FOOD CHEMISTRY: Unit-2 Starch BY DR BOOMINATHAN Ph.D. M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE) PONDICHERRY UNIVERSITY III lecture 8/August/2012 Source: Collected from different sources on the internet and presented by Dr Boominathan Ph.D.

Starch Thanks to Dr. Erickson Central Washington University, USA

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

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

Amaranth starch (Bar: 1 µm) Arrowroot starch (Bar: 20 µm) Buckwheat starch (Bar: 5 µm) Cassava starch (Bar: 10 µm) Corn starch (Bar: 10 µm) Oat starch (Bar: 5 µm) Potato starch (Bar: 50 µm) Rice starch (Bar: 2 µm)

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

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

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

Starch Composition

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

Starch Granule

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

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

5 % Corn Starch, 30C5 % Corn Starch, 50C 5 % Corn Starch, 60C 5 % Corn Starch, 70C

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

Gelatinization and Type of Starch Best thickening ability (TA): potato starch Best thickening ability (TA): potato starch Worst thickening ability: wheat starch Worst thickening ability: wheat starch More amylopectin=TA more translucent=more stringy More amylopectin=TA more translucent=more stringy

Viscosity and Type of Starch

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

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

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

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

Gelation and Other Effects Heating Heating –If temp. too high, will burst, if temp too low, limited amylose released –Enough amylose needs to be released from the granule without the granule bursting –Moderate temperature and rate of heating Agitation Agitation –Agitation during cooling disrupts amylose network –Should mix flavorings immediately after removing from heat –If stir while heating too much, will break up granules and get weakened gel.

Gelation and Other Effects Sugar (addition of) Sugar (addition of) –Decreases gelatinization and amylose release –Softer gel Acid (addition of) Acid (addition of) –Decreases gelatinization by hydrolysis of granules –Softer gel

Aging Gels Syneresis (happens due to aging and when cut a gel and water leaks out) Syneresis (happens due to aging and when cut a gel and water leaks out) –Loss of water from a gel –Amylose molecules pull together, squeezing water out Retrogradation Retrogradation –Realignment of amylose molecules –Heat breaks the H-bonds holding the amylose and lets them move within the gel –Hydrogen bonds break and reform into more orderly crystals –Can be reversed by gently heating –Examples: refrigerated pudding, stale bread

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

Genetically-modified Starches Waxy starch 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 High amylose starch –Amylose creates strong bonds to form strong gels –Used in edible films to coat food –Edible films used in cough drops, candy, coatings for deep fried potatoes, produce, baked products

How to compare starches? Line spread test: 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: Universal Texture Analyzer: –Measures gel strength Percent sag: Percent sag: –Measures gel strength –Measure molded gel height and compare to unmolded gel height –Stronger gel=small % sag, weaker gel=large % sag

Modified Starches Physically or chemically modifying native starches Physically or chemically modifying native starches Are used for specific applications in the food industry, Why? Are used for specific applications in the food industry, Why? Native starches have undesirable qualities: Native starches have undesirable qualities: –Poor processing tolerance to heat, shear and acid –Poor textures –Do not store, hold, and freeze/thaw well * Poor processing to heat/shear/acid: due to granules bursting which decreases viscosity * Freeze/thaw: has to do with amylose binding

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

Thin-Boiling Starches Use: Use: –Pass freely through pipes Acid-hydrolyzed starch 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

Cross-linked Starch Use: Use: –Increases storage time because of reduced retrogradation (eg., refrigerated puddings) –More stable at high temperature, with agitation, and with acid addition –Salad dressings, baby foods, pie fillings Cross-linked starch molecules Cross-linked starch molecules –Alter hydroxyl ends under alkaline conditions by acetic anhydride, succinic anhydride, or ethylene oxide –Amylose doesn’t realign b/c altered hydroxyl group doesn’t line up well. Cross-links amylose

Viscosity and Cross-linked Starches

Resistant Starch Small intestine is unable to digest, limited digestion in large intestine Small intestine is unable to digest, limited digestion in large intestine Classifications 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 Can contribute fiber to food without the fat that bran has Takes up less water than other fiber, making dough less sticky Takes up less water than other fiber, making dough less sticky Smooth even texture Smooth even texture Less than 3 cal/g Less than 3 cal/g