食品科學(xué)專業(yè)英語閱讀練習(xí)

2/92LESSON1NUTRITIONWhatweeataswellashowmuchweeatdetermineournutritionstatustoanimportantextent,andinfluencedbyadiversityofexternalandinternalfactors.Thepersonwhowantstofinetheanswertothequestion"whatshouldIeatforgoodnutrition?”,mighteasilybecomelostinthemazeofinformationalcorridors,confusedbythewealthoftechnicalinformationprovidedbyscientistsormisleadbysimplisticanswersprovidedbythosewithproductstosell.Somewhereinbetweenissomereasonable,commonsenseinformationthatwecanusetoguideusourquestforsoundnutritionknowledge。Tobegin,weneedtolearnsomedefinitionsofcommonlyusednutritiontermsandfindoutwhatsortsofguidelinesareavailabletohelpusmeasurethequalityofourdietsandtodevelophealthfuleatingpatterns.NUTRITIONANDFOOD:DEFINITIONS

Thewordnutritionisoftenpairedwiththewordfoodbecausethetwogotogether.Theyareinterdependent,butnotinterchangeable.Foodmightbedefinedasanyediblesubstancethatprovidesnourishmentwhenconsumed.Itismadeupofmanynaturalingredientsallchemicalsthathavedifferentfunctionssuchasprovidingodor,flavor,color,andnourishment.Theingredientsthatgiveusnourishmentarecallednutrients.Thesenutrientsarecategorizedasfats,proteinscarbohydrates(sugarsandstarches),minerals,vitamins,andwater.Theyarecalledessentialnutrientsbecausewecannotgetalongwithoutthem.Weneedthemforenergy,forbuildingandmaintainingbodytissue;andforregulatingbodyprocessesthethreeessentialfunctionsoffoodsinthebody.Nutritionmightbedefinedastheprocesswherebyweobtaintheessentialnutrientsandusethemtomakemanyothersubstancesourbodiesneed,thisprocesswouldincludeeatinganddigestingfoodandabsorbingandusing,ormetabolizing,thenutrientsitcontains.Wecanobtainalloftheessentialnutrientsfromfood.However,itispossibletoobtainnourishmentwithouteatinganddigestingfood-if,forexample,thenutrientsareinjecteddirectlytoourveinsasinintravenousfeeding.Thus,itisthenutrientsthatareessentialandthefoodthatnormallyprovidesthem.Sincefoodisvital,weneedtoknowthenutritivecontentoffoods,whichonesarethebestsourcesofthevariousnutrientsandhowtocombinethemintoahealthfuldiet.Thetermgoodnutritionimpliesthatweareobtainingfromourfoodalloftheessentialnutrientsintheamountsneededtokeepourbodiesfunctioningandtomaintainoptimumhealth.Averysimplifieddefinitionofgoodnutritionmightbe"eatingtherightfoodsintherightamounts.”Theworkofnutritionscientistsinvolvesfindinginthebody,theamountofeachthatweneed,whathappeningswhenwereceivetoomuchortoolittleandaboutfoodanddied-whatfoodsweshouldeatandinwhatamount.Yetnutritionscienceinitsbroadestsensehasmanymorefacets:theinfluenceofsensoryfactorsofflavor,color,andtextureoffoodoneatingbehavior;thepsychological,cultural,emotional,andsocialaspectsoffoodintake;andeventheeconomicsoffoodavailabilityandconsumerbehaviorinthepurchaseoffoodTHENUTRIENTS

Todate,nutritionscientistshaveidentifiedsome40to45substancesasessentialnutrients.Butthelistisgrowingasnewnutrientscontinuetobeidentified;thehistoryofnutritionsciencecontainsfascinatingstoriesaboutthewaysfoodsubstanceshavebeenidentifiedasessentialnutrients.Insomeinstances,medicalresearchersseekingthecauseofaparticulardiseasefoundthatproblemwasduetoasinglesubstance,andthatwhenthissubstancewasaddedtothediet,thesymptomsofthediseasedisappeared.Anumberofvitaminswerediscoveredinthisway.Nutrientsmightbedividedintotwogenialcategoriesbasedontheamountthatweneed.Thesearethemacronutrients(carbohydrates,fats,proteins,andwater),whichweneedinrelativelylargeamountsandthemicronutrients)mineralelementsandvitamins),whichweneedinrelativelysmallamounts.Allofthenutrientsexceptformineralelementsandwaterareclassifiedasorganicchemicalsbecausetheycontaintheelementcarbon.Mineralelementsandwaterareinorganicchemicalsbecausetheydonotcontaincarbon.Thevitaminsaredividedintotwogeneralcategorizesbasedontheirsolubilityineitherwaterorfat.thefat-solublevitaminsarevitaminsA,D,E,andK;thewater-solublevitaminsincludevitaminsC(ascorbicacid),niacin,thiamin,riboflavin,flacon(alsocalledfolicacid)antitheticacid,pyridoxine,vitaminB12andbiotin.Themineralelementsaredividedintotwocategoriesbasedonthequantityofthemthatweneed.Microelementsarethoseneededinrelativelylargeamounts,whilemicroelementsarethoseneededinverysmallamounts,someexampleofmicroelementsaresodium,calcium,andphosphorus.Someexampleofmicroelementsisiron,iodine,manganese,zinc,andfluorine.

RECOMMENDEDDIETARYALLOWANCES

Onceanutrientisidentified,oneoftheprincipalresearcheffortsofnutritionscientististodeterminehowmuchofitisneededbypeopleatvariousagesandstagesoflife.Initialstudiesusuallyareconductedwithlaboratoryanimals,buttheinformationdevelopedinthesestudiescannotbeapplieddirectlytohumanssincepeople’sneedsoftenarequitedifferentfromanimals’needs.Humannutritionstudiesontheotherhand,aretime-consuming,costly,anddifficulttoconduct,especiallybecauseoftheproblemsofcontrollingvariablesandpossiblycausingharmtotheindividualsinvolved.Becauseoftheobstaclestocollecting,accuratedata,ourpresentknowledgeofnutrientneedsisincomplete,andtherequirementsofhumansformanynutrientshavenotbeenestablished.However,thedataonhumanandanimalneedscurrentlyavailableareusedbynutritionscientiststoestablishestimatesoftheamountsofessentialnutrientsperdaythatwillmeettheneedsofmosthealthpersons.IntheUnitedStates,themostwidelyusednutrientguidelinesaretherecommendeddietaryallowance(RDA),whichareissuedbythenationalacademyofsciences,nationalresearchcouncil,andfoodandnutritionboard.TheRDAservesasdietaryofnutritionalstandardsforawiderangeofage-weight-sexgroupssuchasinfants,children,adolescents,pregnantandlactatingwomen,andyoungerandolderadults.Theyarerecommendations,notaveragerequirements,forsatisfactorylevelsofintakeofessentialnutrientsofpopulationgroupsofaverage,healthypeople.Theydonottakeaccountofspecialneedscertainindividualsmayhaveduetogeneticmakeup,metabolicdisorders,chronicinfections,andotherabnormalities,whichmayresultintheirneedingdifferentlevelsofnutrients.

MARGINofSAFETYALLOWSforINDIVIDUALDIFFERENCES

Toallowforindividualdifference,theusuallyaresetwithagenerousmarginofsafety.Thus,theyarethoughttomeettheneedsof95to97percentofthepeoplewithineachage-sexgroup.Inotherwords,theRDAexceedtherequirementsofmostindividualstoensurethattheneedsofnearlyallaremeet.Forthisreason,apersonwhoconsumesadietthatprovideslessthantheRDAforoneormoreessentialnutrientsisnotnecessarilygettingadietthatisnutritionallyinadequate.Whatcanbeconcluded,however,isthatthefarthertheintakeofanessentialnutrientfallsbelowtheRDA,thegreatertheprobabilityofnutritionalinadequacy,ontheotherhand,ifanindividualisgettingalltheessentialnutrientsatorabovetheRDAlevelofhisorherage,chancesaregoodthatdietisnationallyadequate.AnexceptionistheRDAforenergyorcalories,whicharenotdesigned,asguidesforindividualcaloricneeds.OthervariablesnotincludedintheRDA,suchasbodysizeandphysicalactivity,areinvolvedinanindividual’scaloricrequirements

DIFFERENCESINNUTRIENTUTILIZATIONCONSIDEREDAnotherfactorconsideredwhentheRDAareestablishedistheavailabilityofthenutrientandfactorsthataffecthowefficientlyitisusedinthebodyforsomenutrients,suchasiron,absorptionoruseinthebodymaybeincomplete;sotheRDAneedstobesethighenoughtoallowforthis.Andbecauseinthecaseofcertainothernutrients,substancefoundincarrotsandothervegetablesandfruits,whichourbodiesconverttovitaminA.Ontheothersideofthecoin,receivingtoomuchofcertainnutrients,amountssignificantlyabovetheRDA,canbejustharmfulasnotobtainingenoughcertainvitamins(suchasAandD)andmineralscanbehighlytoxicifhighforoptimalnutrientintakefromthestandpointofbothmaximumandminimumlevels.LESSON2CARBOHYDRATES

Thefoodscientisthasamany-sidedinterestincarbohydrates.Heisconcernedwiththeiramountsinvariousfoods,availability(nutritionalandeconomic),methodsofextractionandanalysis,commercialformsandpurity,nutritionalvalve,physiologicaleffects,andfunctionalpropertiesinfoods.Understandingtheirfunctionalpropertiesinprocessedfoodsrequiresnotonlyknowledgeofthephysicalandchemicalpropertiesofisolatedcarbohydrates,butalsoknowledgeofthereactionsandinteractionsthatoccurinsitusbetweencarbohydratesandotherfoodconstituentsandtheeffectsofthesechangesuponfoodqualityandacceptance.Thisisatallorderforknowledge.Becauseprocessingaffectsbothnutritionalandestheticvaluesoffood,knowledgeofthechangesthatcarbohydratesundergoduringmilling,cooking,dehydration,freezing,andstorageisespeciallyimportant.StudentsareadvisedtostudythefundamentalchemistryunderlyingusefulcarbohydratespropertiesOfservicewillbeanunderstandingoftheassociationofpolarmoleculesthroughhydrogenbonding,ioniceffects,substituenteffects,chelationwithinorganicions,complexingwithlipidsandproteins,anddecompositionreaction.Thisbackgroundwillprovideanunderstandingofpropertiesthataffectthetextureandacceptanceofprocessedfoods(e.g.,solubility,hygroscopicity,diffusion,osmosis,viscosity,plastity,andflavorproduction),propertiesthatenabletheformationorhighqualitypastries,gels,coatings,confections,andreconstitutabledehydratedandfrozenfoods.Abilitytopredictwhatchangesinfunctionalpropertiesarelikelytoensuefromincorporatingvarioustypesofcarbohydratesintoprocessedfoodsisapracticalgoalofthefoodscientist.Suchforecastingrequireseitherawealthofexperiencewithtrial-and-errormethodsoradeepknowledgeofcarbohydratepropertiesasrelatedtostructure—perhapsboth.However,scientificknowledgeofcauseandeffectishighlyrespectedwhenitshortensindustrialdevelopmenttime

Source,Types,andTerminology

Thelayman’sconceptionofcarbohydratesgenerallyinvolvesonlythesugarsandstarchesoffoods—thosethatgeneratecaloriesandfat.Thefoodchemistknowsmanyothertypesthatareingested.Becausemostpeopleenjoythesweetnessofsugarsandthemouthfeelofcookedstarches,theybecomefamiliarbyassociationwithtablesugar(sucrose),invertsugar’shydrolyzedsucrose,cornsyrupsugars(D-glucoseandmaltose),milksugar(lactose),andthemorestarchyfoods.Thesecarbohydratesarenutritionallyavailable;i.e.,theyaredigested(hydrolyzedtocomponentmonosaccharides)andutilizedbythehumanbody。Carbohydratesofdietaryfiber(cellulose,hemicelluse,pentosans,andpecticsubstances),incontrast,tendtobeoverlookedbecausetheyarelargelyunavailable.Digestiveenzymesdonothydrolyzethemsignificantly;nevertheless,theymaybequiteimportantforhumanhealth.Thecarbohydratesofnaturalandprocessedfoodsaredividedintoavailableandunavailabletypes.Theavailablecarbohydratesvaryindegreesofabsorptionandutilizationdependinguponquantitiesingested,accompanyingfoodtypes,andhumandifferencesincomplementsofdefectiveenzymesandintestinaltransportmechanisms.Malabsorptiondifficultiesandadversephysiologicaleffectsareknownforalltheavailablecarbohydratesbutgelatinizedstarchesgivelittleornotrouble.Itisimportanttorealizethatinruminantstheunavailableandmostabundantpolysaccharidecelluloseispartiallyhydrolyzedtothesamehighlyavailablesugarthatstarchprovidesupondigestion;i.e.D-glucose.Grazinganimalsdoitthroughthecellulosesgeneratedbythemicroorganismsoftheirrumen.Celluloseis,therefore,acontributingsourceofvolubleanimalprotein.Foodchemistsprobablycanimproveupontheefficiencyandeconomicsoftheruminant’sconversionofcellulosetonutrients.Developmentofcellulosesthatarestableoutsidethecellsofmicroorganismsenablestheculturingoffungiandwithyeastsoncellulosehydrolyzates.Fungi(e.g.,mushrooms)canproduceproteinwiththebiologicalvalueofanimalprotein.Theconversionofcellulosewastestoanimalfeedandhumanfoodisanintriguingprospectforlimitingenvironmentalpollutionandforfeedingtheworld’expendingpopulation.Carbohydrateswerefirstnamedaccordingtotheirnaturalsources;e.g.,beetsugar,canesugar,grapesugar,maltsugar,milksugar,cornstarch,liverglycogen,andsweetcornglycogen.Trivialnameswerethenformed,inEnglishterminology,oftenfromaprefixrelatedtothesourcefollowedbythesuffix“-ose”todenotecarbohydrate.Namesarisinginthisway,forexample,arefructose,maltose,lactose,xylose,andcellulose.Theseshort,well-establishednamesarestillcommonlyused.Theyfurnishnoinformationonthechemicalstructureshowever,soadefinitivecarbohydratenomenclaturehasbeendeveloped.Fromthedefinitivenames,structuralformulascanbewritten.Someofthetermsinvolvedinthedefinitivenomenclatureareexplainedinthefollowingparagraphs.Thesimplesugars(monosaccharides0arebasicallyaliphaticpolyhydroxyaldehydesandketones:HOCH2-(CHOH)n-CHOandHOCH2-(CHOOH)n-1-C-O-Ch2OH,called“aldoses”and“ketoses,”respectively.However,itmustbeunderstoodthatcyclichemiacetalsofthoseopen-chainformsprevailIsolidsandatequilibriuminsolutions.Inthedefinitivenomenclature,thesuffix“ose”isappendedtoprefixesdenotingthenumberofcarbonatomsinthenomosaccaride;e.g.trioses(n=1),tetroses(n=2),pentoses(n=3),hexoses(n=4)todistinguishaldosesfromketoses,ketosesaredesignatedas”-uloses.”Thus,thesimplestketose,HOCH2-C:O-CH2OH,isatriulose;themostcommonketose,D-fructose(levulose),isahexlose.Todesignatetheconfigurationsofhydroxylgroupsontheasymmetriccarbonatomsofmonosaccharides,theprefixesDandLareusedtogetherwithprefixesderivedfromthetrivialsugarnames(e.g.,D-glycero-,L-arabino-,D-xylo-)followedbypentose,hexosehexulose,etc.Asopen-chainhydroxyaldehydesandhydroxylketenes,themonosaccharidesareveryreactive.TheyreadlyenolizeinalkalinesoluionstoreduceionssuchasCu2+andFe(CN)63-.Therefore,theyarecalled“reducingsugars”.Plantsprotectthereactivemonosaccharidesfortransportandstoragebycondensingthemwithlossofwater,intolessreactivesugars,e.g.,D-glucoseandD-fructose,arecondensinginsuchawaythattheirreactivefunctionsarelosttoformthedisaccharidenoreducingsugar,sucrose.Thelessreactivesucroseisthentransportedtoallpartsoftheplantforenzyminsynthesesofoligo-andpolysaccharides.FromthousandsormoreD-glucosemoietiesofsucrosetheglucans,starchandcellulose,arebuilt.FromtheD-fructosemoietyofsucrose,fructanssuchasinulinareassembled.Otherpolysaccharidesareformedfromothersugar,whichrosebyenzymictransformationsofphosphorylatedhexoesandsugarnucleotides.Theprefix“glyc,”isusedinagenericsensetodesignatesugarsandtheirderivatives;e.g.,glycoses,glycosides,glycosans,glyconicglyceric,andglycuronicacids.Thegenericnameforpolysaccharidesis“glycan”homoglycansarecomposedofsinglemonosaccharide;forexample,theD-glucans,celluloseandstarch,releaseonlyD-glucosebyhydrolysis.Otherhomoglycans(e.g.,thehexcsans,D-galactanandD-manan,andthepentosans,L-arabinanandD-xy-lan)areuncommoninnature.Heteroglycans,composedoftwoormoredifferentmonosaccharides,arewidelydistributedthanthehomoglycansthatarenotglucans.Galactomnnans,glucomammans,arabinogalactans,andarabinoxylansarecommondiheteroglycans(composedoftwosugars).theglycantvailoverfreeglycosesinnaturalfoods.Tdoxidationofaldosesyieldsaldonicacids,HOCH2-(CHOH)n-COOH;e.g.,gluconicacid(n=4).oxidationofbothendsofthealdosemoleculeyieldsaldaricacids,HOOC-(CHOH)n-COOH;e.g.,tartaricacid(n=2).OxidationoftheterminalCH2OHgroupofhexoseswithoutoxidationofthereducingfunction(protected)produceshexuronicacids,HOOC-(CHOH)-CHO.Thehexuronicacidsarecommonmonosaccharideconstituentsofmanyheteroglycans.forexample,theyarefoundinacidichemicelluloses,pecticsubstances,alginplandexudategumes,andthemucopolysaccharidesofmammaliantissues.Penturonicacidshavenotbeenfoundinnature.Reductionofaldosesorketosesyieldsugaralcohols,properlycalled‘a(chǎn)lditols,”HOCH2-(CHOH)n-CH2OH.thesuffix“-itol“isappliedtothetrivialprefixestodenotedifferentalditols;e.g.,D-glucitol,D-manniitol,xylitol.Thetriitol,gllyceritol(bycommonusage,glycerol,n=1),isthealditolmoietyoffats.GlycerolandD-glucitol(sorbitol)areacceptableandusefulfoodaddiaffinityforwater.Pentitols(n=3)andhexutols(n=4)arefoundinsmallamountinmanyfruits,vegetablesandhexitol,perseitol(n=5),andanoctitolhavebeenisolatedfromavocados.Someaditolsarenutritionallyavailable;othersarenot.OthertypesofcarbohydratesfoundinfoodarethecondensedN-acetylatedaminosugarsofmucopolysaccharides,glycoproteins,andchitin;thecondensedeoxysugarsofgum,mucilages,andnucleotides;glcosides(sugarscondensedwithnonsugars);glucosinolates(toxicthioglycosides);cyclitols(myoinositol,phyticacid);andreductone,L-ascorbicacid.Complexcarbohydrates,suchascelluloseandhemicellulose,arelargelyindigestible,asareanumberoforigins

CarbohydrateCompositionofFoods

Detainsneedmoreexactinformationonthecarbohydratecompassionoffoods.Foodpressersalsomakepracticaluseofcarbohydratecompositiondata.Forexample,thereducingsugarcontentoffruitsandvegetablesthataretobedehydratedorprocessedwithheatisfrequentlyanindicatoroftheextentofnonenzymicbrowingthatcanexpectedduringprocessingandstorage.Thepossiblehydrolysisofsucrosetoreducingsugarsduringprocessingalsoistobeconsidered.thenaturalchangesincarbohydratecompositionthatoccurduringmaturationandpostharvestripeningofplantfoodsisthereforeofparticularinteresttofoodchemists.Citrusfruits,whichnormallyripenonthetreeandcontainnostarch,undergolittlechangeincarbohydratecompositionfollowingharvest.However,infruitthatarepickedbeforecompleteripening(e.g.,apples,bananas,pears),muchofthestoredstarchisconvertedtosugarsasripeningprocess.Thereducingsugarcontentofpotatoesalsoincreaseduringthesundryingofgrapesanddates,sucroseisconvertedtoD-glucoseandD-fructose;accordingly,thecolorofthedriedproductsisdeepenedbynonenzymicbrowningreactions.Greenpeas,greenbeans,andsweetcornarepickedbeforematuritytoobtainsucculenttexturesandsweetness.Laterthesugarswouldbeconvertedtopolysaccharides,waterwouldbelost,andtoughtextureswoulddevelop.Insoybean,whichisallowedtomaturecompletelybeforeharvest,thestarchreserveisdepletedassucroseandgalactosylsucroses(raffinose,stachyose,verbascose,etc.)areforminthemaltingofcerealgrains,rapidconversionsofreservecarbohydratetosugarsoccurasenzymesarestronglyactivated.Infoodsofanimalorigin,postmortemactivityofenzymesmustbeconsideredwhencarbohydratecompositiondataisobtained.Theglycogenofanimaltissues,especiallyliverisrapidlydepolymerizedtoD-glucoseafterslaughter,andimmediatedeepfreezingisrequiredtopreservetheglycogen.Mammalianinternalorgans,suchasliver,kidney,andbrainsalsoeggsandshellfish,providesmallamountofD-glucoseinthediet.Redfreshmeatscontainonlytracesofavailablecarbohydrate(D-glucose,D-fructose,andD-ribose)andtheseareextractedintobouillonsandbroths.Dairyproductsprovidethemainsourceofmammaliancarbohydrate.Wholecow’smilkcontainsabout4.9%carbohydratesanddriedskimmilkcontainsover50%lactose.Examinationoffoodcompositiontablesshowsthatingeneral,cerealsarehighestinstarchcontentandlowestinsugars.Fruitarehighestinfreesugarsandlowestinstarch.onadrybasis,theedibleportionsoffruitusuallycontain80-90%carbohydrate.Legumesoccupyintermediateportionwithregardtostarchandarehighinunavailablecarbohydrate.Glycosidesofmanytypesarewidelydistributedinplants.Certainbiologicallyactivethioglucosides,properlycalled“glucosinolates”,arefoundinsignificantamountincrucifers.Mustardoils,nitriles,andgoitrinsarereleasedbyenzymichydrolysis.Theirsuspectedgoitrogenicinhumanshavebeeninvestigated,buttheamountofglucosnolatesnormallyconsumedinfoodsuchasfreshcabbage(300-1000ppm),cauliflower,Brusselssprouts,turning,rutabagas,andradishesarenotnowbelievedtocauseadversephysiologicaleffects.Cyangeneticglycosides,whichreleasehydrogencyanidebyenzymichydrolysisundercertainconditionofvegetablemaceration,areknowntobesourcesofacutetoxicityincertainanimalfeeds;howevertheyarenotactiveinthecustomaryfoodsofdevelopedcountries.Certainforeignvarietiesoflimabeansandmanicroot(cassava)mayyieldupto0.3%hydrogencyanidebyweight,butlimabeansdistributedintheUnitedStatesyieldlessthan0.02%.Saponins,thesurface-activeglycosidesofsteroidsandtriterpenoids,arefoundinlowconcentrationsintealeaves,spinach,asparagus,beetssugarbeet(0.3%),yams,soybeans(0.5%),alfalfa(2-3%),andpeanutsandotherlegumes.LESSON3LIPIDSANDTHEIRUSESINFOODSThechemistryoffoodlipidsiscomplicatedbecausetheyarediversetypesofcompoundsthatundergomanyinteractionswithothercomponentsofafood.Manyimportantandwell-understoodchemicalchangesthatoccurinanisolatedlipidmaybemodifiedbysuchfactorsaslocationofthelipidinatissuesystem,thepresenceorabsenceofwater,andtheimpositionofsuchstressesasheatorradiation.Metals,bothinthefreestateasironsandascomponentsoforganmetalliccompounds,affectthechemistryoflipids,especiallyinoxidationreactions.Non-lipidcomponentsofafoodmayinteractwithlipidsandthiscanproducechangeinfoodquality.

DEFINITIONANDCLASSIFICATIONOFLIPIDS

Theconsumerandtheprocessoroffoodsutilizesubstancesfromthenutrientsgroupknownasfatsandoils.Fatsandoilsrepresentthemostprevalentsinglecategoryofaseriesofcompoundsknownaslipids.Theword"lipid"isdefinedinWebster’sunabridgeddictionaryas“anyofagroupsubstancethatsparinglysolubleinether,chloroform,orothersolventsforfatsbutareonlysparinglysolubleinwater,thatwithproteinsandcarbohydratesconstitutetheandprincipalstructuralcomponentsoflivingcells,andrelatedandderivedcompounds,andsometimessteroidsandcarotenoids,"Thisdefinitiondescribesabroadgroupofsubstancesthathavesomepropertiesincommonandhavesomecompositionalsimilarities.AclassificationoflipidsproposedbyBloorcontainsthefollowingelements,whichareusefulindistinguishingthemanylipidsubstances:1.Simplelipids(neutrallipids)-estersoffattyacidswithalcohols.a.Fats:estersoffattyacidswithglycerol.b.Waxes;estersoffattyacidswithalcoholsotherthanglycerol.2.Compoundlipids-compoundscontainingothergroupsinadditionesterofafattyacidwithanalcohol.a.Phospholipids(phosphatides):esterscontainingfattyacids,phosphoricacidandothergroupsusuallycontainingnitrogen.b.Cerebrosides(phosphatides);compoundscontainingfattyacids,acarbohydrateandanitrogenmoiety,butnophosphoricacidc.Othercompoundlipids:sphingolipids:sphingolipidsandsulfolipids3.Derivedlipids-substancesderivedfromneutrallipidsorcompoundlipidsandhavinggeneralpropertiesoflipids.a.Fattyacidsb.Alcohols:usuallynormalchainhigheralcoholsandsterolsc.HydrocarbonsFoodsmaycontainanyorallofthesesubstancesbutthoseofgreatestconcernarethefatsorglycosidesandthephosphatides.Theterm“fatis”applicabletoalltriglyceridesregardlessofwhethertheyarenormallynonliquidorliquidatambienttemperatures.Liquidfatsarecommonlyreferredtoasoils.Suchoilsassoybeanoil,cottonseedoil,andoliveoilareofplantorigin,lardandtallowareexamplesofnonliquidfatsfromanimals,yetfatfromthehorseisliquidatambienttemperaturesandisreferredtoashorseoil.Fatsandoilsalsocanbeclassedaccordingto“groupcharacteristics.”Fivewell-recognizedgroupsarethemilkfatgroup,thelauricacidgroup,theoleiclinoleicacidgroup,thelinolenicacidgroup,andtheanimaldepot-fatsgroup.Themilkfatgrouppertainsessentiallytothemilkofruminantsandespeciallytothatofthecow,althoughincertainareasmilkofthewaterbuffaloofsheepandgoatsmaybeprominent.,Milkfatsarecharacterizedby30-40%oleic,25-32%palmitic,and10-15%stearicacids.Theygenerallyhavesubstantialamountsofc4-c12acidsandaretheonlycommonlyusedfatstocontainbutyricacid,whichcompositionisparticularlysusceptibletovariationasaconsequenceoftheanimal’sdiet.Thelauricacidgroupischaracterizedbyahighproportion(40-50%)oflauricacid(c12)andlesseramountsofc8,c10,c14,c16,andc18acids.theunsaturatedacidcontentisverylowandthiscontributestoextremelygoodshelflife.Thesefatsgenerallymeltatlowtemperaturesbecauseoftheshortcarbonchainspresent.Themostwidelyusedfatsofthisgrouparefromthecoconut,seedsoftheoilpalm,andthebabassuorthecoquillanut.Theoleic-linole9ocacidgroup,thelargestandmostvariedgroup,containsonlyfatsand