食品化學(xué)課件英文版chapter 2

Chapter2-1Chapter2CarbohydratesChapter2-2KeypointsMaillardbrowningCaramelization(焦糖化）Gelatinization(糊化）Retrogradation（老化，凝沉）Chapter2-3Carbohydrates:DefinitionsandStructuresOHCCH3HCHHCHCH3COOHOHOHHOCH2OHOOHAliphaticmoleculesAromaticmoleculeOHFoodCarbohydratesincludesugars,starches,gums,fiber,...Chemicaldefinition:Aliphatic(脂肪族的）polyhydroxyaldehydesandketonesandtheirderivativesaliphatic:Openchainorganiccompoundsandthosecycliccompoundsthatresemblethem(i.e.notaromatic)Chapter2-4NomenclatureCarbohydratesconsistofsingleormultipleunitsknownasmonosaccharideorglycoseunits Categorizedbychainlength Chapter2-5%Sugaroftotalfruitweight(Fennema,1985;?MarcelDekker)Highinfructose;othersugarspresentalsoSugarsinFruitsChapter2-6SugarsinVegetables%Sugaroftotalvegetableweight(Fennema,1985;?MarcelDekker)Vegetableslesssweet,higherinsucroseChapter2-7SugarsinProcessedFoods%SugaroftotalfoodweightChapter2-8SugarsNaming: prefix=no.ofCatoms suffix:“ose”-indicatescarbohydrateTrioses Tetraoses Pentoses HexosesMonosaccharides:

aldosescontainanaldehydegroup

ketosescontainaketonegroupInfoodthemajormonosaccharidesugarsofinterestare:

1.Thealdoses

D-galactoseandD-glucose(infruits,honey)2.Theketoses

D-fructose (fruits,honeyandcornsyrup)Chapter2-9Insolution,asinglemolecule(e.g.D-glucose,D-fructose)caninterchangebetweenstraightandringformdifferentringsizes

and

anomeric(異頭的）isomersChapter2-10

OHgroupscanactasnucleophile,changingsizeofringChapter2-11Furanose:5membereredringsPyranose:

6memberedrings

Thereare2cyclicdiastereoisomers(非對映異構(gòu)體）

Anomers（端基異構(gòu)體）aand

aanomer reducinggrouponoppositefacetoCH2group

anomer reducinggrouponsamefaceasCH2groupie.OHgrouponC1ofaldoses,C2ofketosesChapter2-12

ForD-glucose(interconversion-mutarotation)Chapter2-13GenerallyonlyafewisomerspredominateStraightchainformpresentinverysmallamounts(<1%)!SugarIsomersinWateraabb(BelitzandGrosch,1999;?Springer-Verlag)Chapter2-14ThreemajorphysicalpropertiesOptical(旋光）activitySweetnessWater-bindingactivityphysicalpropertiesofsugarsChapter2-15ReactionsofMono-andDisaccharidesIsomerizationglucose fructosemannose(甘露糖）OxidationR-CHOR-COOHR-CH2OHR-COOHReductionsugarsugaralcoholsAcetal(乙縮醛）formationsugarglycoside（糖苷）OCCCCCCHOHOHH2OHOHOHHHHHcarbonylgroupiskeyChapter2-16BrowningReactionsMaillardbrowningreducingsugar+aminebrownpigments+flavorsCaramelizationsugar brownpigments+flavorshightempsNon-enzymaticInvolvesugarsDoesnotinvolvesugarsEnzymaticbrowningphenolics brownpigments+flavorspolyphenoloxidaseChapter2-17MaillardReaction:FirststepCarbonylgroupundergoesnucleophilicattackbyamineOCCCCCCHOOHOHH2OHOHHHHHHreducingsugarImine(亞胺）Catalyzedbyacid;waterproducedToomuchacidprotonatesamine,nucleophilicity

CH=N-RCCCCCHOOHOHH2OHOHHHHH+H2-N-RH++H2OamineChapter2-18ImineFormation:MechanismAcid-catalyzednucleophilicaddition:OCHOCH

-N-RH2

HOH2

H+C-N-RHH2O

CH=N-RH

WaterisgoodleavinggroupH2-N-R+OHCH-N-RHprotonmigrates

H+

CH=N-RimineChapter2-19MaillardReaction:AmadorirearrangmentimineCH=N-RCCCCCOHOHH2OHOHHHHHH+HOAmadoricompoundCH=N-RCCCCCOHOHH2OHOHHHHH+HOCH-N-RCCCCCOHOHH2OHOHHHHHHOC-N-RCCCCC=OOHH2OHOHHHHHHOH2-ProtonatediminecanisomerizeanalogoustomonosaccharideisomerizationChapter2-20OMaillardReaction:LaterstepsDeamination(lossofamine)andfurtherisomerizationleadstoseveraldicarbonyl(二羰基）compoundsveryreactivemanyproducts,e.g.5-hydroxymethyl-2-CH3CCCCC=OOHH2OHOHHH=OCCHCCHHOH2CC=OHfuraldehyde(糠醛,HMF)HMFdicarbonylHMF,Amadoriproductsusedtomonitorreactioncyclicproductspolymerizetoformbrown,insolublemelanoidins（蛋白黑素）Chapter2-21MaillardReaction:SummaryReactionbetweenreducingsugarandamineFructoselessreactivethanaldosesAminescontributedbyproteinsoraminoacidsMaillardbrowningcancauselossofessentialaminoacids(e.g.lysine)HeatingwillaccelerateBrowningfasterincookedfoodsOccursslowlyatmoderatetemperaturesChapter2-22MaillardReaction:SummaryReactionfastestatmoderatelyacidicpH(pH4-7)AcidcatalyzesfirststepToomuchacidprotonatesaminelessofanucleophileReactionfastestatmoderatewaterlevelsWaterpromotesmobilityofreactantsWaterparticipatesatlaterstagesinreactionToomuchwaterpushesreactioninreverseSugar+amine imine+waterExpectbrowninginstored,dehydratedorheatedfoodsChapter2-23MaillardReaction:EffectofwaterBrowningrate

aswater

Rate

0incompletelydryproductMaillardproductsmeasuredduringcarrotdryingat110?C

drying(WallerandFeather,1983;?AmericalChemicalSociety)Chapter2-24MaillardReaction:ConsequencesLeadstoniceflavorsandcolorsinmanyfoodsLeadstoundesirableflavorsandcolorsinmanyfoodsCancausedestructionofessentialaminoacidsEspeciallylysine

BeneficialBreadSoysauceMilkchocolateCoffeeCaramel

UndesirableDehydratedpotatoesEggpowderCornstarchDriedfoodsmilkFruitsRoasted,grilledmeatsChapter2-25MaillardReaction:PreventionRemovereducingsugarsorproteinsRemovealmostallwaterUsestrongacidKeeptemperatureslowAddsulfites（亞硫酸鹽）Blocksdicarbonylreactions(?)Chapter2-26CaramelizationAthightemperatures,sugarreactionsareacceleratedIsomerizationWatereliminationOxidationAllsugarsreact(donotneedreducingsugar)noaminesCaramelization(thermalposition)occursatHightemperatures(~200?C)Lowwatercontent/highsugarCaramelflavorsandpigmentsFormationofEnediols（烯醇）DicarbonylsChapter2-27Caramelization:Dehydrationmechanism

EliminationofwaterfromanenediolCCCCCCHOOHH2OHOHOHHHHH-OHCCCCCCH2O-OHH2OHOHOHHHHH-OH+H+CCCCCCOHH2OH-OHOHHHHH=OH2O,H+1.dehydration(elimination)2.isomerizationenediolCCCCCC-OHH2OHH-H--HH=O=OH--OHdicarbonylChapter2-28Caramelization:ConsequencesLeadstoniceflavorsandcolorsinmanyfoodsCaramel,coffeeBeveragecolors,Maltol(帶焦糖味并有苦味的物質(zhì))oneimportantflavor (producedbyMaillardreactions)Canalsoleadtoundesirableflavorsandcolors“burnt-sugar”smellOOHCH3OChapter2-29BrowningReactionsMaillardbrowningreducingsugar+amine

Caramelizationsugar+highheatEnzymaticbrowningPhenolics+O2+PPONon-enzy-maticDoesnotinvolvesugarsRaisins(葡萄干)winedriedmilkdriedeggscookedmeatscaramelmilkchocolatejuiceChapter2-30Example:Caramel（飴糖）CandyIngredients:Sweetenedcondensedskimmilk,Cornsyrup,Partiallyhydrogenatedcottonseedand/orsoybeanoil,Sugar,Whey,Calciumcarbonate,Salt,Artificialflavor,Lipolyzedbutterfat,MolassesMixtureheatedtohightemperatureSugarseconcentratedCooltosolidifyChapter2-31Example:CaramelCandyWhatformsofsugarareinthiscandy?Sucrose,cornsyrup,lactose,molasses(糖蜜）Whatbrowningreactionsoccur?Cornsyrup,lactose+milkproteins(skimmilk,whey)MaillardbrowningSucroseathighconcentrationandtemperatureCaramelizationHowdoescornsyrupDEaffectbrowning?HigherDEmorereducingends(freecarbonyls)greaterMaillardbrowningChapter2-32Example:CaramelCandyHowdoescornsyrupaffectcandyconsistency?SucrosecrystallizeseasilyCornsyrupretardscrystallizationduringcoolingKeepscaramelsoftChapter2-33Starch:AmyloseStarchisaglucosepolysaccharide(aglucan(葡聚糖）)Amyloseisalinearglucanwith

[1,4]glycosidiclinkages

MW~106Chapter2-34Starch:AmylopectinAmylopectinisabranchedglucanwith

[1,4]and

[1,6]linkagesGlycogen（糖元）

inanimalsverysimilar

MW~1-50￥107Chapter2-35StarchGranulesStarchmoleculesonlysolubleinwarmwaterAggregateinwateratroomtemperatureInnature,starchpackedintosolidgranulesball-likeorganizationCrystalline(水晶狀的）

regionsrichinamylopectinamylosespreadthroughoutorderedstructureisbi-refringent（雙折射）showsorderedpatternsinpolarized(偏振）light

Oat

Bean

Potato

Maize

Rye（黑麥）

Barley

Chapter2-36StarchSolubilityUponheating,starchgranuleswilldissolvelosecrystallinityatgelatinizationtemperatureobtainwaterwithdissolvedstarch,somesolidremnantsformpasteUponcoolingagain,amylosecrystallizesmostreadilycalledretrogradationresponsibleforbreadstaling（陳化，變味）fasteratlowertemperatures(e.g.inrefrigerator)!maypartiallycrystallizetoformgel(e.g.pudding)oatmealChapter2-37Starchgranulescontainbothlinearamyloseandbranchedamylopectin.StarchGelatinizationandPasting,andUglificationChapter2-38Raw,uncookedstarchgranulesheatedinwaterChapter2-39SwellingisevidentChapter2-40NoticelossofamylosefromthegranulesChapter2-41Gelatinizationandpastingarecomplete

Somegranuleshavecollapsed.Chapter2-42Nowwestarttocool.GelationChapter2-43Noticeareasofassociation.Thesearecalledjunctionzones.Chapter2-44Thispictureisnotyetcompleteaswehaven’taccountedforthewaterinthesystem.Chapter2-45waterwaterwaterwaterwaterwaterThisisastarchgelChapter2-46WATERThispictureignoresswollenandcollapsedgranules.Junctionzoneswillnaturallyenlargeovertimeorinresponsetoprocessessuchasfreezing.UglificationChapter2-47WATERWATERofSYNERESIS(脫水收縮）

thathasbeensqueezedoutofthegelstructureThetexturegetsveryuglywhenthishappens.Chapter2-48RetrogradationofStarch

WhyFrozenpiescanbesoggy（出水）

Overtimeamylosecrystallisesoutofstarchsolutionsor pasteloweringviscosity. Fastforfrozenproducts. Mustuseamylopectinrichstarchesfortheseproducts. (eg.somemaizevarieties)Chapter2-49

BreadandsimilarproductsDough

aand

amylasesbreakdowndisruptedstarchtosugarsYeastfermentssugarstogiveCO2(bakingsodaforsome)Breakdownofstarchgranulesduringcookingdependson temperature,oilcontent,watercontent -variedtogivedifferentconsistenciesofbread, Stalebread-retrogradationofstarchtocrystallineproductChapter2-50

Retrogradationandnutrition Crystallizedstarchnotaccessibletoamylasesinthegut (Unbrokenandresistantstarchgranulesalsonotavailable) crystallizedandresistantstarchshouldbeclassedasfibre. Potatoesandunripebananascontaincrystallinestarch Rawpotatoesandunripebananasarenotdigestible.

Chapter2-51CornStarchHydrolysisPartialhydrolysisofcornstarchGlucosesubunitslinkedby

[1,4](and

[1,6])bondsHydrolysisproducesglucose,maltose,largerMWmoleculescornsyrup(upto96%glucose)andotherproductsExtentofhydrolysismeasuredusingdextrose（葡萄糖，右旋糖）equivalentsvalue(DEvalue：以葡萄糖計(jì)的還原糖在糖漿中所占百分?jǐn)?shù)）)AsDE,moresugars,fewerpolysaccharidesAsDE,sweeterandlessviscousproductHOOHOHCH2OHOOOHOHCH2OHOOOHOHCH2OHOOOHOHCH2OHOOOHOHCH2OHOOOHOHCH2OHOOOHOHCH2OHOOOHOHCH2OHOOChapter2-52CornStarchProcessingCombineenzymesforbesteffectAcidhydrolysisalsousedcommerciallyProducts:maltodextrinsarepolysaccharideswithreducedmolecularweightDE<20notverysweet,thickenercornsyrupisproductwithhigherlevelsofglucoseandmaltoseDE>20sweet,lesseffectivethickenerChapter2-53

ReactionswithStarchDextroseEquivalenceBrowningReaction

Binding

Solubility

Sweetness

Osmolality

Viscosity/BodyingAgent

FreezingPointDepression

CrystalGrowthInhibition