食品科学专业英语阅读练习

LESSON1NUTRITION

Whatweeataswellashowmuchweeatdetermineournutritionstatustoanimportantextent,

andinfluencedbyadiversityofexternalandinternalfactors.

Thepersonwhowantstofinetheanswertothequestion"whatshouldIeatforgood

nutrition?”,mighteasilybecomelostinthemazeofinformationalcorridors,confusedbythe

wealthoftechnicalinformationprovidedbyscientistsormisleadbysimplisticanswersprovided

bythosewithproductstosell.Somewhereinbetweenissomereasonable,commonsense

informationthatwecanusetoguideusourquestforsoundnutritionknowledgeo

Tobegin,weneedtolearnsomedefinitionsofcommonlyusednutritiontermsandfindout

whatsortsofguidelinesareavailabletohelpusmeasurethequalityofourdietsandtodevelop

healthfuleatingpatterns.

NUTRITIONANDFOOD:DEFINITIONS

Thewordnutritionisoftenpairedwiththewordfoodbecausethetwogotogether.Theyare

interdependent,butnotinterchangeable.

Foodmightbedefinedasanyediblesubstancethatprovidesnourishmentwhenconsumed.Itis

madeupofmanynaturalingredientsallchemicalsthathavedifferentfunctionssuchasproviding

odor,flavor,color,andnourishment.Theingredientsthatgiveusnourishmentarecallednutrients.

Thesenutrientsarecategorizedasfats,proteinscarbohydrates(sugarsandstarches),minerals,

vitamins,andwater.Theyarecalledessentialnutrientsbecausewecannotgetalongwithoutthem.

Weneedthemforenergy,forbuildingandmaintainingbodytissue;andforregulatingbody

processesthethreeessentialfunctionsoffoodsinthebody.

Nutritionmightbedefinedastheprocesswherebyweobtaintheessentialnutrientsandusethem

tomakemanyothersubstancesourbodiesneed,thisprocesswouldincludeeatinganddigesting

foodandabsorbingandusing,ormetabolizing,thenutrientsitcontains.

Wecanobtainalloftheessentialnutrientsfromfood.However,itispossibletoobtain

nourishmentwithouteatinganddigestingfbod-if,forexample,thenutrientsareinjecteddirectly

toourveinsasinintravenousfeeding.

Thus,itisthenutrientsthatareessentialandthefoodthatnormallyprovidesthem.Since

foodisvital,weneedtoknowthenutritivecontentoffoods,whichonesarethebestsourcesof

thevariousnutrientsandhowtocombinethemintoahealthfuldiet.

Thetermgoodnutritionimpliesthatweareobtainingfromourfoodalloftheessential

nutrientsintheamountsneededtokeepourbodiesfunctioningandtomaintainoptimumhealth.A

verysimplifieddefinitionofgoodnutritionmightbe"eatingtherightfoodsintherightamounts.”

Theworkofnutritionscientistsinvolvesfindinginthebody,theamountofeachthatweneed,

whathappeningswhenwereceivetoomuchortoolittleandaboutfoodanddied-whatfoodswe

shouldeatandinwhatamount.

Yetnutritionscienceinitsbroadestsensehasmanymorefacets:theinfluenceofsensory

factorsofflavor,color,andtextureoffoodoneatingbehavior;thepsychological,cultural,

emotional,andsocialaspectsoffoodintake;andeventheeconomicsoffoodavailabilityand

consumerbehaviorinthepurchaseoffood

THENUTRIENTS

Todate,nutritionscientistshaveidentifiedsome40to45substancesasessentialnutrients.

Butthelistisgrowingasnewnutrientscontinuetobeidentified;thehistoryofnutritionscience

containsfascinatingstoriesaboutthewaysfoodsubstanceshavebeenidentifiedasessential

nutrients.Insomeinstances,medicalresearchersseekingthecauseofaparticulardiseasefound

thatproblemwasduetoasinglesubstance,andthatwhenthissubstancewasaddedtothediet,the

symptomsofthediseasedisappeared.Anumberofvitaminswerediscoveredinthisway.

Nutrientsmightbedividedintotwogenialcategoriesbasedontheamountthatweneed.

Thesearethemacronutrients(carbohydrates,fats,proteins,andwater),whichweneedin

relativelylargeamountsandthemicronutrients)mineralelementsandvitamins),whichweneed

inrelativelysmallamounts.Allofthenutrientsexceptformineralelementsandwaterare

classifiedasorganicchemicalsbecausetheycontaintheelementcarbon.Mineralelementsand

waterareinorganicchemicalsbecausetheydonotcontaincarbon.

Thevitaminsaredividedintotwogeneralcategorizesbasedontheirsolubilityineitherwater

orfat.thefat-solublevitaminsarevitaminsA,D,E,andK;thewater-solublevitaminsinclude

vitaminsC(ascorbicacid),niacin,thiamin,riboflavin,flacon(alsocalledfolicacid)antitheticacid,

pyridoxine,vitaminB12andbiotin.

Themineralelementsaredividedintotwocategoriesbasedonthequantityofthemthatwe

need.Microelementsarethoseneededinrelativelylargeamounts,whilemicroelementsarethose

neededinverysmallamounts,someexampleofmicroelementsaresodium,calcium,and

phosphorus.Someexampleofmicroelementsisiron,iodine,manganese,zinc,andfluorine.

RECOMMENDEDDIETARYALLOWANCES

Onceanutrientisidentified,oneoftheprincipalresearcheffortsofnutritionscientististo

determinehowmuchofitisneededbypeopleatvariousagesandstagesoflife.Initialstudies

usuallyareconductedwithlaboratoryanimals,buttheinformationdevelopedinthesestudies

cannotbeapplieddirectlytohumanssincepeople*sneedsoftenarequitedifferentfromanimals'

needs.Humannutritionstudiesontheotherhand,aretime-consuming,costly,anddifficultto

conduct,especiallybecauseoftheproblemsofcontrollingvariablesandpossiblycausingharmto

theindividualsinvolved.Becauseoftheobstaclestocollecting,accuratedata,ourpresent

knowledgeofnutrientneedsisincomplete,andtherequirementsofhumansformanynutrients

havenotbeenestablished.

However,thedataonhumanandanimalneedscurrentlyavailableareusedbynutrition

scientiststoestablishestimatesoftheamountsofessentialnutrientsperdaythatwillmeetthe

needsofmosthealthpersons.IntheUnitedStates,themostwidelyusednutrientguidelinesare

therecommendeddietaryallowance(RDA),whichareissuedbythenationalacademyofsciences,

nationalresearchcouncil,andfoodandnutritionboard.

TheRDAservesasdietaryofnutritionalstandardsforawiderangeofage-weight-sex

groupssuchasinfants,children,adolescents,pregnantandlactatingwomen,andyoungerand

olderadults.Theyarerecommendations,notaveragerequirements,forsatisfactorylevelsofintake

ofessentialnutrientsofpopulationgroupsofaverage,healthypeople.Theydonottakeaccountof

specialneedscertainindividualsmayhaveduetogeneticmakeup,metabolicdisorders,chronic

infections,andotherabnormalities,whichmayresultintheirneedingdifferentlevelsofnutrients.

MARGINofSAFETYALLOWSforINDIVIDUALDIFFERENCES

Toallowforindividualdifference,theusuallyaresetwithagenerousmarginofsafety.Thus,

theyarethoughttomeettheneedsof95to97percentofthepeoplewithineachage-sexgroup.In

otherwords,theRDAexceedtherequirementsofmostindividualstoensurethattheneedsof

nearlyallaremeet.Forthisreason,apersonwhoconsumesadietthatprovideslessthantheRDA

foroneormoreessentialnutrientsisnotnecessarilygettingadietthatisnutritionallyinadequate.

Whatcanbeconcluded,however,isthatthefarthertheintakeofanessentialnutrientfallsbelow

theRDA,thegreatertheprobabilityofnutritionalinadequacy,ontheotherhand,ifanindividual

isgettingalltheessentialnutrientsatorabovetheRDAlevelofhisorherage,chancesaregood

thatdietisnationallyadequate.

AnexceptionistheRDAfbrenergyorcalories,whicharenotdesigned,asguidesfbr

individualcaloricneeds.OthervariablesnotincludedintheRDA,suchasbodysizeandphysical

activity,areinvolvedinanindividualJscaloricrequirements

DIFFERENCESINNUTRIENTUTILIZATIONCONSIDERED

AnotherfactorconsideredwhentheRDAareestablishedistheavailabilityofthenutrient

andfactorsthataffecthowefficientlyitisusedinthebodyforsomenutrients,suchasiron,

absorptionoruseinthebodymaybeincomplete;sotheRDAneedstobesethighenoughtoallow

forthis.Andbecauseinthecaseofcertainothernutrients,substancefoundincarrotsandother

vegetablesandfruits,whichourbodiesconverttovitaminA.

Ontheothersideofthecoin,receivingtoomuchofcertainnutrients,amounts

significantlyabovetheRDA,canbejustharmfulasnotobtainingenoughcertain

vitamins(suchasAandD)andmineralscanbehighlytoxicifhighforoptimal

nutrientintakefromthestandpointofbothmaximumandminimumlevels.

LESSON2CARBOHYDRATES

Thefoodscientisthasamany-sidedinterestincarbohydrates.Heisconcernedwiththeir

amountsinvariousfoods,availability(nutritionalandeconomic),methodsofextractionand

analysis,commercialformsandpurity,nutritionalvalve,physiologicaleffects,andfunctional

propertiesinfoods.Understandingtheirfunctionalpropertiesinprocessedfoodsrequiresnotonly

knowledgeofthephysicalandchemicalpropertiesofisolatedcarbohydrates,butalsoknowledge

ofthereactionsandinteractionsthatoccurinsitusbetweencarbohydratesandotherfood

constituentsandtheeffectsofthesechangesuponfoodqualityandacceptance.Thisisatallorder

forknowledge.Becauseprocessingaffectsbothnutritionalandestheticvaluesoffood,knowledge

ofthechangesthatcarbohydratesundergoduringmilling,cooking,dehydration,freezing,and

storageisespeciallyimportant.

Studentsareadvisedtostudythefundamentalchemistryunderlyingusefulcarbohydrates

propertiesOfservicewillbeanunderstandingoftheassociationofpolarmoleculesthrough

hydrogenbonding,ioniceffects,substituenteffects,chelationwithinorganicions,complexing

withlipidsandproteins,anddecompositionreaction.Thisbackgroundwillprovidean

understandingofpropertiesthataffectthetextureandacceptanceofprocessedfoods(e.g.,

solubility,hygroscopicity,diffusion,osmosis,viscosity,plastity,andflavorproduction),properties

thatenabletheformationorhighqualitypastries,gels,coatings,confections,andreconstitutable

dehydratedandfrozenfoods.

Abilitytopredictwhatchangesinfunctionalpropertiesarelikelytoensuefrom

incorporatingvarioustypesofcarbohydratesintoprocessedfoodsisapracticalgoalofthefood

scientist.Suchforecastingrequireseitherawealthofexperiencewithtrial-and-errormethodsora

deepknowledgeofcarbohydratepropertiesasrelatedtostructure-perhapsboth.However,

scientificknowledgeofcauseandeffectishighlyrespectedwhenitshortensindustrial

developmenttime

Source,Types,andTerminology

Thelayman'sconceptionofcarbohydratesgenerallyinvolvesonlythesugarsandstarchesof

foods一thosethatgeneratecaloriesandfat.Thefoodchemistknowsmanyothertypesthatare

ingested.

Becausemostpeopleenjoythesweetnessofsugarsandthemouthfeelofcookedstarches,

theybecomefamiliarbyassociationwithtablesugar(sucrose),invertsugar'shydrolyzedsucrose,

cornsyrupsugars(D-glucoseandmaltose),milksugar(lactose),andthemorestarchyfoods.

Thesecarbohydratesarenutritionallyavailable;ie,theyaredigested(hydrolyzedtocomponent

monosaccharides)andutilizedbythehumanbody。Carbohydratesofdietaryfiber(cellulose,

hemicelluse,pentosans,andpecticsubstances),incontrast,tendtobeoverlookedbecausethey

arelargelyunavailable.Digestiveenzymesdonothydrolyzethemsignificantly;nevertheless,they

maybequiteimportantforhumanhealth.

Thecarbohydratesofnaturalandprocessedfoodsaredividedintoavailableand

unavailabletypes.Theavailablecarbohydratesvaryindegreesofabsorptionandutilization

dependinguponquantitiesingested,accompanyingfoodtypes,andhumandifferencesin

complementsofdefectiveenzymesandintestinaltransportmechanisms.Malabsorption

difficultiesandadversephysiologicaleffectsareknownforalltheavailablecarbohydratesbut

gelatinizedstarchesgivelittleornotrouble.

Itisimportanttorealizethatinruminantstheunavailableandmostabundant

polysaccharidecelluloseispartiallyhydrolyzedtothesamehighlyavailablesugarthatstarch

providesupondigestion;i.e.D-glucose.Grazinganimalsdoitthroughthecellulosesgeneratedby

themicroorganismsoftheirrumen.Celluloseis,therefore,acontributingsourceofvolubleanimal

protein.Foodchemistsprobablycanimproveupontheefficiencyandeconomicsoftheruminant'

sconversionofcellulosetonutrients.Developmentofcellulosesthatarestableoutsidethecellsof

microorganismsenablestheculturingoffungiandwithyeastsoncellulosehydrolyzates.Fungi

(e.g.,mushrooms)canproduceproteinwiththebiologicalvalueofanimalprotein.Theconversion

ofcellulosewastestoanimalfeedandhumanfoodisanintriguingprospectforlimiting

environmentalpollutionandforfeedingtheworld'expendingpopulation.

Carbohydrateswerefirstnamedaccordingtotheirnaturalsources;e.g.,beetsugar,cane

sugar,grapesugar,maltsugar,milksugar,cornstarch,liverglycogen,andsweetcornglycogen.

Trivialnameswerethenformed,inEnglishterminology,oftenfromaprefixrelatedtothesource

followedbythesuffix"-ose”todenotecarbohydrate.Namesarisinginthisway,forexample,are

fructose,maltose,lactose,xylose,andcellulose.Theseshort,well-establishednamesarestill

commonlyused.Theyfurnishnoinformationonthechemicalstructureshowever,soadefinitive

carbohydratenomenclaturehasbeendeveloped.Fromthedefinitivenames,structuralformulas

canbewritten.Someofthetermsinvolvedinthedefinitivenomenclatureareexplainedinthe

followingparagraphs.

Thesimplesugars(monosaccharidesOarebasicallyaliphaticpolyhydroxyaldehydesand

ketones:HOCH2-(CHOH)n-CHOandH0CH2-(CHOOH)n-1-C-O-Ch2OH,called“aldoses”

and“ketoses,“respectively.However,itmustbeunderstoodthatcyclichemiacetalsofthose

open-chainformsprevailIsolidsandatequilibriuminsolutions.Inthedefinitivenomenclature,

thesuffix"ose"isappendedtoprefixesdenotingthenumberofcarbonatomsinthe

nomosaccaride;e.g.trioses(n=l),tetroses(n=2),pentoses(n=3),hexoses(n=4)todistinguish

aldosesfromketoses,ketosesaredesignatedas”-uloses.wThus,thesimplestketose,

HOCH2-C:O-CH2OH,isatriulose;themostcommonketose,D-fructose(levulose),isahexlose.

Todesignatetheconfigurationsofhydroxylgroupsontheasymmetriccarbonatomsof

monosaccharides,theprefixesDandLareusedtogetherwithprefixesderivedfromthetrivial

sugarnames(e.g.,D-glycero-,L-arabino-,D-xylo-)followedbypentose,hexosehexulose,etc.

Asopen-chainhydroxyaldehydesandhydroxylketenes,themonosaccharidesarevery

reactive.TheyreadlyenolizeinalkalinesoluionstoreduceionssuchasCu2+andFe(CN)63".

Therefore,theyarecalledureducingsugars”.Plantsprotectthereactivemonosaccharidesfor

transportandstoragebycondensingthemwithlossofwater,intolessreactivesugars,e.g.,

D-glucoseandD-fructose,arecondensinginsuchawaythattheirreactivefunctionsarelostto

formthedisaccharidenoreducingsugar,sucrose.Thelessreactivesucroseisthentransportedto

allpartsoftheplantforenzyminsynthesesofoligo-andpolysaccharides.Fromthousandsormore

D-glucosemoietiesofsucrosetheglucans,starchandcellulose,arebuilt.FromtheD-fructose

moietyofsucrose,fructanssuchasinulinareassembled.Otherpolysaccharidesareformedfrom

othersugar,whichrosebyenzymictransformationsofphosphorylatedhexoesandsugar

nucleotides.

Theprefix"glyc,“isusedinagenericsensetodesignatesugarsandtheirderivatives;e.g.,

glycoses,glycosides,glycosans,glyconicglyceric,andglycuronicacids.Thegenericnamefor

polysaccharidesis“glycan“homoglycansarecomposedofsinglemonosaccharide;forexample,

theD-glucans,celluloseandstarch,releaseonlyD-glucosebyhydrolysis.Otherhomoglycans

(e.g.,thehexcsans,D-galactanandD-manan,andthepentosans,L-arabinanandD-xy-lan)are

uncommoninnature.Heteroglycans,composedoftwoormoredifferentmonosaccharides,are

widelydistributedthanthehomoglycansthatarenotglucans.Galactomnnans,glucomammans,

arabinogalactans,andarabinoxylansarecommondiheteroglycans(composedoftwosugars).the

glycantvailoverfreeglycosesinnaturalfoods.

Thereducingsugarsarereadilyoxidized,mildoxidationofaldosesyieldsaldonicacids,

HOCH2-(CHOH)n-COOH;e.g.,gluconicacid(n=4).oxidationofbothendsofthealdosemolecule

yieldsaldaricacids,HOOC-(CHOH)n-COOH;e.g,,tartaricacid(n=2).Oxidationoftheterminal

CH2OHgroupofhexoseswithoutoxidationofthereducingfunction(protected)produces

hexuronicacids,HOOC-(CHOH)-CHO.Thehexuronicacidsarecommonmonosaccharide

constituentsofmanyheteroglycans.forexample,theyarefoundinacidichemicelluloses,pectic

substances,alginplandexudategumes,andthemucopolysaccharidesofmammaliantissues.

Penluronicacidshavenotbeenfoundinnature.

Reductionofaldosesorketosesyieldsugaralcohols,properlycalled'alditols,“

HOCH2-(CHOH)n-CH2OH.thesuffix”-itol“isappliedtothetrivialprefixestodenote

differentalditols;e.g.,D-glucitol,D-manniitol,xylitol.Thetriitol,gllyceritol(bycommonusage,

glycerol,n=l),isthealditolmoietyoffats.GlycerolandD-glucitol(sorbitol)areacceptableand

usefulfoodaddiaffinityforwater.Pentitols(n=3)andhexutols(n=4)arefoundinsmallamountin

manyfruits,vegetablesandhexitohperseitol(n=5),andanoctitolhavebeenisolatedfrom

avocados.Someaditolsarenutritionallyavailable;othersarenot.

OthertypesofcarbohydratesfoundinfbodarethecondensedN-acetylatedaminosugarsof

mucopolysaccharides,glycoproteins,andchitin;thecondensedeoxysugarsofgum,mucilages,

andnucleotides;glcosides(sugarscondensedwithnonsugars);glucosinolates(toxic

thioglycosides);cyclitols(myoinositol,phyticacid);andreductone,L-ascorbicacid.Complex

carbohydrates,suchascelluloseandhemicellulose,arelargelyindigestible,asareanumberof

origins

CarbohydrateCompositionofFoods

Detainsneedmoreexactinformationonthecarbohydratecompassionoffoods.Food

pressersalsomakepracticaluseofcarbohydratecompositiondata.Forexample,thereducing

sugarcontentoffruitsandvegetablesthataretobedehydratedorprocessedwithheatis

frequentlyanindicatoroftheextentofnonenzymicbrowingthatcanexpectedduringprocessing

andstorage.Thepossiblehydrolysisofsucrosetoreducingsugarsduringprocessingalsoistobe

considered.thenaturalchangesincarbohydratecompositionthatoccurduringmaturationandpost

harvestripeningofplantfoodsisthereforeofparticularinteresttofoodchemists.

Citrusfruits,whichnormallyripenonthetreeandcontainnostarch,undergolittlechange

incarbohydratecompositionfollowingharvest.However,infruitthatarepickedbeforecomplete

ripening(e.g.,apples,bananas,pears),muchofthestoredstarchisconvertedtosugarsasripening

process.Thereducingsugarcontentofpotatoesalsoincreaseduringthesundryingofgrapesand

dates,sucroseisconvertedtoD-glucoseandD-fructose;accordingly,thecolorofthedried

productsisdeepenedbynonenzymicbrowningreactions.

Greenpeas,greenbeans,andsweetcomarepickedbeforematuritytoobtainsucculent

texturesandsweetness.Laterthesugarswouldbeconvertedtopolysaccharides,waterwouldbe

lost,andtoughtextureswoulddevelop.Insoybean,whichisallowedtomaturecompletelybefore

harvest,thestarchreserveisdepletedassucroseandgalactosyIsucroses(raffinose,stachyose,

verbascose,etc.)areforminthemaltingofcerealgrains,rapidconversionsofreserve

carbohydratetosugarsoccurasenzymesarestronglyactivated.

Infoodsofanimalorigin,postmortemactivityofenzymesmustbeconsideredwhen

carbohydratecompositiondataisobtained.Theglycogenofanimaltissues,especiallyliveris

rapidlydepolymerizedtoD-glucoseafterslaughter,andimmediatedeepfreezingisrequiredto

preservetheglycogen.Mammalianinternalorgans,suchasliver,kidney,andbrainsalsoeggsand

shellfish,providesmallamountofD-glucoseinthediet.Redfreshmeatscontainonlytracesof

availablecarbohydrate(D-glucose,D-fructose,andD-ribose)andtheseareextractedinto

bouillonsandbroths.Dairyproductsprovidethemainsourceofmammaliancarbohydrate.Whole

cow'smilkcontainsabout4.9%carbohydratesanddriedskimmilkcontainsover50%lactose.

Examinationoffoodcompositiontablesshowsthatingeneral,cerealsarehighestinstarch

contentandlowestinsugars.Fruitarehighestinfreesugarsandlowestinstarch.onadrybasis,

theedibleportionsoffruitusuallycontain80-90%carbohydrate.Legumesoccupyintermediate

portionwithregardtostarchandarehighinunavailablecarbohydrate.

Glycosidesofmanytypesarewidelydistributedinplants.Certainbiologicallyactive

thioglucosides,properlycalled“glucosinolates”,arefoundinsignificantamountincrucifers.

Mustardoils,nitriles,andgoitrinsarereleasedbyenzymichydrolysis.Theirsuspectedgoitrogenic

inhumanshavebeeninvestigated,buttheamountofglucosnolatesnormallyconsumedinfood

suchasfreshcabbage(300-1000ppm),cauliflower,Brusselssprouts,turning,rutabagas,and

radishesarenotnowbelievedtocauseadversephysiologicaleffects.Cyangeneticglycosides,

whichreleasehydrogencyanidebyenzymichydrolysisundercertainconditionofvegetable

maceration,areknowntobesourcesofacutetoxicityincertainanimalfeeds;howevertheyare

notactiveinthecustomaryfoodsofdevelopedcountries.Certainforeignvarietiesoflimabeans

andmanicroot(cassava)mayyieldupto0.3%hydrogencyanidebyweight,butlimabeans

distributedintheUnitedStatesyieldlessthan0.02%.Saponins,thesurface-activeglycosidesof

steroidsandtriterpenoids,arefoundinlowconcentrationsintealeaves,spinach,asparagus,beets

sugarbeet(0.3%),yams,soybeans(0.5%),alfalfa(2-3%),andpeanutsandotherlegumes.

LESSON3LIPIDSANDTHEIRUSESINFOODS

Thechemistryoffoodlipidsiscomplicatedbecausetheyarediversetypesofcompoundsthat

undergomanyinteractionswithothercomponentsofafood.Manyimportantandwell-understood

chemicalchangesthatoccurinanisolatedlipidmaybemodifiedbysuchfactorsaslocationofthe

lipidinatissuesystem,thepresenceorabsenceofwater,andtheimpositionofsuchstressesas

heatorradiation.Metals,bothinthefreestateasironsandascomponentsoforganmetallic

compounds,affectthechemistryoflipids,especiallyinoxidationreactions.Non-lipidcomponents

ofafoodmayinteractwithlipidsandthiscanproducechangeinfoodquality.

DEFINITIONANDCLASSIFICATIONOFLIPIDS

Theconsumerandtheprocessoroffoodsutilizesubstancesfromthenutrientsgroupknownas

fatsandoils.Fatsandoilsrepresentthemostprevalentsinglecategoryofaseriesofcompounds

knownaslipids.Theword"lipid1'isdefinedinWebster*sunabridgeddictionaryas“anyofa

groupsubstancethatsparinglysolubleinether,chloroform,orothersolventsforfatsbutareonly

sparinglysolubleinwater,thatwithproteinsandcarbohydratesconstitutetheandprincipal

structuralcomponentsoflivingcells,andrelatedandderivedcompounds,andsometimessteroids

andcarotenoids,“Thisdefinitiondescribesabroadgroupofsubstancesthathavesome

propertiesincommonandhavesomecompositionalsimilarities.

AclassificationoflipidsproposedbyBloorcontainsthefollowingelements,whichareuseful

indistinguishingthemanylipidsubstances:

1.Simplelipids(neutrallipids)-estersoffattyacidswithalcohols.

a.Fats:estersoffattyacidswithglycerol.

b.Waxes;estersoffattyacidswithalcoholsotherthanglycerol.

2.Compoundlipids-compoundscontainingothergroupsinadditionesterofafattyacidwithan

alcohol.

a.Phospholipids(phosphatides):esterscontainingfattyacids,phosphoricacidandother

groupsusuallycontainingnitrogen.

b.Cerebrosides(phosphatides);compoundscontainingfattyacids,acarbohydrateanda

nitrogenmoiety,butnophosphoricacid

c.Othercompoundlipids:sphingolipids:sphingolipidsandsulfolipids

3.Derivedlipids-substancesderivedfromneutrallipidsorcompoundlipidsandhaving

generalpropertiesoflipids.

a.Fattyacids

b.Alcohols:usuallynormalchainhigheralcoholsandsterols

c.Hydrocarbons

Foodsmaycontainanyorallofthesesubstancesbutthoseofgreatestconcernarethefatsor

glycosidesandthephosphatides.Theterm“fatis“applicabletoalltriglyceridesregardlessof

whethertheyarenormallynonliquidorliquidatambienttemperatures.Liquidfatsarecommonly

referredtoasoils.Suchoilsassoybeanoil,cottonseedoil,andoliveoilareofplantorigin,lard

andtallowareexamplesofnonliquidfatsfromanimals,yetfatfromthehorseisliquidatambient

temperaturesandisreferredtoashorseoil.

Fatsandoilsalsocanbeclassedaccordingto“groupcharacteristics.vFive

well-recognizedgroupsarethemilkfatgroup,thelauricacidgroup,theoleiclinoleicacidgroup,

thelinolenicacidgroup,andtheanimaldepot-fatsgroup.

Themilkfatgrouppertainsessentiallytothemilkofruminantsandespeciallytothatofthe

cow,althoughincertainareasmilkofthewaterbuffaloofsheepandgoatsmaybeprominent.,

Milkfatsarecharacterizedby30-40%oleic,25-32%palmitic,and10-15%stearicacids.They

generallyhavesubstantialamountsofc4-cl2acidsandaretheonlycommonlyusedfatsto

containbutyricacid,whichcompositionisparticularlysusceptibletovariationasaconsequence

oftheanimal'sdiet.

Thelauricacidgroupischaracterizedbyahighproportion(40-50%)oflauricacid(cl2)

andlesseramountsofc8,clO,cl4,c!6,andc!8acids,theunsaturatedacidcont