Starch Gelatinisation 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. Typical Corn vs Optimum® High Oil Corn Typical Corn OPTIMUM HOC Endosperm: Embryo: Starch Rich in Oil •Advantages of HOC •More Energy •Easier Processing Cross section of the vitreous part of a kernel, showing the polygonal shape of the starch granules, the indentation in the starch, and the tight compact structure. Cross section of the opaque part of a kernel, showing the spherical shape of the starch granules, the protein, and the large amount of air space. 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 Starch Structure Sugar chemistry Monosaccharides such as: Mannose ALPHA-D-GLUCOSE Galactose OH H 6 H Frucose H 5 H O Glucose 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: Prebiotic 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 and Pasting Grain sources categorized by rate of ruminal starch digestion. Adapted from Stock and Britton (1993). Gelatinization Temprature of a selection of ingredients Temprature range at which Sorce of starch gelatinization occurs(°C) Barley 51-60 Wheat 58-64 Rye 57-70 Oats 53-59 Corn 62-72 Waxy Corn 63-72 Sorghum 68-78 Rice 68-78 ژﻻتینه شدن نشاسته فرآیندی که پیوندهای بین ملکولی ملکولهای نشاسته در حضور آب و حرارت میشکند و منجر میشود به اینکهه ملهپ پیونهدهای هیدروژنی )هیدروژن هیدروکسیپ و اکسیژن( آب بیشتری را به خود جذب نمایند. نفوذ آب سبب بهم ریختگی ساختمان نشاسته شده و تعداد و اندازه ملپ های کریسهتالی آن را کهاهم مهی دهد.مناطق کریستالی اجازه ورود به آب را نمی دهند. حرارت سبب می شود چنین مناطقی نفوذ پذیر شده، بطوریکهه زنجیهره های نشاسته شروع به جداشدن نموده و فرم غیهر بلهوری و بهی نظم نشاسته بوجود می آید. 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 یک گرانول نشاسته که حاوی آمیلوز خطی و آمیلو پکتین منشعب است گرانولهای خام و نپخته نشاسته گرانولها در اثر حرارت دادن مرطوب متورم می شوند Starch Gelatinization start of heating only has water absorbed onto granule surfaces Granules still clumping آمیلوز از گرانولها جدا میشود Starch Gelatinization At 40oC more water as absorbed and granules start to separate تعدادی از گرانولها متﻻشی می شوند ژﻻتینه و خمیری شدن کامپ میشوند Starch Gelatinization At 65oC more water as absorbed and granules start to rupture Starch Gelatinization At 70oC further rupture, leakage Gelation اکنون اگر این ژل را سرد کنیم به مناطق ارتباطی توجه کنید water water water water water water This is a starch gel Factors Affecting Gelatinization Main determinants of gelatinization: 1- Water content 2- Starch concentration 3- Nature of starch 4- Degrading enzymes 4- Other environmental factors Factors Affecting Gelatinization Main determinants of gelatinization: 1- Fat 2- Protein 3- Temperature 4- Hydrogen bonds 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 StalingStaling · 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. StalingStaling 1 to 5% of baked goods are lost Climate plays a role Storage conditions Staling Mostly ascribed to: Retrogradation Moisture exclusion (crystallinity) Brittle crumb Low temperature – speeds up the process Freezing – prevents staling Starch Gelatinization Starch Gelatinization Thanks for attention .