000; Toreki et al., 2004). El-Rehim et al. (2005) formulated a polyacrylamide/polyethylene oxide hydrogel to encapsulate and cross-link bioactives such as Atrazine. The active was incorporated into the hydrogel matrix via electron beam irradiation process. Results showed that copolymer blend composition, its gel content, and irradiation dose greatly affected the Atrazine release rate. In addition, Atrazine release rate was found to decrease with increasing pH but increased at high temperatures. Packaged products are also susceptible to infestation by many insects and mites which are capable of perforating the packaging material or use existing holes or openings in the food package for penetration. Rieth et al. (1986) encapsulated 2-heptanone, an insect repellent for bees and other insects, in a polyvinyl chloride–polyvinyl acetate plastic. Jones and Hill (1982) added naphthalene flakes and citronella oil in solid form to synthetic resins such as polyethylene, polypropylene, and polystyrene to form insect- and animal-repellent plastic films. The resultant films were shown to have lower tensile and tear strengths than films made without the actives (insect and animal repellent additives). Atkinson (1991) described a microencapsulation process for manufacturing animalrepellent plastic films where terpenes were incorporated into linear low-density polyethylene (LLDPE) melt via extrusion. Radwan and Allin (1997) developed a controlled release insect repellent device that was described as useful for foods, tobacco, and other consumable items with the active being an essential oil. Navarro et al. (2005) produced a pestimpervious packaging material by combining ar-turmerone, sesquiterpene alcohols, and/or turmeric oleoresin solid residue. These materials were incorporated into plastics, adhesives, or printing inks via microencapsulation.

Scented Fragrance-Inserts and Flavor-Releasing Systems Food packaging materials, particularly plastics, may interact with food flavors, resulting in loss of flavors, known as flavor scalping, therefore the need to replace these lost flavor constituents. Although the use of high-barrier plastics holds food flavors in the package,

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additional flavor-releasing systems may be necessary in some instances, particularly when heat seal layers of a package have high affinity to flavors. In addition, consumers always like to smell pleasing flavors when they first open a food package (Brody, 1992). Flavorreleasing systems are highly popular in the beverage industry, microwavable foods, and coffee makers. The beverage industry, particularly the soft drink segment, is highly competitive. Manufacturers take great care and make substantial efforts to formulate their products in such a way to differentiate them from their competitors’ and to make consumption of the food product more enjoyable for the consumers. In the soft drink industry, despite the high contribution of taste to the overall soft drink experience, its aroma especially when the bottle is first opened is equally important. Ashcraft and Wong (1993) invented a package that releases a burst of flavor when the package is opened. The novel flavor-burst structure comprised a multilayer film with a flavor-carrier layer disposed between the barrier layers. Due to their chemical incompatibility, the flavor agent desorbs from the carrier when one of the barrier layers is removed from the carrier. Sun et al. (2000) developed a flavored polyethylene terephthalate (PET) packaging system where the aroma is released once the bottle cap was opened. Unfortunately, typical microencapsulated materials do not adhere well to PET; thus the surface of PET bottles must be modified before the microencapsulated material is applied to the bottles. A successful way to resolve this problem is by treating the surface with a primer that enables the microencapsulated material to adhere to PET or to roughen the surface using laser etching. The use of overwraps on packages can improve the appearance and maintain the quality of materials within the package. The use of a tear strip having the ability to release fragrance at the time of opening of the package can add further benefit to the overwrap; for example, release of a controlled fragrance can give the impression to the user that the ingredients of the package are fresh. Fraser (1988) described a package that releases a fragrant liquid from microcapsules when a tear strip is removed from the package. In this system, the separation of multilayer sheet materials ruptures the microcapsules fitted to the intermediate adhesive layers and subsequently releases the entrapped fragrance. The described packages can be made of paper, cardboards, polymeric materials, coated paper, foil, composite structures, metallized paper, and so on. In a similar application, Sprinkel and Newsome (1988) microencapsulated an aromatic substance in a cigarette package–overwrap where the aromatic substance is released upon pulling the tear strip. This mechanism was described as useful for releasing aroma of freshness or for adding flavorings to the cigarettes in the package. CSP Technologies (US) developed an aroma emitting and aroma absorbing package in which the active agent was encapsulated within three component plastic system. Disperse Technologies (UK) combined a patented thin film–encapsulating technology with ultraviolet curing technology to produce films and coatings that have controlled-release properties (Wheeler, 2001). These films and coatings were claimed to possess a very long-lasting impact for up to 6 months. Arcade Marketing (based in the United States) commercialized the MicroFragrance label for foods, especially to promote the sales of low calorie cereal bars. MicroFragrance label is printed onto a clear film so that it does not wear down or blend with another smell such as paper. Driscoll Labels (US) customized long-lasting, scratch-and-sniff labels for the fragrance and food industries. This technology allows the consumer to perceive the aroma of the food without opening the package. Scentisphere developed a printable, scented ink known as rub-and-sniff ink that can be printed directly onto packaging materials. The rub-and-sniff ink is claimed to have advantages over the traditional scratch-and-sniff labels since the



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Encapsulated flavors released into the package contents

Encapsulated flavors released into the air Figure 9.3.

Package

Release of microencapsulated flavors from flavor-incorporated plastics.

scented inks can be added to the ink using standard printers without any interruption in the printing process or the inconvenience of having the ink drying quickly. The US-based company ScentSational Technologies™ is a pioneering company in microencapsulated packaging. A schematic of their CompelAroma® flagship technology for encapsulating flavors into plastic-based packaging films is described in Figure 9.3. Using this technology, food grade aromas/flavors can be embedded directly into plastic films during manufacturing so that they form an integral part of the package. This technology is claimed to be applicable to most existing manufacturing methods, including blow molding, injection molding, thermoforming, and extrusion, and in gaskets and liners. CompelAroma® technology can be used in containers, trays, cups, closures, bottles, and flexible packages. The first commercial application of CompelAroma® technology was in Aquaescents® refillable water bottles marketed by NutriSystem™ (USA). Microencapsulated flavors and aromas have also been adapted for microwave and frozen foods packaging containers. Yeo et al. (2005) encapsulated flavor oil in complex coacervates using gelatin and gum Arabic. The resultant microcapsules were incorporated into packaging films used for frozen or baked foods such as breads, pastries, pizzas, and cookies to improve their appeal and release the flavor oil of interest during heating.

Microencapsulated Pigments Coloring agents containing natural or synthetic substances are commonly used as additives in the manufacture of food products. Commercially available coloring agents can contain synthetic substances including dyes or azodyes or natural pigments. It is a well-known problem in the food industry that coloring agents tend to migrate within the food product or into the environment of the product. This problem is particularly troublesome if it occurs in food products that comprise multiple, separated compartments or layers where the coloring agent is not added to all of such compartments. One typical class of such a compartmentalized or layered food product is cakes and other desserts, which comprises at least one layer

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of fruit filling, e.g., in the form of jelly, to which a coloring agent is added, and one or more layers of other ingredients also having an aqueous phase to which the coloring agent is not added. It is evident that migration of coloring agent into the non-colored layers results in a highly unacceptable appearance of these layered products. Another important product in which the migration of coloring agent is not desirable is surimi. Surimi is a stabilized, myofibrillar protein system prepared from fish mince that has been washed with water and blended with cryoprotectants (Park and Morrissey, 2000). Surimi color is a very important attribute to the product’s overall quality since it is commercially graded based on its color. Surimi loses its color even if it is stored at freezing temperature. Floros et al. (1997) discussed the use of coloring agent–containing film in surimi systems as an alternative to traditional direct color addition and to avoid migration of coloring agent from the film to the product. Shahidi and Pegg (1995) described a process in which the coloring agent was encapsulated within a mixture of carbohydrate-based wall material, a binding agent, and a reducing or sequestering agent to improve color stability of surimi as well as other meat products. The encapsulated pigment was reported to be effective by imparting the typical cured color to frankfurters even after 18 months of storage. Popplewell and Porzio (2001) encapsulated various coloring agents in partially hydrogenated vegetable oil as a means of incorporating them into edible coating for snacks, chicken legs, fish, and similar products. In human nutrition, astaxanthin (reddish-orange pigment) has been gaining widespread popularity as a dietary supplement due to its powerful antioxidant properties. As most carotenoids, astaxanthin is a highly unsaturated molecule and thus can easily be degraded by thermal or oxidative processes during the manufacture and storage of foods. This degradation can cause the loss of their nutritive and biological value as well as production of undesirable flavor or aroma compounds. Due to their intrinsic high instability, these compounds are not usually handled in their crystalline form, but rather as stabilized emulsions or microcapsules. Higuera-Ciapara et al. (2002) microencapsulated synthetic astaxanthin in a chitosan matrix cross-linked with glutaraldehyde using the method of multiple emulsion/solvent evaporation. A powdered product was obtained containing microcapsules with a diameter of 5–50 µ. Stability of the pigment in the microcapsules was studied under storage at 25°C, 35°C, and 45°C for 8 weeks by measuring isomerization and loss of concentration of the pigment. Results showed that the microencapsulated pigment did not undergo isomerization or other chemical degradation under the investigated storage conditions.

Microencapsulated-Inks and Time–Temperature Indicators Sakojiri and Takahashi (1990) developed a multicolor imaging material that comprised a substrate and a photosensitive layer. The latter consisted of a heat-meltable microcapsule layer and a color forming layer comprising a diazonium compound and a basic substance. The imaging material can be coated onto paper and polymeric films, and the final product can be used as a food packaging material. Tajiri et al. (1992) formulated microcapsules containing ink for flexographic applications in which encapsulation of the ink ensures its adhesion and flowability. Resins used for this application consist of methacrylate or acrylate of molecular weight of 3000 up to 50,000 g/mol. The microcapsule containing ink compositions for flexographic printing were described to be particularly useful for perfume ink compositions. Chul et al. (2005) prepared an encapsulated color electronic ink by in situ polymerization utilizing urea/melanine and formaldehyde resin as wall materials. The electrophoretic



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medium was made of two different types of white and colored pigment particles, bearing charges of opposite polarity, in a colorless dielectric fluid. Optical contrast was achieved by moving charged particles separately to the opposite electrode. White or colored particles held electrostatically to the common electrode depending on the electric field and the particle charge. The white particles modified with polymethylmethacrylate copolymer and the colored ones (magenta, yellow, and cyan) modified with wax material were found to have superior affinity for the suspending medium. More sophisticated applications of microencapsulated inks and coloring agents can be found in the area of time–temperature indicator applications. Because temperature abuse is common during storage, transportation, and handling, these indicators are designed to monitor temperature abuses in the shelf-life of food products. Temperature abuse does not only cause quality and nutritional losses, but also may lead to food poisoning and food losses (Ozdemir and Floros, 2004). In these systems, polymers that contain irreversible thermochromic dyes change color in response to exposure to predetermined temperature over time. These indicators can be formed into labels that can irreversibly change color and warn the consumer when a product has been exposed to a temperature/time abuse. Successful time–temperature indicators must satisfy basic requirements to be effective as monitoring devices (Selman, 1995): 1. 2. 3. 4.

They must be easily activated and sensitive. They must provide high degree of accuracy and precision. They should have tamper-proof and should not be removed from the package. Response should be irreversible, reproducible, and should correlate with food quality changes. 5. Response should be easily readable and not be confusing. 6. Physical and chemical characteristics of time–temperature indicators should be determined. Recently, Avery Dennison Corp. (US) introduced a new time–temperature indicator in which TT Sensor™ is employed. The TT Sensor™ consists of two labels: an indicator label and a transparent activator label. The activator label is applied to the indicator label and then immediately dispensed onto the package. Once the time–temperature indicator is activated, the indicator label immediately and irreversibly changes color. Activated labels function in the temperature range from –18°C to 60°C. These indicators are claimed to be simple, reliable, and cost-effective for monitoring time–temperature abuse that fresh foods are normally exposed to. In addition, TT Sensor™ labels do not need to be refrigerated prior to application. Another time–temperature indicator that uses microencapsulation technology is called Thermax™. By measuring the change in temperature that is reflected in irreversible color changes, the latter indicator shows whether a food product was exposed to extreme temperatures, and this indicator is tamperproof. Similarly, Prusik et al. (2000) patented a time–temperature indicator label to measure the length of time to which a food product is exposed under temperature abuse conditions. The label contained a microencapsulated heatfusible substance, which can melt and flow when a food product is exposed to temperatures above a predetermined level. The indicator can be activated by light finger pressure or preferably by appropriate automated mechanical means to rupture the capsule containing the heat-fusible substance. A distinct color would develop upon contact of the dye precursor and dye activator due to the migration of the heat-fusible substance.

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Future Perspective Microencapsulation has a promising future in food packaging. Attempts at microencapsulating flavors, antimicrobials, fragrances, coloring materials, and printing inks into food packaging materials will continue to increase in the next decade. There are significant opportunities in microencapsulation for food packaging, such as self adjusting sell-by-date that senses when the consumer opens a packaged food and flashes if the food in the package is spoiled or poses a health risk for the consumer. Another potential commercial application of microencapsulation in food packaging is package indicators that inform consumers if the package is disposable or not. This is especially useful for the elderly and children. The next step in encapsulation is the development of smart microcapsules that embody multiple micro-compartments, each one dynamically interacting with the other, depending on the changing environmental conditions. This is especially important to form packages that have “self-pasteurizing” or “self-sterilizing” capabilities. In these systems, microencapsulated active agents within a polymer matrix will be released in a controlled manner depending on the characteristics of the food such as microbial load, pH, and water as well as the changing environmental conditions such as temperature, relative humidity, and so on to achieve a homogeneous pasteurization or sterilization within the package.

References Ashcraft, C. R. and Wong, M. M. L. 1993. Flavor burst structure and method of making the same. US Patent No. 5,249,676. USA. Barabolak, R. M., Zibell, S. E., Witkewitz, D. L., and Greenberg, M. J. 2005. Method of controlling release of antimicrobial agents in chewing gum. US Patent No. 6,955,827. USA. Barnes, A. C. and Cummings, S. G. 1987a. Cellular encapsulation of biological pesticides. US Patent No. 4,695,462. USA. Barnes, A. C. and Cummings, S. G. 1987b. Cellular encapsulation of pesticides produced by expression of heterologous genes. US Patent No. 4,695,455. USA. Barnes, A. C. and Edwards, D. L. 1989. Cellular encapsulation of biologicals for animal and human use. US Patent No. 4,861,595. USA. Bok, S. H., Lee, H. W., Son, K. H., Kim, S. U., Lee, J. W., Kim, D.Y., and Kwon, Y. K. 1993. Process for preparing coated microbial pesticides and pesticides produced therefrom. US Patent No. 5,273,749, USA. Brar, S. K., Verma, M., Tyagi, R. D., and Valero, J. R. 2006. Recent advances in downstream processing and formulations of Bacillus thuringiensis based biopesticides. Process Biochemistry, 41(2): 323–342. Brody, A. L. 1992. Flavor, flavor everywhere-but in packaging? Cereal Foods World, 37(11): 834–835. Cannon, R. J. C. 1993. Prospects and progress for Bacillus thuringiensis based pesticides. Pesticide Science, 37: 331–335. Chacon, P. A., Buffo, R. A., and Holley, R. A. 2006. Inhibitory effects of microencapsulated allyl isothiocyanate (AIT) against Escherichia coli O157:H7 in refrigerated, nitrogen packed, finely chopped beef. International Journal of Food Microbiology, 107(3): 231–237. Chul, A. K., Meyoung, J. J., Seong, D. A., Gi, H. K., Seung-Youl, K., In-Kyu, Y., Jiyoung, O., Hey, J. M., Kyu, H. B., and Kyung, S. S. 2005. Microcapsules as an electronic ink to fabricate color electrophoretic displays. Synthetic Metals, 151(3): 181–185. El-Rehim, H. A. A., Hegazy, E. A., and El-Mohdy, H. L. A. 2005. Properties of polyacrylamide-based hydrogels prepared by electron beam irradiation for possible use as bioactive controlled delivery matrices. Journal of Applied Polymer Science, 98(3): 1262–1270. Floros, J. D., Dock, L. L., and Han, J. H. 1997. Active packaging technologies and applications. Food, Cosmetics and Drug Packaging, 20: 10–17. Fraser, A. D. 1988. Package opening system. US Patent No. 4,720,423. USA. Higuera-Ciapara, I., Felix-Valenzuela, L., Goycoolea, F. M., and Argüelles-Monal, W. 2002. Microencapsulation of astaxanthin in a chitosan matrix. Carbohydrate Polymers, 56(1): 41–45.



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Jones, L. R. and Hill, J. L. 1982. Composition for pest repellent receptacle. US Patent No. 4,320,112. USA. Klein, R. B., Selph, J. L., Partridge, J. J., and Reinhard, J. 2004. Compounds and methods for controlling fungi, bacteria and insects. US Patent Application No. 20,040,235,898. USA. Lechelt-Kunze, C., Simon, J., Zitzmann, W., Kalbe, J., Muller, H. P., and Koch, R. 2000. Biological material embedded in hydrogels, a process for the embedding thereof, and its use as artificial seed. US Patent No. 6,164,012. USA. Lee, S. J. and Rosenberg, M. 2000. Whey protein-based microcapsules prepared by double emulsification and heat gelation. Lebensmittel-Wissenschaft und Technologie, 33: 80–88. Marrone, P. G. 1999. Microbial pesticides and natural products as alternatives. Outlook on Agriculture, 28(3): 149–154. Navarro, S., Finkelman, S., Zehavi, D., Dias, R., Angel, S., Mansur, F., and Rindner, M. 2005. Pest-impervious packaging material and pest-control composition. US Patent Application No. 20,050,208,157. USA. Ozdemir, M. 1999. Antimicrobial Releasing Edible Whey Protein Films and Coatings. Ph.D. Dissertation. Purdue University, West Lafayette, IN. Ozdemir, M. and Floros, J. D. 2001. Analysis and modeling of potassium sorbate diffusion through edible whey protein films. Journal of Food Engineering, 47(2): 149–155. Ozdemir, M. and Floros, J. D. 2003. Film composition effects on diffusion of potassium sorbate through whey protein films. Journal of Food Science, 68: 511–516. Ozdemir, M. and Floros, J. D. 2004. Active food packaging technologies. Critical Reviews in Food Science and Nutrition, 44(3): 185–193. Popplewell, L. M. and Porzio, M. A. 2001. Fat-coated encapsulation compositions and method for preparing the same. US Patent No. 6,245,366. USA. Prusik, T., Arnold, R. M., and Fields, S. C. 2000. Time-temperature indicator device and method of manufacture. US Patent No. 6,042,264. USA. Radwan, M. N. and Allin, G. P. 1997. Controlled-release insect repellent device. US Patent No. 5,688,509. USA. Rieth, J. P., Wilson, W. T., and Levin, M. D., 1986. Repelling honeybees from insecticide-treated flowers with 2-heptanone. Journal of Apicultural Research, 25(2): 78–84. Rosenberg, M. 1997. Milk derived whey protein-based microencapsulating agents and a method of use. US Patent No. 5,601,760. USA. Sakojiri, H. and Takahashi, H. 1990. Multicolor imaging material. US Patent No. 4,916,042. USA. Selman, J. D. 1995. Time-temperature indicators. In: Active Food Packaging. pp. 215–237. M. L. Rooney (Ed.). Blackie Academic and Professional, London. Shahidi, F. and Pegg, R. B. 1995. Stabilized cooked cured-meat pigment. US Patent No. 5,425,956. USA. Spector, D. 1981. Self-stick aroma-dispensing tab. US Patent No. 4,277,024. USA. Sprinkel, Jr. F. M. and Newsome, R. W. 1988. Package with means for releasing aromatic substance on opening. US Patent No. 4,717,017. USA. Sun, R., Quintus-Bosz, H., Given, P., Pineiro, R., and Morrison, A. 2000. Aroma release bottle and cap. US Patent No. 6,102,224. USA. Tajiri, M., Wakata, K., Shinmitsu, K., and Shioi, S. 1992. Microcapsule-containing ink composition for flexographic printing. US Patent No. 5,120,360. USA. Thomas, T. R., Belias, W. P., Chen, P. N., and Kolovich, N. A. 2005a. Packages with active agents. US Patent Application No. 20,050,220,375. USA. Thomas, T. R., Long, S. P., Belias, W. P., and Kolovich, N. A. 2005b. Packages with active agents. US Patent Application No. 20,050,220,374. USA. Toreki, W., Manukian, A., and Strohschein, R. 2004. Hydrocapsules and method of preparation thereof. US Patent No. 6,780,507. USA. Waters, J. R., Sharp, J. C., and Dev, V. J. 1994. Infection caused by Escherichia coli O157:H7 in Alberta, Canada, and in Scotland: A five-year review, 1987–1991. Clinical Infectious Diseases, 19: 834–843. Wheeler, D. A. 2001. Surface coatings. US Patent No. 6,312,760. USA. Yeo, Y., Bellas, E., Firestone, W., Langer, R., and Kohane, D. S. 2005. Complex coacervates for thermally sensitive controlled release of flavor compounds. Journal of Agricultural and Food Chemistry, 53(19): 7518–7525. Young, S. L., Sarada, X., and Rosenberg, M. 1993a. Microencapsulating properties of whey proteins. 1. Microencapsulation of anhydrous milk fat. Journal of Dairy Science, 76: 2868–2877. Young, S. L., Sarada, X., and Rosenberg, M. 1993b. Microencapsulating properties of whey proteins. 2. Combination of whey proteins with carbohydrates. Journal of Dairy Science, 76: 2878–2885.

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10 Marketing Perspective of Encapsulation Technologies in Food Applications Kathy Brownlie

Introduction From being the enabling technology behind carbonless paper and “scratch and sniff ” fragrance sampling, microencapsulation technologies have found a broad range of industrial applications in markets as diverse as pesticides and cosmetics. Microencapsulation has also found widespread use in the food and beverage industry. Flavorings that last longer, both in the mouth and on the shelf, fresher tasting flavorings which are clearly distinguishable from each other, innovative new flavor combinations, flavors which are released at the ideal time to provide maximum impact for the consumer, and even products which initially taste of one thing, but then develop a totally different flavor as you chew, all of these things are being achieved in food products through the innovative use of microencapsulation techniques. Flavor microencapsulation, for example, entraps tiny volumes of the flavoring substance in a protective layer of another material, creating particles which are only in the micron or even nano size range, but which can have a huge impact on the flavor profile of the final product they are used in. This ability to isolate tiny amounts of a substance within a protective wall or matrix has played a crucial role in the development of novel groundbreaking products, such as the temperature-regulating clothing sold by Outlast and Frisby Technologies and the electronic displays being developed by E Ink. The combination of a constant flow of innovative new techniques with wider application areas and an increased desire for product differentiation will continue to drive growth in the use of microencapsulation technologies in various markets. But, technology providers must choose their end application market with care to ensure sustained growth. Growth rates in the end-use markets range from negative figures to as much as 30 percent. Several potentially high-volume applications of the technology are still in development, and the companies involved have strong intellectual property positions. In other markets, the end-product manufacturers perform most of the microencapsulation themselves and allow fewer opportunities for companies outside the industry. However, in areas such as the cosmetics and in some food ingredient markets, most of the microencapsulation is performed by smaller technology providers. From a performance standpoint, encapsulation of active pharmaceutical ingredients enables the formulator to design a release profile most appropriate for the drug. This includes fast-dissolve formulas, extended release, targeted release, and delayed release. Microencapsulation technologies also enable taste masking of bitter compounds in chewable tablets, as well as oral dosages that are taken without water. In the pharmaceutical consumer product industries, oral drug delivery continues to dominate the microencapsulated drug market. Although some of the microencapsulation

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technologies have existed for decades, the current trend is to explore drug delivery for increasingly potent or insoluble new compounds or to add value to existing compounds.

Key Challenges Identification of New Applications Although the number of markets in which microencapsulation technology has been applied is already large, the general feeling is that the surface of possible applications has only been scratched. Companies offering this technology have to continue to invest in research and monitor markets and emerging technologies where microencapsulation could add value to products or solve particular problems. For companies possessing in-house microencapsulation capabilities, internal communication between research departments is crucial in order to fully utilize these resources. For companies offering microencapsulation services, this can be a much harder task. It is important for such companies to develop a widely recognized reputation as experts in this field, so that industry turns to them when projects which might benefit from this expertise arise. Developing close relationships with R&D departments at various companies will be vital.

Raising Awareness of Technique Potential Closely related to the identification of new applications for the technology is the education of as wide a customer base as possible of the potential of microencapsulation technologies. The primary approach for achieving this within the industry appears to be simply talking to people about the possibilities and gaining a reputation as an effective and innovative provider of such technology. This can be a laborious and slow process, so companies may need to be creative in the ways in which they market their capabilities in this field.

Extra Costs Associated with the Use of Microencapsulation The design of a microencapsulation process for a substance, the equipment needed to apply it on an industrial scale, and subsequent production all add to the cost of products using microencapsulated products. These issues tend to limit the use of microencapsulation technology to few markets: (i) those with higher value products where the cost added by microencapsulation would have less impact, (ii) to those markets where microencapsulation is absolutely necessary, or (iii) to a few markets where economies of scale can be applied, thus reducing the importance of the fixed costs associated with microencapsulation. In other markets, microencapsulation must be seen to provide a very clear added value to the customer, so that they will be willing to pay a higher price. Although this might be clear to the company doing the encapsulation, it is often not easy to sell this to clients and may take a lot of persuasion and increased sales costs in the process.

High Pace of Technical Innovation Although many microencapsulation techniques have been around for a number of years now, it is still a very active research area, in which there is a constant stream of new, improved techniques and consequently patent applications. In order for companies to offer the latest, and best, solutions to industry problems using microencapsulation, and to be able


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to react to new market opportunities, they need to keep track of new technical innovations and to develop their own techniques as quickly as possible.

Client Communication Whether the client be another company or simply another department in the same company, effective communication during a project to make use of microencapsulation technologies is vital to the project’s success. This can often be no easy matter due to the complex scientific nature of many such projects. In addition, a high level of trust needs to be built between the parties concerned, with what may be quite sensitive projects due to the high degree of innovation and possible high returns. Realistic project goals need to be set, including highlighting technical limitations. A thorough initial screening of the technical possibilities is also vital. Care needs to be paid to communication between technical and marketing departments, so that the resulting products are deemed marketable as well as technically innovative.

Scale-up of Processes to Manufacture High-Volume Products The scale-up of any chemical process to an industrial level always presents new challenges. The physical properties of bulk reactions differ markedly from those present in a laboratory scale reaction, adding a level of complexity, which needs to be taken into account during the design of the process. These scale-up challenges can be significant even for the simplest chemical processes; for microencapsulation, it is even more challenging due to the fact that most laboratory scale reactions are not completely understood. The commonly used statement that microencapsulation is as much an art as a science bears witness to the problems that are faced in scale-up, the major problem being the reproducibility of reactions to produce a consistently good-quality encapsulation of the substance.

Technique Differentiation Although most microencapsulation techniques can be related to a relatively small number of basic principles, variations on these have resulted in a quite bewildering array of different techniques being available on the market. Whichever industry a company is targeting, a company with a particular proprietary technique faces the hard challenge of selling the advantages of its own technique over others on the market. The best way to do this is to identify the key defining characteristics of the technology, breaking this down to a few easily recognizable advantages, and putting these to potential clients in a strong and clear message. Of course, different strategies will need to be employed for the different industries to which the technique might be applicable. Certain factors may be particularly of interest in one market, and these should be identified and highlighted. The further sections of this chapter should provide a clear indication of what these might be in the markets covered.

Identification of High-Volume End Uses Many microencapsulation applications are conducted on relatively small scales of perhaps a few tonnes or less. Whilst these may be of a high value, the high cost of development ultimately reduces the profits available from such applications. It has been mentioned time

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and again to Frost and Sullivan during the course of the research that many companies are looking for the next high-volume industrial use of microencapsulation technology, which might rival the volumes used in the carbonless paper industry. The most likely candidates for this would appear to be microencapsulated phase change materials or possibly electronic ink applications if both of these markets expand to their full potential.

Identification of Technology Potential by Market Participants Many companies have developed microencapsulation techniques or brought in technology for their own in-house applications. Often, this has been as far as those companies have taken the process. Without continued R&D in the area, they may find that the technique they are applying is no longer the most suitable or has become uncompetitive compared to microencapsulated products produced by other companies. As microencapsulation in many ways is still very high tech, quite expensive, and often requires a lot of experience to perform, the ability to achieve is still of high value and may be more marketable than some companies realize. It may be that they do not want to go to the trouble or expense of outsourcing the technology. Such companies may also represent a business opportunity for specialist microencapsulators who might be able to demonstrate the cost benefits of a more modern technology, which could be licensed out.

Overview—Microencapsulated Food Ingredients Microencapsulation of food ingredients is not a new concept. Earlier efforts to encapsulate flavors were based on spray drying using acacia gum as the coating materials. However, the ever-increasing complexity of food products is continuing to drive research into novel and different encapsulation techniques and processes. In particular, the rapid growth in functional food seen toward the end of the 1990s is continuing apace, and it is the unstable or unpalatable nature of many of the active ingredients used in these products, which will continue to open up new opportunities for the use of microencapsulation technologies in the food industry. Microencapsulation of food ingredients is performed for a wide number of reasons, including improved substance stability, taste masking, ease of handling, and controlled release. Today, a wide range of food ingredients are microencapsulated using one technique or another. Table 10.1 lists examples of microencapsulated taste-masking solutions currently on the market. This chapter by no means provides an exhaustive reference to all the areas in the food industry to which microencapsulation is being applied, but will attempt to provide a flavor of a few of the most interesting areas, where high-value microencapsulation technologies are being applied to bring improvements to the food products we eat.

Reasons for Encapsulation As has been discussed by other authors in this book, the main reasons for the microencapsulation of food ingredients can be outlined as follows: 1. Protection—This is surely the primary reason for the microencapsulation of food and feed ingredients. Protection can be achieved from a wide variety of influences that might cause an ingredient to lose its functionality; this might be simply physical



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Table 10.1. Microencapsulated food ingredient market: Examples of companies offering microencapsulation taste-masking solutions on the market (source: Frost and Sullivan) Company

Product/brand

Specific application

Bio Dar Encapsulates

Chewing gum applications

Coating Place Colorcon

Protected by masking bitterness of herbal flavors Barrier coatings Opadry®

BASF

Kollicoat® SR 30D

Fuiz Technology

Cerform and Shearform

Particle Dynamics

Micromask

Tailor-made masking Taste masking, pharmaceuticals and foods Mainly pharmaceuticals with food capabilities Taste masking using spun sugars for food and pharmaceutical applications Pharmaceutical and foods

processes such as heat, light, or moisture, which might degrade the ingredient before it has time to act. It may also involve retarding interactions between substances in a given food formula, thus ensuring product’s acceptable shelf-life. 2. Controlled release—Microencapsulation can be used in a delivery capacity whereby an ingredient is released at the required time and place. This could mean the release of a leavening agent at a certain temperature during baking, a flavor upon chewing, or a probiotic culture upon digestion in the small intestine. 3. Processability—Microencapsulation techniques can simply be used to allow easier handling of an ingredient during production of the product. The advantages of providing a dry powdered form of a flavor to a bakery that otherwise only uses powdered ingredients are obvious. 4. Taste masking—Vitamins and minerals are increasingly being added to food to increase actual or the consumer’s perceived health benefits of the product by the consumer. Many of these ingredients are unpalatable, and their taste needs to be masked until they have passed the taste buds and the mouth area. This reason for encapsulation is particularly prevalent in the animal feed industry, where larger concentrations of such ingredients are added in order to produce healthier and hence better yielding animals.

Modes of Release If you have encapsulated an ingredient, you will want it to be released from that encapsulant in order for it to function within the food product at the desired time and place. The most common modes of release are detailed below: 1. Thermal release—Whereby the encapsulant melts at a certain temperature, usually during cooking of the product, releasing the ingredient. By altering the type of coating and its thickness, it is possible to ensure release of an ingredient within a few degrees of the required temperature. 2. Physical release—Requiring the physical breaking of the microcapsules; usually this mode of release is designed for ingredients that need to be released during chewing. Factors which can be altered to prolong or otherwise the release profile include the size of the capsules and the strength and flexibility of the coating.

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3. Dissolution—Most food products contain at least a small amount of water, which can be used to ensure the release of an ingredient enclosed in a water-soluble coating. The chemistry of the coating can be designed so that this only occurs at a particular pH, temperature, or salt concentration.

Market Drivers Examples of key market drivers for microencapsulated food ingredients include:

Increased Consumption of Processed Foods which Require Ingredient Stabilization Sales of processed and pre-prepared foods, commonly known as de-cooking phenomenon, continue to increase. This essentially means that people are devoting less and less time to the preparation of their food, and so are using less fresh ingredients and more that are prepared in some way to speed cooking. The increased processing that these products may undergo, including pre-cooking and freeze–thaw cycles, can harm many ingredients in the food products, resulting in lower quality for the consumer. Microencapsulation can protect many of these ingredients during processing and then be designed so as to release them when needed, either during the final cooking process or upon consumption.

Rapid Growth in the Functional Food Market Sales of functional foods have increased dramatically since the mid 1990s. This category is best represented by probiotic milk drinks or vitamin fortified sports bars and cereals. Obviously, such products need to contain some ingredients which will impart this benefit, and many such ingredients are unstable or difficult to handle such as vitamins, minerals, amino acids and herbal extracts.

Drive for Brand Differentiation Increases Call for Microencapsulated Ingredients Food manufacturers are responding to more complex consumer requirements and increasing competition, particularly from the powerful supermarket’s own innovative brand products and product lines. The use of ingredients or processes which impart some novel characteristic to a food product, such as a new taste or health benefit, is a key tool in selling more expensive branded products to consumers. Many such innovations are always copied in some way by the supermarkets, creating a cycle of innovation, which can only increase the use of such high-tech processes within the food industry.

Consumer Demand for Natural Food Products The continuous string of public health scares surrounding the food industry, as well as greater awareness among consumers of the benefits of a healthy diet, are driving the demand for food products which are natural in origin. Many of these natural ingredients are however unstable to harsh environment of food processing and cooking, so in order to



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ensure the survival of such ingredients through consumption, microencapsulation is being used to protect them.

Microencapsulation Reduces Amount of Ingredient Required for Same Effect Whilst many microencapsulation techniques are often considered too expensive for application to food ingredients, on some occasions, the use of such technology can actually result in a cost saving. The protection of food ingredients until they are required can result in the need for much less of that ingredient in the product, possibly producing significant savings on raw materials.

Complexity of Technical Requirements Creates Opportunities for Specialist Companies The complexities of encapsulation processes often mean that an entirely new procedure needs to be developed for a given application or a new ingredient. Different problems may also call for the use of totally different technologies. Food ingredient manufacturers cannot possibly have all the equipment and technical know-how in-house in order to cater for each possible new problem or innovation. This creates an increasing demand for contract microencapsulation services. Small contract companies have the flexibility to respond to customer needs. They will often produce very small volumes, which would not be economically feasible for a larger company to do.

Tightening of Laws on Product Claims may Force Companies to Use Microencapsulation The increasing focus on quality of food products, driven by consumer demand for more information about the food they consume, will undoubtedly lead to tighter regulations governing the product claims that food manufacturers make. At present, in many countries, it is simply necessary for companies to introduce an ingredient at the outset of the production process, without ensuring that the stated level is actually present in the finished product. Often, sensitive ingredients such as some vitamins are destroyed by the cooking process, making claims for the extra health benefits of such added substances essentially false. If producers have to ensure that the ingredients survive until consumption, the protection of these ingredients would become vital, leading to new opportunities for developing and using novel microencapsulation technologies.

New Product Development Creates Future Markets The development of an encapsulation process for a new ingredient or new purpose is often an expensive and time-consuming procedure, which will not be undertaken unless a decent return on that investment is expected. One of the best ways for companies providing microencapsulated food ingredients to identify where to focus their research is by undertaking contract work. Each new request, whether it results in an order or not, brings a new idea or indication of a market need, which can hopefully be exploited.

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Market Restraints Examples of the key market restraints for microencapsulated food ingredients include:

Cost of Many Microencapsulation Techniques Reduces Scope for Use in Food Products The cost of most microencapsulation techniques is a serious constraint to the use of this technology in the food industry, where traditionally the end-user markets have been mature and price sensitive. An alternative scenario is its use in those situations where encapsulation is the most cost-effective solution to a particular problem.

Lack of Industry Awareness of Microencapsulation It is still felt that many food processors are not aware of the possible advantages which microencapsulated ingredients can bring to their products. Combined with this are misconceptions about such things as the cost of these ingredients and concerns over the increased level of processing which they might represent. The desired widespread knowledge of these techniques within the food industry will undoubtedly take a long time to build up and will limit the wider use of the technology in the process.

Difficulties in Technical Communication with Customers Related to the above constraint is a common complaint from many encapsulation specialists that companies approaching them do not understand the nature of microencapsulation. Whilst they generally welcome any approaches for business, this is obviously a source of frustration within the industry, and the wasted time and effort can have financial implications. In addition, if clients go away with a poor impression of microencapsulation due to unrealistic expectations, this will have an impact on the future market potential for such technology. It is the encapsulation companies themselves, as providers of the service, who need to communicate effectively with their potential clients, so that realistic project objectives are agreed upon, which will result in satisfaction for both sides.

Limitations on Encapsulant Materials There are a number of limitations on the materials which can be used to encapsulate actives which may ultimately lead to technical and supply problems: BSE and Foot and Mouth The Bovine spongiform encephalopathy (BSE) epizoolic has created a consumer confidence crisis in the safety of materials derived from animal sources. Products using encapsulation are often functional foods bought by very health conscious consumers, who are aware of such issues. Thus, the presence of gelatin may cause concern among consumers. The recent foot and mouth disease epizoolic in the UK and the resulting ban on the export of animal products also caused an increase in gelatin prices by as much as 20 percent.



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GMO Consumer demand has led to most food manufacturers in Europe, in particular, being very careful not to use ingredients that might come from genetically modified organisms in their products. This has affected supplies of certain materials such as maize-derived starches from the US. Approval of Ingredients The European Union maintains a list of chemicals that have been approved for use in food. This may limit the development of novel processess that may require materials not on the approved list. Competitive Factors One key competitive factor in this market is technology. The ability to consistently deliver added value to food products through the use of a microencapsulation is vital for companies using this technology. It is not an easy process to sell simple products such as these at much higher prices than normal, so customers must be convinced that the microencapsulation is achieving the desired properties in their products. The ability to deliver something different and superior in terms of performance is the key to attracting more customers in this market. Another important competitive factor, as in the provision of microencapsulated products in many other industries, is customer service. With most ingredients being designed for specific applications, often at the request of customers, close attention to delivering on customer service and maintaining good relationships is important to maintain market share. Another key competitive factor is technical expertise, as the microencapsulation has to achieve the desired result in the final product in order for customers to continue to pay higher prices for these products. Properties of the encapsulation are often tuned to the customer’s requirements for a particular application, so close attention to customer service is very important to ensure the product is successful and repeat business is gained. Microencapsulation of flavorings undoubtedly adds some cost to the production, which is generally reflected in higher prices. Respondents were very unwilling to discuss what actual price the microencapsulation added to a flavoring, mainly due to the fact that this can vary greatly according to the technique applied, the volume of product made, and the dose rate of that flavoring. In addition, the added value of the microencapsulation was often felt to result in cost savings for customers due to lower wastage of the volatile flavorings and better impact in the product, resulting in the need to use lower volumes. Microencapsulation techniques can result in price increases of 2 to 10 times the price of a non-encapsulated flavoring. The prices for microencapsulated flavorings are not expected to mirror this decline as the added value they bring often means that companies are not competing on price against similar products.

Pricing The food industry tends to be price sensitive, so the extra cost associated with microencapsulating an ingredient needs to be fully justified in terms of offering a clear improvement in

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performance of that ingredient within the food product. The application of microencapsulation is more easily justified with higher value ingredients such as flavorings, vitamins and minerals, and probiotics. Price is an important competitive factor, for both non-encapsulated and microencapsulated ingredients. Higher prices of microencapsulated ingredients must be shown to be justified by their better performance. There can also be significant price differences between microencapsulated products from different companies, and here also, improved performance must be demonstrated. Microencapsulation is performed by both the original ingredient manufacturers and companies specializing in microencapsulation technologies. For the latter, it is imperative that their technical expertise allows them to offer something unique in terms of performance. Their hardest task lies in convincing clients of this performance benefit in relation to the higher price of the ingredient. If their message is strong enough, they will face fewer market barriers and lower competition. Companies need to work closely with clients to identify the end-use products that microencapsulated ingredients could add benefit to and design suitable products to meet this need.

Industry Structure Microencapsulation is performed by both the original ingredient manufacturers and companies specializing in microencapsulation technologies. Examples of companies amongst the latter group include Balchem, Particle Dynamics, Bio Dar, and TasteTech. Most of the major flavor houses are actively involved in research into the use of microencapsulation technologies, as are other major food ingredient manufacturers. At a very simplistic level, companies can be divided into two groups according to their capabilities of adding value to their businesses. In practice, there is a significant amount of cross-over between these two definitions: 1. The first type includes companies that are usually small- or medium-sized enterprises for which the ability to do microencapsulation lies at the core of their business and provides their main revenue stream. Such companies market their ability to perform microencapsulation in a number of ways. Close cooperation with their customers is vital and can involve licensing a production process, toll manufacturing, co-development work, or sale of a bespoke product line. Such companies may also sell standard microencapsulated products, or products in which microencapsulation is the core enabling technology. 2. The second type of companies are usually larger enterprises for which microencapsulation is simply another manufacturing technique they have at their disposal and that they can use in one or more product lines. Such companies have usually developed or purchased microencapsulation capabilities for a particular in-house application, but have gone on to apply this knowledge in other areas of their business. They do not generally offer their microencapsulation capabilities to other companies. An exception to this trend is companies such as BASF and 3M. These enterprises have been offering their microencapsulation capabilities to other companies in certain markets. Such companies and few others can really be considered providers of a wide range of microencapsulation expertise, which can be applied for virtually any company in any industry. Such companies specifically advertise their ability to apply their techniques to long lists of substances. Examples of these companies are South West Research Institute, Thies Technology, 3M and Ciba.



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Microencapsulators in Specific Industries Examples include Coletica and Lipotec in the cosmetic industry. In reality such companies, though specialized in certain applications, are often looking for new business opportunities for applying their techniques and would gladly try to adapt them to other industries. Crossover capabilities are often seen in the cosmetic and food industries.

Companies for which Microencapsulation Performs a Vital Role in their Main Product Line For carbonless paper manufacturers, microencapsulation is thus an inherent part of their production lines. Although most companies originally licensed the technology from its developers, through using it for a number of years, they were able to have build up a high degree of expertise in the area. Similar examples can be found in the textile industry.

Companies which Apply Microencapsulation to Certain Product Lines Examples of this category are flavor suppliers that offer some of their flavors for certain end uses in microencapsulated form. Such companies usually bring the technology from an outside source, but through running the processes for a number of years, they develop their own expertise and even research capabilities. Table 10.2 gives examples of companies that are involved in the provision of microencapsulation technologies to the food industry. Balchem Encapsulates Balchem Encapsulates is a wholly owned subsidiary of Balchem Corporation, which was founded in 1967 by the merger of several entities, including Dr Leslie Balassa who owned several technology inventions in the field of encapsulation. It operates in two business segments, Encapsulated Products and Specialty Products.

Table 10.2. Examples of companies active in the food ingredients microencapsulation market (source: various) Company

Website

Aveka Balchem Brace Coating Place Micap Particle Coating Technologies Particle Dynamics Ronald T. Dodge Co. Sono-Tek Southwest Research Institute TasteTech, UK Thies Technology 3M

www.aveka.com www.balchem.com www.brace.com www.encaps.com www.micap.com www.pctusa.com www.particledynamics.com www.rtdodge.com www.sono-tek.com www.swri.com www.tastetech.co.uk www.thiestechnology.com www.mmm.com

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Balchem’s Encapsulated Products business utilizes proprietary microencapsulation technologies in an ever-expanding variety of applications, with food and feed ingredients at its core business. Its major product line ranges from ingredients for bakery products (Bakeshure), confectionary (Confecshure) and wellness products (Vitashure), as well as encapsulated flavors (Flavourshure) and meat-processing ingredients (Meatshure). Its animal feed additives have the trade name Reashure. Balchem also offers partnerships and toll manufacturing capabilities to solve particular problems faced by companies, which might be solved using its technologies. Balchems’ acquisition of the encapsulation and agglomeration capabilities of Loders Croklaan in July 2005 underlines the ambition of this company to grow its core business. Brace The Germany-based company, Brace, specializes in laminar flow break microcapsule forming. The firm holds a wide variety of patents worldwide. Examples of their products include microcapsules of gelatin, alginate, and agar, filled with flavors for use in breath freshening, chewing gum, and ready meal applications. Karmat Coating Industries Ltd Karmat is an Israeli company formed in 1993 and jointly owned by Kibbutz Ramot Menashe and Coating Place Inc. Karmat’s microencapsulation techniques are mainly based on fluid-bed technology, which employs an open air system allowing the use of many different coating materials including modified starches, peptides, cellulose derivatives, fatty acids, and peptides. It applies these to the encapsulation of ingredients for the food, cosmetic, pharmaceutical, chemical, and feed industries. Karmat’s main business is in the microencapsulation of vitamins and minerals, which it incorporates into bespoke premixes for its clients in the food industry. Most products it produces are customized specifically for clients. Its premixes for the dairy sector are called Lactomix, those for baking applications, Bakeamix, and those for use in baby food, Babymix. Other product lines include microencapsulated citric acid, ascorbic acid, and ferrous sulfate. Bio Dar Bio Dar was founded in 1984 as an Israeli–American joint venture. In 1998, the company was acquired by Lycored, a subsidiary of Makhteshim-Agan and part of the large Israeli holding group, Koor Industries. Bio Dar’s main products are microencapsulated vitamins and minerals. It also manufactures microencapsulated nutraceuticals such as carnitine, amino acids, and herbal extracts. Over 50 percent of its products are customized to specific customer requirements. Particle Dynamics Particle Dynamics, Inc. (PDI) is an American-based company acquired in 1972 by KV Pharmaceutical company. PDI markets specialty raw materials for the pharmaceutical, nutritional, food, and personal care industries. It divides its business into three main technology lines; Destab, a direct compression technology used to make tablets for pharmaceutical and



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nutritional supplement purposes, Descote®, a line of microencapsulated vitamins, minerals, and herbal extracts, and MicroMask which encompasses a series of technologies for taste masking mainly in over-the-counter medicines. PDI’s proprietary microencapsulation technology is based on the trapping of ingredients in a matrix, in which particles of the ingredient are effectively embedded. The advantage of this technology lies mainly in its physical stability, being able to better withstand processes such as tabletting. The company follows a lower risk business approach of modifying existing compounds and formulations rather than discovering new molecular entities. Particle Dynamics serves the vitamin, food, and herbal supplement industries and is also involved in pan coating. Particle Coating Technologies Particle Coating Technologies, Inc. (PCT) is a research and development company dedicated to microencapsulation technologies. Formerly part of the University of Washington, Department of Chemical Engineering in St. Louis, MO, the company became independent in 1994. PCT pioneered a spinning-disk coating technique and also specializes in the formation of narrow particle-size distribution products, using a proprietary atomizer. PCT claims more than 20 of the world’s largest 100 public companies as customers and has some toll manufacturing capabilities in addition to its core work in feasibility studies. TasteTech TasteTech is a privately owned British company founded in 1992 and currently distributes its ingredients worldwide. It utilizes its proprietary microencapsulation technology to encapsulate flavors, spice extracts, and key ingredients used in the food industry. It also applies its technology in the pharmaceutical and cosmetic industries. TasteTech employs three main microencapsulation technologies as well as spray drying capabilities. Its controlled release techniques are labeled CR100, CR200, and CR300 and are used to encapsulate the ingredients mainly using vegetable fats and oils. The advantage of using these encapsulant materials is the ability to control the release of the ingredients by adjusting the melting point of the fat coating.

Key End-User Groups In terms of the microencapsulation technology itself, almost any company in the chemical, food, and related industries is a potential end user. The number of areas the techniques are being applied to continues to grow as more research is carried out and more projects attempting to harness microencapsulation capabilities are undertaken.

Competitive Factors Table 10.3 gives examples of some of the factors taken into consideration in the selection of a microencapsulation technology. For those companies marketing their ability to perform microencapsulation for other companies in any market, an important competitive factor is reputation. If a company is

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Table 10.3. Microencapsulated food ingredient market: Important factors to consider (source: Frost and Sullivan) Issue

Questions

Importance

Function

Primarily taste-masking is the raison d’etre of microencapsulation What is my budget? Is the technology cost-effective? How small do my encapsulated ingredients need to be? Will the encapsulated ingredient survive processing and storage?

Vital function

Cost Size Production/ conditions Effects

How will the encapsulated ingredient interact with other ingredients in the finished product?

Need to weigh effectiveness, new methods are expensive! Important for mouthfeel, taste, and effectiveness Microencapsulation is ineffective unless it can protect the ingredient from processing and storage Unintentional interactions can ruin a product

recognized as an expert in the field and has previously participated in a large number of successful projects, then approaches from clients are far more likely. Given the unpredictable, project-based nature of much of this business, such industry recognition is vital if a company is to generate a steady stream of work in the area. Other activities which can raise a company’s profile in this way might be to hold as many patents as possible in the area concerned or to regularly publish scientific papers on the subject and give talks at conferences. For any company using microencapsulation, innovative ways of applying the technology are likely ultimately to lead to greater profitability. If the technology can be applied to give a product a competitive edge or to introduce an entirely new concept to the market, high rates of growth in that product may well result.

Examples of Microencapsulation in the Food Ingredient Industry This section reviews the use of microencapsulation technology in the flavors, vitamins, salts and acids, and probiotics markets. In these markets, the use of microencapsulation has moved beyond basic coating for handling purposes toward its use for stability purposes and more importantly, controlled release of the encapsulated substance. The largest market using microencapsulation technologies is that for flavorings. According to Frost and Sullivan (Oxford, UK), microencapsulation of flavors in the European market was valued at $340 million in 2001. Other market sizes and growth rates vary widely, depending on the food ingredients concerned, but overall growth in the use of microencapsulation is undoubtedly being experienced as more food and beverage manufacturers begin to recognize the benefits that some of these technologies can bring. The two major growth areas will continue to be in the functional food sector, where microencapsulation can be used to stabilize ingredients such as vitamins and minerals, and elsewhere in techniques which offer controlled release of ingredients. Both these markets are expected to see double-digit growth in the next few years. The increased processing of foods, coupled with the desire for increased quality and innovation, is driving growth in the use of techniques which can effectively stabilize sensitive ingredients.



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Microencapsulated Flavors Market Flavor is an essential part of our experience when eating food. Four basic flavor types have been identified: sweet, sour, bitter, and salty, with a fifth defined by the Japanese as Umami, a savory flavor. Obviously, many natural foods have their own inherent flavors, but today’s complex food products often require the addition of one or more flavors in order to satisfy the consumer. The major areas of flavoring use are in dairy foods, confectionary, beverages, bakery foods, and other savory foods. Flavors can be derived by physical extraction from natural sources or synthesized. Why Microencapsulate Flavors? Microencapsulation can help protect flavors from the rigors of harsh production processes and in providing a much high sensory impact in the final product. In addition, a more natural flavor can be provided by protecting sensitive extracts and further releasing them at the time of consumption. Finally, flavor manufacturers are simply looking to offer innovative new products to their customers. The protection provided by microencapsulation can be harnessed to allow the use of certain flavors or flavor combinations which were not previously possible in certain products. As discussed earlier, microencapsulating flavors can help in various ways: 1. Protection from degradation. 2. Controlled release at a desired time and rate. 3. Stabilization and shelf-life extension. End-Use Applications The segmentation of market revenues for microencapsulated flavors does not necessarily follow that of the total flavor market due to certain end-use requirements. The major enduse markets for microencapsulated flavorings are listed below: 1. Confectionery products—sustained release of flavorings is often required to add value to the products. The most common type of confectionary that use microencapsulated flavorings is chewing gums. Confectionery is estimated to account for 35 percent of European microencapsulated flavorings market revenues. 2. Bakery products—dry powdered flavorings are required for easier mixing with other powdered ingredients. Controlled release of flavors in baking is also a growing feature of baked goods. 3. Powdered beverages—encapsulated dry powders are necessary for better mixing with other dry ingredients of the beverage components and for enhanced shelf life of the dry mix. Release is achieved through dissolution of the coating. Spray dried flavors are widely used in this market for ease of handling and instant solubility. 4. Processed foods—all the reasons for microencapsulating flavors mentioned above are applicable to its application in processed foods. More advanced microencapsulation techniques are being used in this market sector to address a range of shelf-life and controlled release issues.

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Microencapsulation is a very active area of research at most of the major flavor houses. These companies have large R&D budgets needed to invest in the development of microencapsulation expertise, which can take a lot of practice to perfect. Such a quality-driven market sector also presents opportunities for smaller technology providers. Although profit margins from partnering may be lower than selling your own products, access to the large marketing and sales forces of the industry leaders will maximize the sales potential of the product, which is something that smaller companies can struggle to achieve on limited budgets. Examples of Market Drivers and Restraints in the Flavors Industry Product innovation gives market advantage. Innovative new food products which capture the imagination of the public give food manufacturers a competitive edge in the competitive food market. Such innovation within the food industry is a major driver of the use of microencapsulated flavors, which can add an extra dimension to a food product. Possibilities such as sequential release of flavors, long-lasting flavor effect, or simply the ability to introduce certain flavors into a new food area can all help to increase the appeal of a food product and help it to capture market share. Increasing use of processed foods. Sales of processed and pre-prepared foods continue to increase as the phenomenon known as de-cooking increases. Such systems often require flavors to be protected from the processing they undergo in order that they can be delivered to the consumer when the product is eaten. Consumers demand better food quality. In conjunction with the greater consumption of processed foods, consumers are demanding greater quality from these food products. One particular quality demand is that for more authentic or natural tastes. Microencapsulation can be used to deliver individual, authentic tasting flavors at exactly the right time, resulting in greater customer satisfaction with the product. Examples of market constraints in the flavors industry Drive for lower process costs. Although microencapsulated flavorings cost more than those which are not encapsulated, they can offer cost savings in other ways. Microencapsulation of flavors into dry powders can help in this regard. Less expensive equipment might be needed and production steps removed due to the easy mixing of different powders rather than oil inclusion. In addition, less flavor is likely to be released to the atmosphere during processing, resulting in the need to use less of the product to achieve the same effect. Environmental problems with spray drying lead producers to search for alternative technologies. The use of spray drying, where a fine mist of flavor is heated will inevitably lead to the escape of some of these volatile compounds into the atmosphere, which can require the use of expensive scrubbers to control. Even then, certain flavors such as onion or cheese can be particularly troublesome. Companies using spray drying for flavors are monitored by environmental officials at a national level, who have the ability to impose injunctions stopping the use of the equipment for particular flavorings. This has led producers to look to other microencapsulation techniques for flavor applications. It has been suggested to Frost and Sullivan that if another suitable technique were available to encapsulate flavorings in water dispersible coatings, it would be take a large share of the market from spray dryers.



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Consumer and legislative restraints on encapsulant materials. The European approved ingredient list contains details of those substances which are allowed for use as food ingredients and broadly in which applications they can be used in. Such regulatory constraints present major challenges mainly in limiting the number of materials available, their usage in specific systems, and sometimes at low concentrations that may render them ineffective. Consumer preference can also limit the types of encapsulating material used. A particular example is the movement against genetically modified materials.

Microencapsulated Vitamins Market Vitamins are essential parts of the human diet, without which we are prone to a large number of vitamin deficiency-related diseases and general ill health. Traditionally, we have derived these essential nutrients by consuming a varied diet of natural foods abundant in particular vitamins, such as many fruits and vegetables. The techniques most widely practiced are physical processes such as spray drying, spray cooling, and fluid-bed techniques. Revenues indicated in this document refer to all coated vitamins. Why Microencapsulate Vitamins? The major reasons for microencapsulating vitamins for use in food products are detailed below. In addition to processability and stability issues discussed above for encapsulating flavors, most vitamins have objectionable taste that needs to be masked so that the active can only be released in the gut. The largest volume of vitamins sold in microencapsulated form include the fat- and water-soluble types such as A, D and E, K1, and the B-group (notorious for medicinal taste).

Vitamins in Animal Feed Vitamins are also microencapsulated for use in animal feed products for both taste-masking and bioavailability reasons. The latter is particularly an issue for ruminants, where rumen by-pass products can utilize microencapsulation to ensure that vitamins reach the second gut and intestines in their intact form.

Microencapsulated Salts and Acids Market A variety of other food ingredients have been microencapsulated using mainly fluid-bed techniques; the most common are salts (sodium chloride, sodium bicarbonate, and sodium diacetate) and acids (citric, malic, sorbic, tartaric, ascorbic, acetic, fumaric, etc.). These ingredients are encapsulated for a number of reasons such as controlled release, extended shelf-life, prevention of color degradation, and protection against moisture. Their main end-use applications include confectionery, bakery, and processed meat products.

Microencapsulated Probiotics Market Probiotics are bacteria, yeasts, or other microorganisms which provide health benefits by contributing to intestinal microbial balance. These live cultures of microorganisms are included in a number of food products and supplements and are generally intended to

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colonize the large intestine, where they impart such benefits as impeding harmful bacterial growth, supporting the immune response, increasing the nutrient absorption, and reducing the risk of cancer. Probiotics have been included in a number of food products, which can be broadly classified into two groups—dairy products and other food supplements. Dairy products include yoghurt, sour cream, cottage cheese, ice cream, and fermented milk drinks. Other dietary supplements can be capsules, powders, or tablets. Why Use Microencapsulated Probiotics? One important constraint in the probiotic market is the technical challenges associated with working with live cultures of delicate microorganisms. The bacteria are often sensitive to the conditions found in food products or encountered during processing such as moisture, temperature, oxygen, or pressure. Microencapsulation can protect the bacteria against these conditions as well as control their delivery. It is not expected that microencapsulated probiotics will cannibalize existing probiotic markets, but they will instead open up new markets, either through the inclusion of probiotics in different food products and supplement forms or through the introduction of previously unavailable bacterial strains. The food supplement market will be the first to benefit, with improved probiotic survival rates during tabletting a particularly attractive proposition. Two main challenges can be faced in this application: 1. Higher price, which may be two or three times that for non-encapsulated bacteria. This is undoubtedly the main reason why the microencapsulated products will not affect sales of non-encapsulated ones, where they simply could not compete. However, for those bacteria which cannot be included in food products in any other way, price is not expected to be a major constraint. In fact, increasing survival rates of the bacteria would reduce the need for overdosing, potentially offering savings. 2. Product development time: It is likely that each new bacterial strain to be microencapsulated will need different conditions of encapsulation and will thus pose its own technical challenges. This will undoubtedly slow up the time to market for a wider range of potential microencapsulated probiotic products. Table 10.4 gives examples of companies that have developed microencapsulated probiotic products.

Table 10.4. Microencapsulated food ingredients market: Examples of microencapsulation of probiotic bacteria (source: Frost and Sullivan) Company/group

Product/brand

Specific application

Institut Roselle

Probiocap

Advanced Bionutrition

MicroMatrix®

Rhodia

FloraFit®

University of Maryland

Xanthan-chitosan

Guarantees probiotic stability and survival in cereal bars and yogurt Allows continuous encapsulation of functional foods Designed for supplements and nutritional additives Protects prebiotic coacervation products at 0–60°C



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Examples of Strategic Recommendations for Companies Specializing in Microencapsulation Technologies Indeed, changing consumer trends and tastes are primarily responsible for driving innovation in the microencapsulation market. Since food manufacturers constantly monitor such trends, food ingredient companies are always looking for ways to meet these ever-changing demands, thereby promoting the need for novel microencapsulation technologies. With consumers showing a growing preference for functional food, which now accounts for a substantial chunk of the global nutrition market, food companies are looking for different ways to incorporate health-promoting ingredients that deliver some kind of health benefit to the consumer.

Business Promotion Strategies For companies wishing to promote their microencapsulation capabilities, the promotion of these probably represents the major challenge to the success of the business. Potential clients need be made aware of situations where microencapsulation could add value to a product or solve certain commonly recurring problems. The main method currently employed to get this message across is to personally talk to clients, either through a site visit or at trade shows. Once projects have been undertaken, personal relationships with research departments at clients can hopefully be built, which might result in further business opportunities. To initially catch the attention of potential clients, examples of successful projects producing interesting and groundbreaking results or simply commercially successful products should be emphasized. Technical expertise should be stressed through highlighting academic publications and patents held. Another method of business promotion is to take part in interesting projects, which receive press coverage and indirectly promote both microencapsulation technology and the company involved in the project. One way to spread the cost of this would be setting up an industry association representing all companies involved in the market and who aim at promoting the potential benefits of the technology. There is presently an International Microencapsulation Society, but this is aimed more at academic research than industrial issues. The European Commission has also set up a thematic network entitled “Microencapsulation for Low Cost, High Volume, Pharmaceutical Applications,” intended to provide a guidance manual for European Industry indicating which technique will be most suitable for a particular application. Such a project is exactly what is needed by the industry and could well prove to be the catalyst for significant market growth.

Product Proposal Strategies Maximize Focus on a Single Market Most companies offering microencapsulation technologies start out by applying them to a particular market area, this usually being the one for which the particular technique turns out to be most suitable. Such a focus is important for these smaller entrepreneurial companies initially. Trying to sell the technology to a range of industries would simply dilute the marketing message and prove very difficult for a small company to achieve effectively. Focusing on a single market allows limited funds to be concentrated on a particular

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Chapter 10

customer group, allowing a company to build a reputation in that industry as a reliable technology provider more quickly. Application of Techniques Across Different Markets Whilst the above approach is important initially, the ability to apply microencapsulation techniques to areas other than those where they might first have been used can be very important to the long-term growth. High growth markets using the technology may turn out to be part of a trend, which fade away as quickly as they arrived, so companies need to have other areas to fall back on if this occurs. Particularly susceptible to this are consumer markets, such as the cosmetic area, where trends toward certain ingredients or product types move rapidly. Offer of a Diverse Range of Encapsulation Techniques For companies looking to do business through their ability to do microencapsulation, it is important to be able to offer a broad range of possible solutions to a particular encapsulation problem. This will give such companies the ability to serve as many clients as possible. Companies such as South West Research Institute and Thies Technology in the US have expertise in many different encapsulation techniques, making the chances of a company finding a satisfactory solution more likely. Even for companies focusing mainly on one market, a greater number of product lines again increase the chances of a successful match with a client’s product and should result in more repeat business.

Examples of Strategic Recommendations for Larger Companies Using Microencapsulation Technologies In-House Cross-Fertilization of Technology within the Organization The number of industries, products, and substances to which microencapsulation can be applied is virtually limitless. The broad applicability of encapsulation technologies should be pursued by larger companies, making sure that research scientists in all business segments are aware of the techniques and what they might be able to achieve. Companies which have clearly benefited from such an approach are 3M and BASF. 3M has long been recognized as the leading large industrial user of microencapsulation technologies. Although originally translated to such applications as scratch and sniff fragrance sampling, these technologies are now an inherent expertise within 3M and have been applied to deliver greater product performance and to develop innovative new product lines in a variety of industries including pheremones, oil extraction chemistry, and adhesives. BASF first developed microencapsulation expertise for use in the carbonless paper market, in which it still licenses the technology to a number of major paper manufacturers. It has applied various microencapsulation techniques in most of the industries covered by this chapter including its pesticide formulations, cosmetic ingredients, and food ingredients. Its integrated structure has allowed this cross-fertilization of the technology, which is now being used in unexpected applications such as building insulation via phase change encapsulation technology.



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Offer of Technical Expertise to Other Organizations As has been said time and again about microencapsulation, it is considered as much of an art as a science, so there is no substitute for experience in using the techniques reliably to be able to consistently provide high-quality products. Such experience, especially in the application of techniques to industrial scale production, is a valuable asset and one which companies may be able to directly derive revenues from. A microencapsulation service business could be set up by combining the experience a company has in applying a number of techniques in a range of different sectors and offering them to industry at large. Despite the successful approach of 3M in lending its technologies to other industries such as agrochemicals, cosmetics, food and pharmaceuticals, it did however spin-off some of the business resulting partly in the formation of the company Aveka in 1994, which provides microencapsulation and particle processing to industrial clients. Another large company which has formed a microencapsulation business is Ciba. Ciba offers its expertise in a range of different microencapsulation technologies to other companies and is looking to apply its expertise in particular to high-volume industrial uses.

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Index

Active transport, 179 Actives in food matrices, entrapment of amorphous matrix, 3–5 complexation into cyclodextrins, 5–7 cross-linked or coacervated polymers, 8 emulsions and micellar systems, 7 fat- or wax-based matrices, 7 hydrogel matrices, 8–9 microporous matrices, 7 Alginates, 89 polycation-coated, 90 prebiotics-coated, 90–91 Allyl isothiocyanate, 210–211 Antimicrobial agents, 129–130 Aspartame, 184 Balchem Encapsulates, 231–232 Beeswax, 119 Bifidobacteria, 92 Bio Dar, 232 Bioadhesive devices, 192–194 Bioerodible devices, 192–194 Brace, 232 Candelilla wax, 120 Carbohydrates encapsulation in amorphous matrices, 3 as wall-forming material, 2 Carnauba wax, 119 Cellulose acetate phthalate, 91–92 Chemical leaveners, 127–129 Chewable tablets, 196 Chewing gums, 181 as delivery systems for oral health, 188–189 composition, 182–183

for delivering acetylsalicylic acid, 189 for delivering antimicrobial agents, 187–188 for delivering caffeine, 185–187 for delivering flavors and nonmedicated actives, 183–185 for delivering vitamins, 187 manufacture, 183 vs. lozenge delivery profile, 189–190 Chitosan, 92 Coacervate phase, 150–151 Coacervation, 8 Co-crystallization, 5 Coenzyme Q10, 31–34 Complex coacervation, 150–151 cross-linking of gelatin-based coacervate capsule shells, 160–162 encapsulation process, 157–160 encapsulation technology issues, 162–165 properties, 151–157 solvent exchange, 165–167 Confectionery products as delivery systems, 181 Controlled release systems, complex coacervate-based, 136–139 Controlled release, 1 Core materials, 2 Cosolubilization effect, 18 Covalent bridging, 45 Cross-linked or coacervated polymers, encapsulation in, 8 Cyclodextrins, 5 guest molecules and, 6 molecules, 6–7 type and degree of complexation, 6

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Index

Dairy products (probiotic survival) cheese, 93–94 frozen dairy desserts, 94 yogurt, 94 Dietary fats delivery as o/w emulsion, 65–69 Dilution lines, 17 Dissolution, 225 Double emulsions, 55 general applications of w/o/w emulsions, 58 taste control using w/o/w emulsions, 58–59 transport and release mechanism of water-soluble components, 57–58 w/o/w emulsion instability, 56–57 w/o/w emulsion production, 56 Dough conditioners, 129 Droplet size distribution, 17, 18 Drug delivery via oral route advantages, 180 buccal delivery, 178 disadvantages, 180–181 local oropharyngeal delivery, 178 periodontal delivery, 178 sublingual delivery, 178 Drugs, transport mechanisms of active transport, 179 endocytosis, 180 facilitated diffusion, 179 passive diffusion, 179 Duplex emulsions. See Double emulsions Effervescent tablets, 196 Electrostatic bridging, 45 Emulsion stabilization, 42–43 coalescence, 46 creaming /sedimentation, 43–44 flocculation, 44–46 Ostwald ripening, 47 Emulsions delivery of hydrophobic food actives, 59–65 delivery of water-soluble food actives, 53–59 dietary fats delivery, 65–69 formulation design for food, 47–52 future trends, 69–73 release triggers, 52–53 stabilization, 42–47

Emulsions and micellar systems, encapsulation in, 7–8 Emulsions systems, 41–42 Encapsulants. See Core materials Encapsulated particles (bakery applications), properties for adhesion and cohesiveness, 125 film thickness, 125 flexibility, 124 good barrier properties, 124 mechanical strength, 125 melting properties, 125 particle size distribution, 125 surface morphology, 125 Encapsulated probiotics in dairy products (practical applications) cheese, 106 frozen desserts, 106–107 yogurt, 106 Encapsulating agents. See Wall-forming materials Encapsulation, 83–84, 135 Encapsulation, reasons for controlled release, 225 processability, 225 protection, 224–225 taste masking, 225 Encapsulation and controlled release in bakery applications antimicrobial agents, 129–130 chemical leaveners, 127–129 dough conditioners, 129 flavors, 130 sweeteners, 130 yeasts, 125–127 Encapsulation process extrusion, 3–5, 84–85 spray drying, 3–4, 5, 84 Encapsulation technologies for bakery applications high-pressure congealing, 117–118 hot melt particle-coating technology, 113–115 spray congealing, 116–117 Encapsulation technologies in food applications (marketing perspective) business promotion strategies, 239


Index

client communication, 223 costs associated with use of microencapsulation, 222 cross-fertilization of technology within the organization, 240 identification of high-volume end uses, 223–224 identification of technology potential, 224 manufacturing high-volume products, 223 new applications identification, 222 product proposal strategies, 239–240 technical expertise to other organizations, 241 technical innovation, 222–223 technique differentiation, 223 technique potential awareness, 222 Endocytosis, 180 Enzymatic covalent cross-linking, 45–46 Enzymes, encapsulation and controlled release of food, 139–140. See also Phytochemicals Extrusion, 3–5 Facilitated diffusion, 179 Fat- or wax-based matrices, encapsulation in, 7 Fats and glycerides lauric acid group, 120–121 oleic/linoleic acid group, 121 palmitic acid group, 121 Flavor encapsulation, 149–150. See also Complex coacervation Flavor-loaded microcapsules, 149–150 Flavors, 130 Flocculation, 44 bridging, 45–46 depletion, 44 Fluid bed coating, 113–116 Food actives – delivery via emulsions double emulsions for controlling water-soluble actives, 55–59 effect of o/w emulsions on taste release and perception, 53–55 water-in-oil emulsions for controlling water-soluble actives, 53 Food emulsions, formulation design for, 47–48 aqueous phase design, 48–49 choice of lipid phase, 49–50 interfacial formulation and design, 50–52

237

Food packaging, microencapsulation in future trends, 218 microencapsulated actives for packaging applications, 210–215 microencapsulated pigments, 215–217 Freeze drying, 5 Gellan gum, 91 Genetic Algorithms, 104 High-pressure congealing, 117–118 Hot melt coating (film-forming materials), 118–119 fats and glycerides, 120–121 glycol polymers, 120 resins and rosins, 120 waxes, 119–120 Hot melt extrusion, 4 Hydrogel matrices, encapsulation in, 8–9 Hydrophobic food actives – delivery via o/w emulsions aroma release, 60–63 lipophilic health ingredients, 59–60 structured emulsions in hydrogels for aroma release, 63–65 Hydrophobicity, 122 Incomplete surface coverage bridging, 45 Karmat Coating Industries Ltd., 232 κ-Carrageenan and locust bean gum, 91 Lozenges, 190 as delivery systems for dry mouth relief, 191–192 as delivery systems for teeth remineralization actives, 192 for delivering flavors and sensates, 190 for delivering throat relief actives, 191 vs. chewing gum delivery profile, 189–190 Lutein and leutin ester, 27 bioavailability, 27 role in age-related-macular degeneration, 26–27 solubilization, 29

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Index

Lycopene, 19 bioavalaibility, 20 formulation as additive in food systems, 20 hydrophilic–lipophilic balance of surfactant, 23–24 solubilization capacity, 20–23

Nonsoluble nutraceuticals, solubilization of, 17–19 lutein and lutein ester, 26–28 lycopene, 19–24 phytosterols, 24–26 vitamin E, 28–30 Nutraceuticals in nanosized self-assembled liquid (NSSL) vehicles, 13–17 bioavailability, 31–34 oxidative stability, 30–31 solubilization of, 15 solubilization of nonsoluble. See Nonsoluble nutraceuticals, solubilization of U-type microemulsions, swollen micelles, and progressive and full dilution, 17 water binding, 34–35

Micellar systems, encapsulation in, 7–8 Microcapsules, manufacturing of, 4–5 Microemulsion, 13, 30 formulation and characterization, 14–15 industrial applications, 13–14 phase diagram, 13–14 Microencapsulated actives for packaging applications antimicrobial food packaging materials, 210–212 insect and/or rodent repellent food packages, 212–213 scented fragrance-inserts and flavorreleasing systems, 213–215 Microencapsulated flavors market, 235–237 Microencapsulated food ingredients, 224 competitive factors, 233–234 industry structure, 230–233 key end-user groups, 233 market drivers, 226–227 market restraints, 228–229 pricing, 229–230 Microencapsulated pigments, 215–216 inks and time–temperature indicators, 216–217 Microencapsulated probiotics market, 237–238 Microencapsulated salts and acids market, 237 Microencapsulated vitamins market, 237 Microporous matrices, encapsulation in, 7 Molecular sieve, 7 Monodispersed emulsions, 73 Mucoadhesion, 192

Oil-in-water microemulsions, 18 Oral cavity. See also Drug delivery via oral route; Oral transport routes, physiological and structural basis of division, 172 esophagus, 173–174 permeability and barrier functions, 174 tongue, 173 trigeminal nerve, 174 Oral delivery routes local, 172, 181 systemic, 172, 181 Oral transport routes, physiological and structural basis of epithelial membranes, 175 keratinization, 177 membrane coating granules, 177 oral mucosa, 175 pH, 178 plasma membranes, 174–175 polarity, 177–178 saliva, 176–177

Nanoemulsions, 143–144 Nanoparticles, 144 Nature-made emulsions oil or lipid bodies, 69–71 plant cells, 72 yeast cells, 71–72

Paraffin wax, 119 Particle Coating Technologies, 233 Particle Dynamics, Inc., 232–233 Passive diffusion, 179 Payload, 2 Phase diagram, 13–14, 16


Index

Physical release, 225 Phytochemicals bioconjugation, 144 encapsulation and controlled release, 140–143 encapsulation by nanoemulsion, 143–144 Phytosterols chemical structure, 24–25 solubilization capacity, 25–26 Plasticizers, 123 Pressed tablets, 196 Probiotic capsules, manufacturing conditions for encapsulating according to experimental design, 98–99 optimal manufacturing conditions verification, 105 optimization using genetic algorithms, 104–105 optimization using SDP technique, 101–104 performing optimization, 101 response surface models and optimization model formulation, 99–101 screening experiments and experimental design, 96–98 Probiotic encapsulation techniques in dairy products advantages and disadvantages, 87–89 emulsion, 85–87 extrusion, 84–85 spray-drying, 84 Probiotic survival (effect of encapsulation) in dairy products effect of carrier matrix, 89–92 effect of spray drying, 92–93 in dairy products, 93–94 in gastrointestinal conditions, 94–96 Probiotics, 83 Protein/polysaccharide coacervation, 136–139 Release mechansisms burst, 10–11 combination, 10 matrix systems, 9–10 reservoir-type systems, 9 Release modes, 225

Release rates, 10–11 Release triggers, 2 for emulsions, 52–53 Release delayed, 1 sustained, 1 SDP method, 101–104 Seamless capsules, 194–196 Shellac resin, 119 Solid fat index, 122 Solubilization capacity, 24 Solubilization efficacy, 24 Spray congealing, 116–117 Spray dryers, 117 Spray drying, 3–4, 5, 84 Steroid alcohols. See Phytosterols Surfactants, 13 polysorbates and sugar esters, 15 Sweeteners, 130 TasteTech, 233 Thermal release, 225 U-type microemulsions, 17 U-type phase diagram, 16, 17 Vitamin E, 28 solubilization capacity, 28–30 Wall-forming materials, 1–2 Water binding, 34–35 Wax- and fat-coating material, characteristics of chain length, 121 degree of unsaturation, 121 hydrophobicity, 122 melting point, 123–124 polarity, 121 polymorphism, 122–123 solid fat index, 122 Wax macro-microemulsions, 120 Xanthum gum, 91 Yeasts, 125–127

239

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Encapsulation and Controlled Release Technologies in Food Systems, 0813828554

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