FOOD FOOD CHEMISTRY: CHEMISTRY:

Unit-2Unit-2StarchStarch

BYBY

DR BOOMINATHAN Ph.D. DR BOOMINATHAN Ph.D. M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE)M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE)

PONDICHERRY UNIVERSITYPONDICHERRY UNIVERSITY

III lectureIII lecture

8/August/20128/August/2012

Source: Collected from different sources on the internet and presented by Dr Boominathan Ph.D.

StarchStarch

Thanks to Dr. EricksonThanks to Dr. Erickson

Central Washington Central Washington University, USAUniversity, USA

What is it?What is it?

Complex carbohydrate made up Complex carbohydrate made up of two componentsof two components

Components:Components:– AmyloseAmylose– AmylopectinAmylopectin

Properties depend Properties depend on amounts of on amounts of the componentsthe components

Where is it found?Where is it found?

Roots/TubersRoots/Tubers– PotatoPotato– ArrowrootArrowroot– TapiocaTapioca

CerealCereal– CornCorn– Waxy cornWaxy corn– WheatWheat– RiceRice– Waxy riceWaxy 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)

AmyloseAmylose

Linear Linear component of component of starchstarch

Contains Contains 1,4-1,4-alpha-glucosidic alpha-glucosidic bondsbonds

Molecular Molecular weight: weight: less less than 0.5 millionthan 0.5 million

Can form Can form coils coils which will trap which will trap iodineiodine and turn and turn blueblue

AmylopectinAmylopectin

Branched Branched component of component of starchstarch

Contains Contains 1,4-1,4-alpha-glucosidic alpha-glucosidic as as well as well as 1,6-alpha-1,6-alpha-glucosidic bondsglucosidic bonds

Molecular weight: Molecular weight: 50-500 million50-500 million

Limited coiling Limited coiling causes causes purplish-purplish-red colorred color when when iodine addediodine added

Amylose vs. Amylose vs. AmylopectinAmylopectin Starches usually contain Starches usually contain more more

amylopectin than amyloseamylopectin than amylose Generally Generally roots/tubers contain roots/tubers contain

more amylopectinmore amylopectin than than cerealscereals Roots/Tubers: 80% amylopectinRoots/Tubers: 80% amylopectin Cereals: 75% amylopectinCereals: 75% amylopectin Waxy corn Waxy corn andand rice rice contain contain

virtually virtually all amylopectinall amylopectin

Starch CompositionStarch Composition

Starch % amylose % amylopectin Tapioca 17% 83% Potato ~20% ~80% Wheat 25-26% ~75% Corn 24-28% ~75 Waxy corn ~0% ~100% Hi amylose Rice

~ 75% 22%

~ 25% 78%

Starch GranuleStarch Granule

Made in the cytoplasm of plant Made in the cytoplasm of plant cellscells

Amylopectin forms in Amylopectin forms in concentric concentric circles circles with with amyose dispersed in amyose dispersed in betweenbetween

Held together by Held together by hydrogen bondshydrogen bonds The granule swells when heated in The granule swells when heated in

waterwater

Starch GranuleStarch Granule

FunctionsFunctions

GelatinizationGelatinization– Structure in baked productsStructure in baked products– Thickener in sauces, soups, and Thickener in sauces, soups, and

dressingsdressings DextrinizationDextrinization GelationGelation

– Pie fillingPie filling

GelatinizationGelatinization

When starch is heated in waterWhen starch is heated in water Hydrogen bonds break, Hydrogen bonds break, allowing water to allowing water to

enter the granule and the granule swellsenter the granule and the granule swells Amylose migrates out of the granuleAmylose migrates out of the granule H-bonding between H-bonding between water and water and

amylopectin increasesamylopectin increases Reduced free water changes the Reduced free water changes the viscosity viscosity

of the starch mixtureof the starch mixture, thickening it, thickening it

5 % Corn Starch, 30C 5 % Corn Starch, 50C

5 % Corn Starch, 60C 5 % Corn Starch, 70C

Gelatinization and Gelatinization and TemperatureTemperature Gradually thicken with Gradually thicken with

temperaturetemperature Can be heated to 100Can be heated to 100ooC without C without

much granule rupturemuch granule rupture If held at 95If held at 95ooC will implode and C will implode and

lose viscositylose viscosity

Gelatinization and Gelatinization and Type of StarchType of Starch

Best Best thickening thickening ability (TA)ability (TA): potato : potato starchstarch

Worst thickening Worst thickening ability: wheat starchability: wheat starch

More More amylopectin=TA amylopectin=TA more more translucent=more translucent=more stringystringy

Viscosity and Type of Viscosity and Type of StarchStarch

Gelatinization and Gelatinization and SugarSugar Used together in pie fillings and puddingsUsed together in pie fillings and puddings Sugar competes with the starch for water so Sugar competes with the starch for water so

less water available for gelatinizationless water available for gelatinization Delays gelatinization and decreases Delays gelatinization and decreases

viscosityviscosity Increases gelatinization temperatureIncreases gelatinization temperature The more sugar added, the longer the delayThe more sugar added, the longer the delay Disaccharides have a stronger effect than Disaccharides have a stronger effect than

monosaccharidesmonosaccharides

Gelatinization and AcidGelatinization and Acid

Used together in fruit pie fillings, Used together in fruit pie fillings, specifically lemon fillingsspecifically lemon fillings

Acid breaks down starch Acid breaks down starch molecules so the paste is thinnermolecules so the paste is thinner

Decreases viscosityDecreases viscosity Acid effect can be minimized by Acid effect can be minimized by

adding after gelatinization or adding after gelatinization or heating rapidlyheating rapidly

GelationGelation

As a starch paste cools, a gel is As a starch paste cools, a gel is formedformed

Free amylose molecules lose energy Free amylose molecules lose energy as the temperature decreases and as the temperature decreases and form hydrogen bondsform hydrogen bonds

The The bonds create a network that bonds create a network that holds the swelled granules in placeholds the swelled granules in place

Gelation and Starch Gelation and Starch SourceSource The The more amylopectin (less more amylopectin (less

amylose), the softer the gelamylose), the softer the gel Potato starchPotato starch=high =high

amylopectin=good thickening amylopectin=good thickening agent=agent=softsoft gelgel

Corn starchCorn starch=less =less amylopectin=less effective amylopectin=less effective thickening agent=thickening agent=strong gelstrong gel

Gelation and Other Gelation and Other EffectsEffects HeatingHeating

– If temp. too high, will burst, if temp too low, limited amylose If temp. too high, will burst, if temp too low, limited amylose releasedreleased

– Enough amylose needs to be released from the Enough amylose needs to be released from the granule without the granule burstinggranule without the granule bursting

– Moderate temperature and rate of heatingModerate temperature and rate of heating AgitationAgitation

– Agitation during cooling disrupts amylose networkAgitation during cooling disrupts amylose network– Should mix flavorings immediately after removing Should mix flavorings immediately after removing

from heatfrom heat– If stir while heating too much, will break up granules and get If stir while heating too much, will break up granules and get

weakened gel.weakened gel.

Gelation and Other Gelation and Other EffectsEffects Sugar (addition of)Sugar (addition of)

– Decreases gelatinization and Decreases gelatinization and amylose releaseamylose release

– Softer gelSofter gel Acid (addition of)Acid (addition of)

– Decreases gelatinization by Decreases gelatinization by hydrolysis of granuleshydrolysis of granules

– Softer gelSofter gel

Aging GelsAging Gels SyneresisSyneresis (happens due to aging and when cut a gel and (happens due to aging and when cut a gel and

water leaks out)water leaks out)– Loss of water from a gelLoss of water from a gel– Amylose molecules pull together, squeezing water Amylose molecules pull together, squeezing water

outout RetrogradationRetrogradation

– Realignment of amylose moleculesRealignment of amylose molecules– Heat breaks the H-bonds holding the amylose and lets Heat breaks the H-bonds holding the amylose and lets

them move within the gelthem move within the gel– Hydrogen bonds break and reform into more orderly Hydrogen bonds break and reform into more orderly

crystalscrystals– Can be reversed by gently heatingCan be reversed by gently heating– Examples: refrigerated pudding, stale breadExamples: refrigerated pudding, stale bread

DextrinizationDextrinization

When starch is heated without When starch is heated without waterwater

A higher temperature is reached A higher temperature is reached than with waterthan with water

Bonds break throughout the Bonds break throughout the starch forming dextrinsstarch forming dextrins

Genetically-modified Genetically-modified StarchesStarches Waxy starchWaxy starch

– High in amylopectinHigh in amylopectin– Used in fruit pies because thickens well, but does Used in fruit pies because thickens well, but does

not gel wellnot gel well– Have good freeze-thaw stabilityHave good freeze-thaw stability

High amylose starchHigh amylose starch– Amylose creates strong bonds to form strong gelsAmylose creates strong bonds to form strong gels– Used in edible films to coat foodUsed in edible films to coat food– Edible films used in cough drops, candy, coatings for Edible films used in cough drops, candy, coatings for

deep fried potatoes, produce, baked productsdeep fried potatoes, produce, baked products

How to compare How to compare starches?starches? Line spread test:Line spread test:

– Measures thickening powerMeasures thickening power– Poor heated starch into cylinder, lift Poor heated starch into cylinder, lift

cylinder and measure spread after cylinder and measure spread after specified time using concentric circlesspecified time using concentric circles

Universal Texture Analyzer:Universal Texture Analyzer:– Measures gel strengthMeasures gel strength

Percent sag:Percent sag:– Measures gel strengthMeasures gel strength– Measure molded gel height and compare Measure molded gel height and compare

to unmolded gel heightto unmolded gel height– Stronger gel=small % sag, weaker Stronger gel=small % sag, weaker

gel=large % saggel=large % sag

Modified StarchesModified Starches Physically or chemically modifying native Physically or chemically modifying native

starchesstarches Are used for specific applications in the Are used for specific applications in the

food industry, Why?food industry, Why? Native starches have undesirable Native starches have undesirable

qualities:qualities:– Poor processing tolerance to heat, shear and Poor processing tolerance to heat, shear and

acidacid– Poor texturesPoor textures– Do not store, hold, and freeze/thaw wellDo 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 Pre-gelatinized StarchesStarches Use:Use:

– Instant puddingInstant pudding Dehydrated gelatinized starchDehydrated gelatinized starch

– Heated so granule swells and then Heated so granule swells and then dehydrateddehydrated

– Swells when water added, no heat Swells when water added, no heat necessarynecessary

– Decreases preparation timeDecreases preparation time– Physical changePhysical change

Thin-Boiling StarchesThin-Boiling Starches

Use:Use:– Pass freely through pipesPass freely through pipes

Acid-hydrolyzed starchAcid-hydrolyzed starch– Hydrolyzes 1,6-alpha-glucosidic bondsHydrolyzes 1,6-alpha-glucosidic bonds– Amylopectin in smaller piecesAmylopectin in smaller pieces– Decreases thickening power, but Decreases thickening power, but

makes a strong gel because hydrogen makes a strong gel because hydrogen bonds form more readilybonds form more readily

Cross-linked StarchCross-linked Starch

Use:Use:– Increases storage time because of reduced Increases storage time because of reduced

retrogradationretrogradation (eg., refrigerated puddings) (eg., refrigerated puddings) – More stable at high temperature, with More stable at high temperature, with

agitation, and with acid additionagitation, and with acid addition– Salad dressings, baby foods, pie fillingsSalad dressings, baby foods, pie fillings

Cross-linked starch moleculesCross-linked starch molecules– Alter hydroxyl ends under alkaline conditions Alter hydroxyl ends under alkaline conditions

by acetic anhydride, succinic anhydride, or by acetic anhydride, succinic anhydride, or ethylene oxideethylene oxide

– Amylose doesn’t realign b/c altered hydroxyl group Amylose doesn’t realign b/c altered hydroxyl group doesn’t line up well. Cross-links amylosedoesn’t line up well. Cross-links amylose

Viscosity and Cross-Viscosity and Cross-linked Starcheslinked Starches

Resistant StarchResistant Starch

Small intestine is unable to digest, limited Small intestine is unable to digest, limited digestion in large intestinedigestion in large intestine

ClassificationsClassifications– RS1: trapped in cells (seeds/legumes)RS1: trapped in cells (seeds/legumes)– RS2: native starch (raw potatoes, bananas, waxy RS2: native starch (raw potatoes, bananas, waxy

maize)maize)– RS3: crystalline, non-granular starch (cooked RS3: crystalline, non-granular starch (cooked

potatoes)potatoes)– RS4: chemically modifiedRS4: chemically modified

Can contribute fiber to food without the fat Can contribute fiber to food without the fat that bran hasthat bran has

Takes up less water than other fiber, making Takes up less water than other fiber, making dough less stickydough less sticky

Smooth even textureSmooth even texture Less than 3 cal/gLess than 3 cal/g