食品分析實(shí)驗(yàn)報(bào)告 DNS

Date:2011-05-22

Experimentaltitle:Determinationofreducingsugarcontent—DNSmethod

Principle:Determinationofreducingsugaristhebasicmethodforthedeterminationofsugarcontent.Reducingsugarisfreealdehydeorketonecontainingsugar.Monosaccharidesarereducingsugars,disaccharidesandpolysaccharidesarenotnecessarilyreducingsugar.Lactoseandmaltosearereducingsugars,sucroseandstarchnon-reducingsugar.Thesolubilityofthedifferentuseofsugar,youcansamplemonosaccharide,disaccharides,andpolysaccharideswereextracted.(Notreducing)disaccharidesandpolysaccharidescanbedouble-acidhydrolysismethod.Outingtodoublesugarandreducingthedegradationintoasinglesugardetermination.Inthesamplewerecalculatedreducingsugarscontent.Contentofreducingsugarwithglucoseinstead.

Procedures:

Reagentpreparation:

DNSReagentconfiguration

InNaOHsolution,byaddingdinitrosalicylicacidsolutionandpotassiumsodiumtitrate

NaOHsolutionbyaddingcrystallinephenol,addwatertodissolve,andfinallysetthevolume.

Take(2)69mLanhydroussodiumsulfite6.9g,todissolve

To(3)into(1),thecompletelydissolved,storedinbrownreagentbottle.Atroomtemperature,place7-10dayslatertouse

Glucosestandardsolutionconfiguration

Accuratelyweigh100mgofanalyticalgradeglucose(pre-driedat105℃toconstantweight),dissolvedindistilledwaterwithasmallamountofvolumeto100mL,refrigeratoruse.

Operationmethods

Takesixcleantesttubes,addingvariousreagentsinthefollowingorder

Glucosesolution

Distilledwater

DNSreagent

0

1

2

3

4

5

Theamountofsugarcontained(mg)

0

0.2

0.4

0.6

0.8

1.0

Distilledwater(ml)

1

0.8

0.6

0.4

0.2

0

DNSreagent

3ml

Distilledwater(ml)

2.5ml

Heating

Heat5minutes(90°C)

Cooling

Immediatelywiththeflowofcoldwatertocool

Opticaldensity

(OD)

0.76

1.086

1.522

2.053

2.783

3.342

Results:

Mixtheabovesolution,eachtubeafterthephotoelectriccolorimeter(510nm)forcolorimetricdeterminationoftheblankcontrolsolutionwithzeroadjustment,recordingtheopticaldensityvalue.Glucoseconcentrationastheabscissa,theordinateisopticaldensitystandardcurveplotted.

Discussion:

Inalkalinesolution,thereducingsugarintoeneglycol(1,2-eneglycol).

Eneglycolofvariousoxidantssuchasironcyanideeasily,3,5-dinitrosalicylicacidandCu2+oxidizedtosugaracids.Cyanideanddynatron-salicylicacidsaltreductionisthebasisforquantitativedeterminationofreducingsugar.Dinitrosalicylicacidreducingsugarandalkalinereagentisheatedtogethertoproduceabrown-redaminocompounds,atacertainconcentrationrange,thedepthofthecolorbrownmaterialdegreeproportionaltotheamountofreducingsugar.Therefore,wecandeterminethesampleamountofreducingsugarandtotalsugar.

WhenyouconfigureDNSreagent,tonote3,5-dinitrosalicylicacidandNaOH,addingtimemustbeveryclose,ortojointheNaOH.Orwillcausetheprecipitationofinsoluble,leadingtothepreparationofthesolutiontofail.Andtheconfigurationprocess,thesolutionheatingtemperatureshouldnotexceed50degreesCelsius.

WhenyouconfigureDNStoaddpotassiumsodiumtitratesolutionwastoremovetheinsideofthedissolvedoxygen,dissolvedoxygenandmoreso,shortentheshelflifeofasampleatdifferenttimes,theresultsofthedeterminationoflargedifferences(sugardissolvedoxygenseriousinterferencecolor).Anhydroussodiumsulfiteisstablecolor,andphenolwiththecolorofthecolorismorestable

Conclusion:

Inthe3,5-dinitrosalicylicacidreducingsugarincolorimeters,NDSisthemainreagent.Itisredandbrownsugarreactionmaterial.ButthecolorjustthewordswiththeDNS,notalinearrelationshipbetweencolorandconcentration.Orlinearpoor.AddtheaimofincreasingDNSphenolcolorreagentforquantitativedeterminationofthelinearrelationshipbetweenreducingsugarconcentration.Thepresenceofphenolisessential.NDSdoesnotparticipateinthecolorofphenolnotquantitative.However,duetotheaireasilyoxidizedphenolcase,theremainingphenolinordertoensurethatallstepsarenotoxidized.Addingasufficientamountofpotassiumsodiumtartrateistoeliminatetheimpactofdissolvedoxygen,sodiumsulfitecanbeaddedtofurtherenhancethestabilityofreagents.

DNSstandardcurvepreparation,setaconcentrationgradientwhenthecontentshouldbezeroDNSreagentasreferenceinsteadofusingDNSasareference.

Standardcurveshouldbewithintheconcentrationrangeinalinearrelationship.BestR=0.999ormore.Thisofcoursedoesnotruleoutthepossibilityofalargeconcentrationrange.DNSandtheroleofthelinearrelationshipbetweenreducingsugarandtheamountofreagenthavenothingtodo.3,5-dinitrosalicylicacids