MODULE 9
BIOCHEMICAL CHANGES During Baking
Classification of baked products products Bread including small baked products (rolls, buns)
Fine baked goods, including long term or extended shelf-life products such as biscuits, crackers, the cookies, etc.
Made entirely or mostly from cereal flours; moisture content on average 15% Addition of sugar, milk and/or shortening amounts to a total less than 10%. Made from cereal flours at least 10% of shortening and/or sugar, as well as other added ingredients. Moisture content is greatly reduced.
Bread Ingredients Wheat flour Yeast Salt Water
Major components: components Gluten Water-soluble fractions Starch Lipids
A good quality of loaf is obtained only when there is an optimized combination of constituents, ingredients, and processing ! Mixing
Dough Development
Fermentation
Oven Baking
Mixing and Dough Development
Mixing or stirring the wheat flour-water mixture until the dough is developed.
Flour particles become hydrated. Formation of a cohesive and elastic dough. Dough becomes resistant to extension. Incorporation of air into the dough.
When a a dough is is optimally developed developed all all the the protein and starch starch become fully fully hydrated hydrated. The longer longer the dough dough is is mixed, the more more resistant resistant to to extension extension it it becomes
Protein and Dough Development
Wheat flour must be high in both protein content and quality
Protein content: Affects mixing time ! Low-protein flours (<12%) require longer mixing times. Mixing time is also associated with the nature of gluten protein. Mostly with glutenin fraction! Gluten is composed of two fractions: GLUTENIN & GLIADIN.
Protein and Dough Development
Structure of Glutenin
It is composed of high-molecular-weight proteins with values reported from 150,000 to 3 million. A system of polypeptide subunits held together by disulfide bonds. Intra- & interpolypeptide disulfide bonds must be present in glutenin in a certain ratio to provide the necessary viscoelastic properties for bread baking.
Protein and Dough Development
Glutenin & Bread Making Quality
HMW Glutenin fractions give a high loaf volume. Those fractions also represent the insoluble glutenin. SDS-PAGE patterns of HMW subunits of glutenin highly correlate with breadmaking quality.
The Water-Soluble Fraction of Wheat Flour Proteins Pentosans Dialyzable fractions
Water solubles (3.5% (3.5%
dialysis
Precipitate (globulins)
Dialysate Supernatant (water solubles, 2.3%)
Centrifugate (denatured albumins albumins)
Soluble pentosans Glycoproteins
Supernatant (water solubles, 1.3%)
The Water-Soluble Fraction of Wheat Flour
Pentosans
It consists of a straight chain of xylose units with a branch point of arabinose sugars at 2,3 positions (arabinoxylan). Arabinogalactans covalently link to proteins (glycopeptide) which contains ferrulic acid. A unique property of water-soluble pentosans is their ability to form gels (increase in viscosity) in the presence of oxidizing agents such as Ferrulic acid. Contribution of pentosans to loaf volume is confusing!
Lipids in Wheat FLour Although lipids are minor components of wheat flour, they play an important role in bread making. Of particular interest are the polar lipids, which contribute to mixing requirements and loaf volume potantial. Nonpolar lipids such as stearyl esters, glycerides, and free fatty acids have detrimental effects. Polar lipids (phospholipids & glycolipids), on the other hand, are effective improvers in bread makingonly glycolipids with improving effect on loaf volume.
Lipids in Wheat FLour Lipid-protein interactions: Once flour is wetted with water and mixed into a dough, the free lipids become bound by gluten proteins. Of the polar lipids, glycolipids appeared to be bound to the gliadin protien hydrophilically and to the gluten proteins hydrophobically. Simultaneous binding of glycolipids to gliadin and gluten proteins contributes structurally to the gasretaining ability of the gluten proteins.
Lipids in Wheat Flour
Lipoxygenase enzyme addition has several functions in breadmaking.
Increase the amount of free lipids in the dough Destruction of essential fatty acids Bleaching of carotenoids ( a whiter bread crumb) Increasing the mixing tolerance and dough stability.
Lipids in Wheat Flour Polyunsaturated fatty acids
lipoxygenase
O2
β-carotene
Lipid hydroperoxides
Colorless compounds
• Enzyme oxidizes the flour protein gluten, resulting in improved crumb structure. • It is a coupled reaction related to the release of bound lipids and oxidation of thiol groups at hydrophobic binding sites in dough protein.
Lipids in Flour aqueous
nonaqueous
Polyunsaturated free lipid
Bound lipid
Lipoxygenase+O2
Hydrophobic binding sites in proteins
Hydrophobic binding
Coupled oxidation
Oxidized lipid intermediates
Inversion of lipoprotein micelle
Hydrophobic oxidized site in proteins Lipid hydroperoxides water
Displaced lipid Free lipid
Oxidized protein
Starch in Breadmaking
Water absorption Gelatinization Retrogradation
Important properties
Starch in Breadmaking
Water Absorbtion When starch granules are added to warm water they readily absorb water and swell. At gelatinization temperatures (>50oC) water absorbtion increase resulting the expansion of starch granule volume. Intact starch granules absorb only half of their weight of cold water compared to damaged starch granules, which absorb up to twice their own weight. Damaged starch amount is important as it increases the absorbed water amount (controlled by milling, wheat variety, protein content of flour, baking process)
Starch in Breadmaking
Gelatinization Loss of birefringence (typical maltese crosses) when starch in water suspension is heated. During baking process, partial gelatinization occurs as a result of limited availability of water. The starch granules swell and result in a change in a change in configuration which allows them to elongate during expansion of the gas cell. Thus starch granule is involved in formation of film surrounding the gas cells (crumb structure).
Starch in Breadmaking
Retrogradation
Physical change in starch from a gel-like state to a more crystalline structure. In fresh bread, starch is mostly amorphous but undergoes recrystallization during storage. Retrogradation takes place during aging of bread. Lineer fraction amylose chains and also amylopectin chains, to a lesser extent, undergo association through hydrogen bonding.
Fermentation During fermentation yeast undergoes anaerobic metabolism, producing carbon dioxide gas, which aerates the dough. Also it imparts flavor to the baked product. About 40% of total carbon dioxide gas produced by yeast fermentation retains in the proofed dough. The remaining 60% is lost during punching, molding, and proofing the dough. The increase in dough volume during baking (oven spring) primarily is attributed to the vaporization in ethanol, with a small amount contributed by water vaporization.
Baking The effectiveness of baking process is determined by heat, enzyme activity, water, starch, and protein content. Toward to the interior of dough, the temperature rises slowly because of poor conductivity of the dough. o At 60 C the starch is gelatinized: water amount is important o At 70 C various enzymes are inactivated. o Above 75 C, irreversible denaturation and rupturing of gluten proteins occur. Maillard reactions - flavor & color development
