Starch Gelatinization
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FOOD CHEMISTRY 3 Starch Gelatinisation, Retrogradation and its Relation to Staling Provider: Dr. Alireza Foroghi Starch Structure Dent Floury endosperm. More “open” in structure yet Crown opaquein appearance. Dent corn has about equal Vitreous endosperm. proportions of horny to Also called horneous, floury starch (compared corneous or hard endosperm. to popcorn w/ mostly Produces grits in dry horneous starch. milling. Tightly compacted and translucent. More of this starch in mature, high Pericarp(bran) test weight kernels. Germ scutellum and embryonic axis. Hilum or abscission layer. Germ will be bigger Also called blacklayer. in HOC at the expense Caused by collapse and of starch. For each 1% compression of several layers increase in oil, expect of cells at physiological 1.3% decrease in starch. maturity. Cool weather can cause premature BL. Structure of the Grain Kernel (Seed) • Endosperm – contains most of the starch • Germ – embryo or the sprouting portion of the seed – High in oil and protein – not good flour but it is good animal feed • Bran – seed coat and other layers Typical Corn vs Optimum® High Oil Corn Typical Corn OPTIMUM HOC Endosperm: Embryo: Starch Rich in Oil •Advantages of HOC •More Energy •Easier Processing Endosperm • Cells fill with starch granules • Starch granules are enveloped in a protein matrix which impedes digestion of starch • If we process grain to break open the granule, can increase the digestion of starch • Grains differ in rumen fermentability largely due to the nature of the endosperm and protein matrix surrounding the granules – Less difference in intestinal digestibility Starch Structure Sugar chemistry Monosaccharides such as: Mannose Galactose ALPHA-D-GLUCOSE OH Frucose H 6 H H 5 H Glucose O 4 1 OH O 3 2 AFRICAN PRODUCTS (PTY) LTD H OH Starch Structure Sugar chemistry Disaccharides such as: Sucrose Maltose Isomaltose Cellobiose Lactose Starch Structure Sugar chemistry Oligosaccharides – various functions such as: Probiotic Gas Functional Starch Structure Sugar chemistry Polysacharides: Starch – amylose and amylopectin Cellulose Hemicelluoses Pectins Starch Structure Amylose Starch Structure Amylopectin Starch Structure Natural Starch conformation Mixture of amylose and amylopectin Pure amylose not natural (only 85%) Waxy maize starch - amylopectin Starch Composition TYPE OF AMYLOSE % AMYLOPECTIN STARCH % MAIZE 26 74 WHEAT 25 75 RICE 17 83 POTATO 21 79 CASSAVA 17 83 WAXY MAIZE 1 90 HIGH AMYLOSE 70 30 Starch Configuration Configuration = 3D structure Not soluble in cold water Settles No adhesive power No binding capacity Starch Configuration To have the previous properties the starch slurry must be heated Starch Gelatinization Heating causes the following: Water absorption by amyloplasts Rupturing of the amyloplast Starch network formed Hydrated network with water pockets Point at which rupture occurs differs Gelatinization! Starch Gelatinization Molecular explanation: Heat = vibration of atoms Vibration = breaks hydrogen bonds Rupture and parting of starch strands Water trapped = increased viscosity Forming of hydrogen bonds = gels Starch Gelatinization Gelatinization only occurs with heat and water Dry heating = dextrinization پایان Starch Gelatinization 5% Corn starch = start of heating only has water absorbed onto granule surfaces Granules still clumping Grain Processing • Grains often processed prior to inclusion in feeds – Alters feeding characteristics in predictable ways Altering the Physical Form of Grains 1) Dry: - Whole slow 1) Decrease particle size - Ground - Pelleted 2) Increase intake - Rolled 3) Increase digestibility - Steam flaked - Meal fast 4) Increase starch availability Grain Processing Physical – interrupt the seed coat Expose grain to digestive enzymes Make more palatable Heating – starch swells and gelatinization occurs Granules burst Gelatinized starch is more digestible ***advantage of physical processing is with small, hard grains and/or thick seed coat grains *** advantage of heating is with less fermentable grains; corn and milo Methods: Dry Processing Grinding – hammer mill and screens – anywhere from coarse to fine particle size Creates considerable amounts of fines Problems with Fine Ground Feeds Dusty feed Wind loss Stomach ulcers in swine Acidosis in ruminants *** Therefore want a medium grind for swine and coarse grind for cattle *** Processing is expensive; it is usually more cost-effective when grains are expensive Methods: Dry Processing Dry rolling – pass between two rollers turning in opposite directions– get a crack or a coarse grind Can adjust closeness of the rollers for some adjustment of fineness of grind Corrugated rollers used to crush hull to increase starch digestibility Other Methods: Dry Processing Micronize – microwave to 300o F (especially done with milo) Roasting – 300o F – puffed grain Extruded – heat + pressure = ribbons or flakes Pellet (or cube) – grind, mix with binder and pass through dies of various sizes Can combine various feedstuffs Starch Gelatinization At 40oC more water as absorbed and granules start to separate • Starch gelatinization is a process that breaks down the intermolecular bonds of starch molecules in the presence of water and temperature and allows the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water. Penetration of water increases randomness in the general structure and decreases the number and size of crystalline regions. Crystalline regions do not allow water entry. Heat causes such regions to be diffused, so that the chains begin to separate into an amorphous form. This process is used in cooking to make roux sauce, custard, or popcorn. Starch Gelatinization At 65oC more water as absorbed and granules start to rupture Starch Gelatinization At 70oC further rupture, leakage Starch Gelatinization Starch Gelatinization Factors Affecting Gelatinization Main determinants of gelatinization: Water content Starch concentration Nature of starch Degrading enzymes Other environmental factors Factors Affecting Gelatinization Main determinants of gelatinization: Fat Protein Temperature Hydrogen bonds Modified Starches Pre-gelatinization e.g. Stygel T Cold-water soluble Partially gelatinised prior to milling and drying Modified Starches Acid treatment Faster gelatinization Weak, low-viscosity gels Liquid foods and soft gels Stycolor 80 – thins on long cooking Modified Starches Enzyme treatment Plant and fungal amylases -1,4 glycosidic bonds hydrolysed Thin boiling starches Modified Starches Cross-linking Opposite effect to acid and enzyme treatment Forms a viscous paste / gel Distarch adipate and distarch phosphate Modified Starches Substitution Groups are attached to hydroxyl groups Interferes with H-bond formation Acetyl, propyl and methyl groups Clear sols Phosphate: clarity, stability and viscosity Modified Starches Dextrinisation Heating dry, powdered starch with acid 100 – 200oC Hydrolysis and transglucosidation White dextrin and yellow dextrins Films, coating, binder (thin-boiling yellow dextrin 6008) Staling Usually ascribed to : Loss of moisture Retrogradation Staling Bread and buns become firm (high- moisture, yeast-raised products); Crusty loaves dry out; Crisp baked goods go soft (low-moisture products); Off-flavours develop. Staling 1 to 5% of baked goods are lost Climate plays a role Storage conditions Staling Mostly ascribed to: Retrogradation Moisture exclusion (crystallinity) thanksBrittle crumb for your Low temperature – speeds up the process attention Freezing – prevents staling.