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Starch

Starch. Megan Erickson Central Washington University. What is it?. Complex carbohydrate made up of two components Components: Amylose Amylopectin Properties depend on amounts of the components. Where is it found?. Roots/Tubers Potato Arrowroot Tapioca Cereal Corn Waxy corn Wheat

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Starch

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  1. Starch Megan Erickson Central Washington University

  2. What is it? • Complex carbohydrate made up of two components • Components: • Amylose • Amylopectin • Properties depend on amounts of the components

  3. Where is it found? • Roots/Tubers • Potato • Arrowroot • Tapioca • Cereal • Corn • Waxy corn • Wheat • Rice • Waxy rice

  4. Amylose • Linear component of starch • Contains 1,4-alpha-glucosidic bonds • Molecular weight: less than 0.5 million • Can form coils which will trap iodine and turn blue

  5. Amylopectin • Branched component of starch • Contains 1,4-alpha-glucosidic as well as 1,6-alpha-glucosidic bonds • Molecular weight: 50-500 million • Limited coiling causes purplish-red color when iodine added

  6. Amylose vs. Amylopectin • Starches usually contain more amylopectin than amylose • Generally roots/tubers contain more amylopectin than cereals • Roots/Tubers: 80% amylopectin • Cereals: 75% amylopectin • Waxy corn and rice contain virtually all amylopectin

  7. Starch Composition

  8. Starch Granule • Made in the cytoplasm of plant cells • Amylopectin forms in concentric circles with amyose dispersed in between • Held together by hydrogen bonds • The granule swells when heated in water

  9. Starch Granule

  10. Functions • Gelatinization • Structure in baked products • Thickener in sauces, soups, and dressings • Dextrinization • Gelation • Pie filling

  11. Gelatinization • When starch is heated in water • Hydrogen bonds break, allowing water to enter the granule and the granule swells • Amylose migrates out of the granule • H-bonding between water and amylopectin increases • Reduced free water changes the viscosity of the starch mixture, thickening it

  12. Gelatinization and Temperature • Gradually thicken with temperature • Can be heated to 100oC without much granule rupture • If held at 95oC will implode and lose viscosity

  13. Gelatinization and Type of Starch • Best thickening ability: potato starch • Worst thickening ability: wheat starch • More amylopectin=more translucent=more stringy

  14. Viscosity and Type of Starch

  15. Gelatinization and Sugar • Used together in pie fillings and puddings • Sugar competes with the starch for water so less water available for gelatinization • Delays gelatinization and decreases viscosity • Increases gelatinization temperature • The more sugar added, the longer the delay • Disaccharides have a stronger effect than monosaccharides

  16. Gelatinization and Acid • Used together in fruit pie fillings, specifically lemon fillings • Acid breaks down starch molecules so the paste is thinner • Decreases viscosity • Acid effect can be minimized by adding after gelatinization or heating rapidly

  17. Gelation • As a starch paste cools, a gel is formed • Free amylose molecules lose energy as the temperature decreases and form hydrogen bonds • The bonds create a network that holds the swelled granules in place

  18. Gelation and Starch Source • The more amylopectin (less amylose), the softer the gel • Potato starch=high amylopectin=good thickening agent=soft gel • Corn starch=less amylopectin=less effective thickening agent=strong gel

  19. Gelation and Other Effects • Heating • Moderate temperature and rate of heating • Enough amylose needs to be released from the granule without the granule bursting • Agitation • Agitation during cooling disrupts amylose network • Should mix flavorings immediately after removing from heat

  20. Gelation and Other Effects • Sugar • Decreases gelatinization and amylose release • Softer gel • Acid • Decreases gelatinization by hydrolysis of granules • Softer gel

  21. Aging Gels • Syneresis • Loss of water from a gel • Amylose molecules pull together, squeezing water out • Retrogradation • Realignment of amylose molecules • Hydrogen bonds break and reform into more orderly crystals • Can by reversed by gently heating • Examples: refrigerated pudding, stale bread

  22. Dextrinization • When starch is heated without water • A higher temperature is reached than with water • Bonds break throughout the starch forming dextrins

  23. Genetically-modified Starches • Waxy starch • High in amylopectin • Used in fruit pies because thickens well, but does not gel well • Have good freeze-thaw stability • High amylose starch • Amylose creates strong bonds to form strong gels • Used in edible films to coat food

  24. How to compare starches? • Line spread test: • Measures thickening power • Poor heated starch into cylinder, lift cylinder and measure spread after specified time using concentric circles • Universal Texture Analyzer: • Measures gel strength • Percent sag: • Measures gel strength • Measure molded gel height and compare to unmolded gel height • Stronger gel=small % sag, weaker gel=large % sag

  25. Modified Starches • Physically or chemically modifying native starches • Are used for specific applications in the food industry, Why? • Native starches have undesirable qualities: • Poor processing tolerance to heat, shear and acid • Poor textures • Do not store, hold, and freeze/thaw well

  26. Pre-gelatinized Starches • Use: • Instant pudding • Dehydrated gelatinized starch • Heated so granule swells and then dehydrated • Swells when water added, no heat necessary • Decreases preparation time • Physical change

  27. Thin-Boiling Starches • Use: • Pass freely through pipes • Acid-hydrolyzed starch • Hydrolyzes 1,6-alpha-glucosidic bonds • Amylopectin in smaller pieces • Decreases thickening power, but makes a strong gel because hydrogen bonds form more readily

  28. Cross-linked Starch • Use: • Increases storage time because of reduced retrogradation • More stable at high temperature, with agitation, and with acid addition • Salad dressings, baby foods, pie fillings • Cross-linked starch molecules • Alter hydroxyl ends under alkaline conditions by acetic anhydride, succinic anhydride, or ethylene oxide

  29. Viscosity and Cross-linked Starches

  30. Resistant Starch • Small intestine is unable to digest, limited digestion in large intestine • Classifications • RS1: trapped in cells (seeds/legumes) • RS2: native starch (raw potatoes, bananas, waxy maize) • RS3: crystalline, non-granular starch (cooked potatoes) • RS4: chemically modified • Can contribute fiber to food without the fat that bran has • Takes up less water than other fiber, making dough less sticky • Smooth even texture • Less than 3 cal/g

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