Starch I Lecture Notes PDF

STARCH 1 NST 108A OBJECTIVES ¡ Describe the basic structure of starch, amylose, and amylopectin how chemical structure influences function in food sciences ¡ Understand gelatinization, pasting, gelation, and retrogradation processes COMPLEX CARBOHYDRATES ¡ CHO – carbon, hydrogen, oxygen ¡ Comp...

STARCH 1 NST 108A OBJECTIVES ¡ Describe the basic structure of starch, amylose, and amylopectin how chemical structure influences function in food sciences ¡ Understand gelatinization, pasting, gelation, and retrogradation processes COMPLEX CARBOHYDRATES ¡ CHO – carbon, hydrogen, oxygen ¡ Complex carbs: oligosaccharides and polysaccharides POLYSACCHARIDES ¡ >10 units ¡ Affects water movement by hydrogen bonding = Water trapper ¡ Contributes to flavor and texture of products POLYSACCHARIDE EXAMPLES ¡ Starch - storage form of glucose in plants ¡ Glycogen - storage form of glucose in animals ¡ Cellulose & hemicellulose - plant cell wall structure ¡ Gums and pectins - polymers of monosaccharides that are NOT glucose FIBER = INDIGESTIBLE POLYSACCHARIDES bond ¡ Whole, plant-based foods β ¡ Provide texture ¡ Humans do not have enzymes to digest fiber, pass through GI tract unchanged ¡ No calories, many health benefits glucoselevel cholesterol colon health POLYSACCHARIDES: STARCH ¡ Storage form of energy in plants make staten ¡ Very large chain of glucose molecules ¡ Amylose in plant starch ¡ Amylopectin ¡ Deposited in tiny, solid granules Cell wall 9Eur  0 STARCH more A breakdown E faster pburg ¡ Amylose: 1,4-∝ linkage ¡ Amylopectin: 1,4-∝ and 1,6-∝ linkage ¡ Linear ¡ Branched ¡ Soluble bulky STARCH GRANULES a starcheshave both amylose amylopectin ¡ Rings of amylopectin interspersed with amylose – both present ¡ Different plants: different sizes ¡ Rice = smallest // Potato = largest ¡ Swell when heated with water granule absorb mots STARCH CHARACTERISTICS & QUALITY 1. Thickening power 2. Translucency 3. Texture 4. Flavor release 5. Stability 6. Storage 7. Hydration vs. none FACTORS AFFECTING STARCH FUNCTIONALITY 1. Ratio of amylose to amylopectin 2. Size of granule 3. Length of amylose chains 4. Impurities 1. RATIO OF AMYLOSE TO AMYLOPECTIN all around water Amylose: tangles up around water and amylopectin to form a gel make ¡ More amylose = firmer gelation ¡ Longer chains = better for thickening water istrapped get Amylopectin: quickly absorbs water ¡ Influences faster gelatinization & thickening doesn'tme anthem is solid All (natural) starches contain both GELATINIZATION VS. GELATION ¡ Gelatinization – swelling of starch granules when starch is heated in water o ¡ Heat breaks hydrogen bonds in starch granules à water enters granule à water continues to enter causing granule to swell à ↑ water in granule, ↓ free water surrounding granule ¡ Some amylose leaves the granule for water surrounding it Twateris absomedblanks ¡ Water forms hydrogen bonds with amylopectin and amylose ¡ *unique to starches ¡ Influenced by amylopectin that leaves can make gelation amylose in free worker ¡ Gelation – formation of a gel: liquid dispersed in a solid (or a sol à gel when cooled) ¡ All liquid within solid structure ¡ Influenced by amylose makeup Starch % Amylose % Amylopectin Waxy maize 0 100 Waxy rice 2 98 Tapioca (cassava) 17 83 Potato 20 80 Arrowroot* 21 79 Rice 22 wration 78 I occurs Wheat 26 casore201 74 Corn 28 72 amylosed High-amylose corn 70 30 amylose to amylopectin ratio impacts functionality 2. SIZE OF GRANULE ¡ Largest = better water absorbing capacity à better gelatinization ¡ Potato – largest granule size à superior thickening ability absons water w o getting ¡ Roots tend to be better than cereal starches (potato, tapioca, arrowroot) ¡ Increased viscosity ¡ Cereal starches – smaller granules à inferior thickening ability lesseffective ¡ Cereals are less effective compared to roots (corn, wheat, sorghum, rice) ¡ Wheat is the least effective: flour is least effective due to impurities ex still has proteinsbrang ¡ More soluble but less viscous solution endosperm 3. AMYLOSE CHAIN LENGTH ¡ Impacts degree of gelation as mixture cools ¡ Amylose outside of granule in free water amults Your ¡ ↓ temperature = ↓ in energy trap get ¡ Amylose molecules form hydrogen bonds with each other in lower energy state ¡ Bonded amylose create solid matrix – becomes continuous phase ¡ Remaining free water and swollen starch granule are dispersed phase ¡ More amylose correlated with longer chain length and stronger gels ¡ Low amylose starches DO NOT form gels Last or T 4. IMPURITIES Examples: bran, dirt, protein, sediment ¡ Provide stability to granule – takes more energy to gelatinize ¡ Cloudy – not translucent ¡ Too many impurities interfere with gel formation ¡ Can also include other things in the starch like protein and fat  None Unadein low be made in lab NATIVE STARCHES (NATURAL FORM) 1. Stringiness, cloudiness 2. Overly viscous textures 3. Gelling when not desired 4. Swollen, broken granules leads to loss of viscosity, gummy texture lumpyTravy 5. Retrogradation and syneresis water weak d of loss gels likein crystaline in amylose restructuring candy MODIFIED STARCHES ¡ Modified from it’s native state by chemical or physical means ¡ “Waxy” usually contain 0% amylose ramayaked ¡ Pre-gelatinized starches: starches have been gelatinized and then dehydrated – “instant” gelation ¡ Cold-water swelling: pre-gelatinized – ex) cornstarch slurry ¡ Others: don't needs know details ¡ Thin-boiling starches – debranched amylopectin = thin sol & hot gel ¡ Oxidized starches – debranched amylopectin + alkaline = soft gel ¡ Starch phosphates – thickener with excellent stability and clarity OTHER FACTORS THAT INFLUENCE GELATINIZATION & GELATION 1. Temperature – Need to heat high enough for gelatinization & gelation but not too long Ian losegel matrix 1. Gelatinization – granules can implode = small fragments = decreased viscosity 2. Gelation – extended heating can break amylose starch chains into small fragments resulting in pasty texture (lumpy gravy) and weak gel 2. Agitation – reduce during gelation process (cooling) – agitation interferes with amylose matrix formation and gel strength Impact? When should these be added? OTHER FACTORS THAT INFLUENCE GELATINIZATION & GELATION 3. Other ingredients: § Sugar: gelatinization § G1: hygroscopic – competes with starch for water, higher temp and longer cooking times for gelatinization § G2: results in more tender gel and greater translucency gelation § Acid: can shorten amylose chains resulting in more tender gel § Egg: must be cooked to denature ∝ −amylase: amylose-digesting enzyme in yolk Impact? When should these be added? POTENTIAL ISSUES FOR GELATION ¡ Syneresis – with time, amylose molecules draw together and free water seeps out ¡ Retrogradation – rearrangement of amylose molecules into more crystalline structure reheat some bread ¡ Results in grittier texture, decreases quality w wet papertowel ¡ Can be undone with gentle heating – breaking amylose hydrogen bonds and allowing gelling process to happen again ¡ examples: old bread, puddings and gravies held in fridge for days ¡ Dextrinization – occurs when starch is heated without water; results in amylose and amylopectin splitting and shorter molecules ¡ Example: flour on breaded meat