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1、Experimentthree・Determinationofproteincontentinfoods(Kjeldahlmethod)(5009.5-2003determinationofproteincontentinfoods)First,thepurposeandrequirements1.StudytheprincipleofKjeldahldeterminationofprotein.2.MastertheoperationtechniqueofKjeldahlmethod,ineludingdigestion,dist
2、illation,titrationandcalculationofproteincontent.Two、experimentalprincipleProteinisacompoundcontainingnitrogen.Foodwithconcentratedsulfuricacidandcatalystofcommonheatingdigestion,proteindecomposition,ammoniaandsulfuricacidproducedwiththegenerationofammoniumsulfateinthe
3、digestivefluid,thenaddalkalidistilledammoniafreeabsorbedwithboricacid,andhydrochloricacidstandardsolutiontitration,multipliedbytheproteinconversionfactoraccordingtotheconsumptionofacid,theproteincontent.Becausefoodscontainproteinsotherthannitrogen,theyarecalledcrudepro
4、teins・Three、instrumentsandreagents(I)reagent1,coppersulfate(CuS04・5H20)2,potassiumsulfate3,sulfuricacid(density1.8419g/L)4boricacidsolution(20g/L)5,sodiumhydroxidesolution(400g/L)6,0.Olmol/Lhydrochloricacidstandardtitrationsolution.7,mixedindicatorreagent:0.1%methylred
5、solution,1parts,and0.1%bromogreengreenethanolsolution5times,whenusedmixing・8,soybeanpowder・(two)instrumentMicronitrogendistillationunit:asshowninfigure3-.Fig.3-traceKjeldahlnitrogendevice1,electricfurnace;2,watervaporgenerator(2Lflatbottomedflask);3,spiralclampa;4,smal
6、lfunnelandrodglassstopper(sampleentrance);5,reactionchamber;6,reactionchamberouterlayer;7,rubbertubeandspiralclampB;8,condensertube;9,distillationliquidreceivingbottle・Four,experimentalsteps1.SampledigestionThesoybeanpowderisabout0.3g(+0.OOlg),intothedrylOOmLKjeldahlfl
7、ask,adding0.2g6Gcoppersulfateandpotassiumsulfate,slightlyshakebottleputasmallfunnel,adding20mLconcentratedsulfuricacid,thebottlewith450smallholesintheslantingangleasbestosline,usingelectricheatingdigestioninthehood,startwithlowheat,untiltheentirecontentsofcharring,foam
8、isstopped,thentoincreasethetemperaturetokeepboilinguntiltheliquid,digestedwithbluishgreenclearandtransparent,continue
