浙大食化考研

Chapter4LipidsKeypointsLipidoxidationEmulsion11/49FoodLipidsDefinition:Nonpolar,hydrophobic,poorlywatersolublecomponentswhicharesolubleinorganicsolventssuchasalkanes(e.g.hexane)Includes fats: solidatroomtemperature

oils: liquidatroomtemperatureDefinitionbasedonphysicalpropertiesTriglyceridesFattyAcidsPhospholipidsTerpenes/Terpenoids(萜類化合物）Steroids（類固醇o(jì)r甾族化合物）WaxesPrimarytopicsforFST22/49StructureofPhospholipid33/49PhospholipidPropertiesPhosphatide“headgroup”ispolar,chargedhydrophilicFattyacid“tails”arenonpolarhydrophobicMoleculethushassplitcharacterAmphiphilic(MoleculesaresurfaceactiveSitbetweenhydrophilicandhydrophobicphasesPXoilwaterPXairwater44/49ImportantFoodFattyAcidConstituentsD9,1255/4966/49FatContentofSomeFood77/49AttributesofFoodLipidsThreemajorfunctionsinfoodsEnergyandhealth(Biochemistry,FoodNutrition)Influencefoodflavorsfreefattyacidscontributeflavorslipidsactassolventsforcarryinghydrophobicflavorsandaromas(andnutrients)InfluencefoodTextureSolidvsliquidMixedwithwater(emulsions)Attributesdeterminedbytypesandpositionsoffattyacidsonglycerolbackbone88/49FoodFattyAcidConstituentsMostfoodfattyacidsEvennumberofcarbonsLinear(notbranched)DoublebondsinnaturearecisEventhoughtransdoublebondsareinlower

energystate99/49PlantTriglyceridesCocoabutter~equalC16:0,C18:0,C18:1sn-2primarilyunsat’dsn-1,3largelysat’dSSU66%USU20%(BelitzandGrosch,1999;?Springer-Verlag.)1010/49PlantTriglycerides

coconutandpalmkernel

Coconut,palmkernelrichinC8:0-C14:01111/49PlantTriglyceridesPeanutOil~40%oleic;40%linoleicsn-2largelyunsat’dSUUUUUSoybeanoilsimilar(BelitzandGrosch,1999;?Springer-Verlag.)1212/49PlantTriglyceridesOliveOil~75%oleicsn-299%unsat’dhomogeneousUUU(BelitzandGrosch,1999;?Springer-Verlag.)1313/49PlantTriglycerides1414/49GeneticsInfluenceonErucicacidofrapeseed1515/49AnimalTriglyceridesBeefFat~equalC16:0,C18:0,C18:1sn-2bothsat’d&unsat’dsn-1,3bothsat’d&unsat’dSUUUUSSSU(BelitzandGrosch,1999;?Springer-Verlag.)1616/49AnimalTriglyceridesPigFat(Lard)~equalC16:0,C18:0,C18:1sn-2largelysat’d

sn-1bothsat’d&unsat’dsn-3largelyunsat’dSUSUUSUSU36%29%12%UUU15%(BelitzandGrosch,1999;?Springer-Verlag.)1717/49AnimalTriglyceridesMilkFat-Largenumberofshort-chainfattyacidsaffectscheeseflavorcausesmilkrancidityMarineOilsLong-chainunsaturatedfattyacids(Coultate,1989;?RoyalSocietyofChemistry)EPADHAEicosapentaenoicacidDocosahexenoicace1818/49SummaryofFattyAcidProfilesPlantfats/oils:sn-2largelyunsaturatedfattyacid(C18:1&C18:2)someplantoilscontainhighunsaturatedfattyacidcontents(peanut,soybean,olive,Canola)otherplantoilssignificantlysaturated(cocoabutter)coconutandpalmkerneloilprimarilysaturated—richinC8:0-C14:0Animalfats/oils:broaderrangeoffattyacids/triglyceridesfoundmilkfat(shortchains)vsfishoils(long,polyunsat’d)sn-2oftensaturated,greatervariationinpositions1919/49FlavorsinLipidsTriglyceridesactasnonpolarsolventsforhydrophobicflavorsandnutrientsAffectrateofreleaseFattyacids(releasedfromtriglyceridesbyhydrolysis)contributebitterorsoapyflavorsCauserancidflavorsinmilkStrongflavorsincheese(e.g.Rochfort)LipidoxidationreactionsproduceflavorsSmellyfishRe-friedfat2020/49FlavorsinLipids:FattyAcidsShorter-chainfattyacids(C4-C12)arefoundonlyincoconut/palmkerneloilsandinbovinemilkFattyAcid4:06:08:010:012:014:016:0FlavorCharacteristicsrancidrancid,likegoatmusty,rancid,soapysoapysoapysoapyThresholdConcentration(mg/kg)5085200>400>400>400notdetectable

theshorterthechain,thestrongertheflavor(BelitzandGrosch,1999;?Springer-Verlag.)2121/49LipidTextureTextureSolidvsliquidMixedwithwater(emulsions)

Strongeffectsofchainlengths,degreeofsat’n,andpositionoliveoilbutterormargarinechocolatewholemilk(4%fat)skimmilk(0%fat)2222/49LipidMelting/Crystallizationsolidifies(crystallizes)moreeasilyLipidswhichcrystallizemoreeasilyrequirehighertemperaturestomeltM.P.=temperatureforcrystallization/meltingofmoleculeFoodlipidsaresolidsandliquidsAsintermolecularattraction

strengthensorentropy(熵）weakens2323/49EffectofFattyAcidGroupsLongerchainfattyacidspackbetterthanshorterchainsM.P.long>M.P.shortSaturatedfattyacidspackbetterthanunsaturatedM.Psat’d>M.P.unsat’dTransfattyacidspackbetterthancisM.Ptrans>M.P.cishydrogenationincreasesM.P.-OOC-OOC-OOCsat’d transunsat’dhigherM.P.moresolidcisunsat’dH22424/49TriglycerideMixturesFoodfats/oilscontainmixtureoftriglyceridesmixtureofcrystallizationproperties

rangeofmeltingtemperaturesatgiventemperature,foodlipidsoftenpartiallyliquid,partiallysolidbutter,margarinepeanutbutterOPOOOOPPStStStStOStPStPPvs.2525/49locationsoffattyacidsintriglyceridediffercocoabutter

lardCocoaButtervsLardComparecocoabuttervslard(pigfat)fattyacidcompositionquitesimilarroughlyequalC16:0,C18:0,C18:1Cocoabutterhomogeneous:meltssharplyatbodytemp;Lardheterogeneous:solid/liquidoverwidetemprangeSSUUSU66%20%SUSUUSUSU36%29%12%UUU15%2626/49EffectofFattyAcidPositionscocoabuttermeltscleanlyovernarrowTrangenearbodyTlardsolid/liquidmixtureoverbroadTrangegreasycompletelyliquid2727/49LipidOxidationLipidoxidationoccursbyafreeradicalchainreactionCO-O-CHH+H?CO-O-CH?RepresentasRH R?+H?containsanunpairedelectron2828/49PhasesofOxidationReactionThreephasesofreaction:InitiationRH R?+H?Propagation(傳輸）R?+O2

ROO?ROO?+RH ROOH+R?TerminationROO?+ROO? stable productsChainreaction--veryrapid;self-perpetuatingSlowNeedshighlevelsoffreeradicalsorlowO2RH:lipidROOH:hydroperoxideROO?:peroxidefreeradicals+R∑2929/49HydroperoxideDecompositionHydroperoxidesonlyweaklystable-O-O-bondeasilybroken7891011OOH7891011O?+?OH78O10?CH11+Aldehyde(醛）)10CH11Oaldehyde3030/49InitiationandPropagationOverviewThreemechanisms:Singlet（單線態(tài)）Oxygen(photooxidation)Lipoxygenase(脂氧合酶)MetalsOncefreeradicalsbuildup,reactiontakesoff!PropagationChainreaction(autocatalytic)3131/49OxidationProductsHydroperoxide----thefirstproductofoxidationHydroperoxidedecompositionleadstoaldehydeformation，ProducesrancidflavorsBad(rancid)smellsHydroperoxideswasusedtomonitorextentofoxidation3232/49FactorsthataffectlipidsoxidationAmountofoxygenpresentDegreeofunsaturationofthelipidsPresenceofantioxidantsPresenceofprooxidants(氧化強(qiáng)化劑）,especiallycopper,andsomeorganiccompoundssuchasheme-containingmoleculesandlipoxidase（脂氧化酶）NatureofpackagingmaterialLightexposureTemperatureofstorage3333/49OxidationRates:TypesofFattyAcidsAsthenumberofdoublebondsincreasesRateofReactionincreasesTypeofFattyAcid18:018:1D9

18:2D9,1218:3D9,12,15RateofReactionRelativetoStearicAcid1100120025003434/49OxidationRatesFreefattyacidsreactfasterthantriglyceridessn-2reactmoreslowlythansn-1,3UnsaturatedtriglyceridesoxidizefasterFishdeterioraterapidlyLinolenichydrogenatedinsoybeanoilPreventranciditySaturatedtriglyceridesstableatroomtemperatureOxidationacceleratedduringfrying(180?-200?C)OxidativeodorsovertimeHydrolysisproducesfreefattyacids,foaminess3535/49DelayingphotooxidationStoreoilsindarkOpaquecontainersDeactivatelipoxygenaseenzymesblanchingChelatingagents(EDTA,citricacid)AntioxidantsSubstanceswhichslowoxidationPreventionofLipidOxidationMilk3636/49AntioxidantsSubstanceswhichslowoxidationratesTwopossiblemechanisms:Quenchsingletoxygen1O2

3O2E.g.b-caroteneandascorbicacidSlowpropagationquencher3737/49AntioxidantsMostantioxidantsslowpropagationCompeteforfreeradicalsROO?RH ROOH+R? propagationAH ROOH+A? competitionantioxidant

GoodantioxidantsneedtoEasilyformfreeradicals AH A····HFormstablefreeradicalsBreakthechainreaction3838/493939/49PrimaryAntioxidants---FreeRadicalTerminators

SecondaryAntioxidants:

---Reducingagentsor"oxygenscavengers"

4040/49MechanismofPhenolicAntioxidants

Formresonance（共振）

structuresstableradicalsOftenoil-soluble(hydrophobic)duetoRgroupsOHORO?OROOROOR??4141/49StructureofphenolicantioxidantsManyantioxidantsarephenoliccompounds4242/49OxidationinBiologicalSystemsBeneficialandharmfuloxidationreactionsoccurinvivoPlants/animalscontainnaturalantioxidantsPreventharmfulreactionsOxidativedamagemaybelinkedtodiseaseAtherosclerosis(動(dòng)脈硬化癥）,cancer,aging,arthritis（關(guān)節(jié)炎）AntioxidantsupplementssoldEffectivenessdependsonsiteofactionCanbeprooxida