1、A Referencenumbe r ISO750:1998 (E) INTERNATIONAL STANDARD ISO 750 Secondedition 19980801 Fruitandvegetableproducts Determinationoftitratableacidity ProduitsdrivsdesfruitsetlgumesDterminationdelacidittitrableISO750:1998(E) ISO1998 Allrightsreserved.Unlessotherwisespecified,nopartofthispublicationmayb
2、ereproducedorutilizedinanyformorbyan ymeans,electronic ormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromthepublisher. InternationalOrganizationforStandardization Casepostale56 CH1211Genve20 Switzerland Internet isoiso.ch PrintedinSwitzerland ii Foreword ISO(theInternation
3、alOrganizationforStandardization)isaworldwidefederationofnationalstandardsbodies(ISO memberbodies).TheworkofpreparingInternationalStandardsisnormallycarriedoutthroughISOtechnical committees.Eachmemberbodyinterestedinasubjectforwhichatechnicalcommitteehasbeenestablishedhas therighttoberepresentedonth
4、atcommittee.Internationalorganizations,governmentalandnongovernmental,in liaisonwithISO,alsotakepartinthework.ISOcollaboratescloselywiththeInternationalElectrotechnical Commission(IEC)onallmattersofelectrotechnicalstandardization. DraftInternationalStandardsadoptedbythetechnicalcommitteesarecirculat
5、edtothememberbodiesforvoting. PublicationasanInternationalStandardrequiresapprovalbyatleast75%ofthememberbodiescastingavote. InternationalStandardISO 750waspreparedbyTechnicalCommiteeISO/TC 34, Agriculturalfoodproducts, SubcommitteeSC3, Fruitandvegetableproducts. Thissecondeditioncancelsandreplacest
6、hefirstedition(ISO750:1981),whichhasbeentechnicallyrevised.INTERNATIONALSTANDARD ISO ISO750:1998(E) 1 FruitandvegetableproductsDeterminationoftitratableacidity 1Scope ThisInternationalStandardspecifiestwomethodsforthedeterminationofthetitratableacidityoffruitandvegetable products: apotentiometricref
7、erencemethod; aroutinemethodusingacolouredindicator. Byconvention,thelattermethoddoesnotapplytowines. Inthecaseofsomecolouredproducts,itmaybedifficulttodeterminetheendpointofthetitrationinthelatter methodandtheformermethodshouldpreferablybeused. NOTEThedeterminationoftitratableacidityisofnovalueinth
8、ecaseofproductstowhichsulfurdioxidehasbeenadded. 2Principle 2.1Potentiometric method Potentiometrictitrationwithastandardvolumetricsolutionofsodiumhydroxide. 2.2Routine method Titrationwithastandardvolumetricsolutionofsodiumhydroxideinthepresenceofphenolphthaleinasindicator. 3Reagents Useonlyreagent
9、sofrecognizedanalyticalgrade,anddistilledordemineralizedwaterorwaterofequivalentpurity. 3.1 Sodiumhydroxide ,standardvolumetricsolution, c(NaOH)=0,1mol/l. 1) 3.2 Buffersolutions, ofknownpH. 3.3 Phenolphthalein,10g/lsolutionin95%( V/V)ethanol. 4Apparatus Usuallaboratoryapparatusand,inparticular,thefo
10、llowing. 4.1 Homogenizeror mortarandpestle . 4.2 Pipettes,todeliver25ml,50mlor100ml. 1)Previouslyexpressedas“0,1Nstandardvolumetricsolution.“ISO750:1998(E) ISO 2 4.3 Conicalflask ,capableofbeingfittedwiththerefluxcondenser(4.7). 4.4 Volumetricflask ,ofcapacity250ml. 4.5 Beaker,ofcapacity250ml,togeth
11、erwithamagneticormechanicalstirrer. 4.6 Burette,ofcapacity50ml. 4.7 Refluxcondenser . 4.8 Analyticalbalance ,capableofweighingtothenearest0,01g. 4.9 pHmeter ,accuratetoatleast0,05pHunits. 4.10 Waterbath . 5Sampling Itisimportantthelaboratoryreceiveasamplewhichistrulyrepresentativeandhasnotbeendamage
12、dorchanged duringtransportorstorage. SamplingisnotpartofthemethodspecifiedinthisInternationalStandard.AsthereisnospecificInternational Standarddealingwithfruitandvegetableproducts,itisrecommendedthatthepartiesconcernedcometoan agreementonthesubject. 6 Preparationoftestsample 6.1Liquid products Liqui
13、dproductsincludeproductsfromwhichtheliquidiseasilyseparable(e.g.juices,cannedfruitsyrups,pickling liquids,brines,liquidsfromfermentedproducts). Takepartofthepreviouslymixedlaboratorysampleandfilteritthroughcottonwool,filterpaperorcloth.Transfer, bymeansofthepipette(4.2),25mlofthefiltrate(seenote)int
14、othevolumetricflask(4.4).Dilutetothemarkwith waterandmixthoroughly. Itisnecessarytoremovecarbondioxidefromcarbonatedliquidproductsbyshakingunderreducedpressurefor 3minto4min. NOTE Itisalsopossibletotakeasamplebymass,weighing,tothenearest0,01g,atleast25gofthelaboratorysample. 6.2Other products Remove
15、anystalks,stones,hardseedcavitywallsand,wheneverpossible,pips(afterthawinginthecaseoffrozen ordeepfrozenproducts).Mixthesamplethoroughly. Allowfrozenordeepfrozenproductstothawinaclosedvesselandaddtheliquidformedduringthisprocesstothe productsbeforemixingorblending. Inthecaseofdehydratedordriedproduc
16、ts,cutapartofthelaboratorysampleintosmallpieces. Homogenizetheproductorgrinditinthemortar(4.1). Weigh,tothenearest0,01g,atleast25gofthelaboratorysampleandtransferittotheconicalflask(4.3)with 50mlofhotwater.Mixwelluntilhomogeneityisobtained. Fittherefluxcondenser(4.7)totheconicalflaskandheattheconten
17、tsonaboilingwaterbathfor30min.ISO ISO750:1998(E) 3 Cool,quantitativelytransferthecontentsoftheconicalflasktoavolumetricflask(4.4)anddilutetothemarkwith water.Mixwellandfilter. 7Procedure NOTE Ifitisrequiredtocheckwhethertherepeatabilityrequirement(clause9)ismet,carryouttwodeterminationsin accordance
18、with7.1.2and7.1.3,or7.2.1and7.2.2. 7.1 Potentiometricmethod(Referencemethod) 7.1.1 CalibrationofthepHmeter CheckthatthepHmeter(4.9)isfunctioningcorrectlyusingthebuffersolutions(3.2). 7.1.2Test portion Transfer,bymeansofthepipette(4.2),25ml,50mlor100mlofthedilutedtestsample(seeclause6),according toth
19、eexpectedacidity,tothebeakerwithitsstirrer(4.5). 7.1.3Determination Startthestirrerandaddquickly,fromtheburette(4.6),thesodiumhydroxidesolution(3.1)untilthepHis7 0,2. Then,slowlyaddmoreuntilthepHis8,1 0,2. 7.2 Methodusingacolouredindicator(Routinemethod) 7.2.1Test portion Transfer,bymeansofthepipett
20、e(4.2),25ml,50mlor100mlofthedilutedtestsample(seeclause6),according totheexpectedacidity,toabeakerwithitsstirrer(4.5). 7.2.2Determination Add0,25mlto0,5mlofthephenolphthaleinsolution(3.3)and,withshaking,titrate,usingtheburette(4.6),withthe sodiumhydroxidesolution(3.1)untilapinkcolour,persistingfor30
21、s,isobtained. 8 Expressionofresults 8.1 Methodofcalculationforlaboratorysamplestakenbyvolume Thetitratableacidity,expressedinmillimolesofH + per100mlofproduct,takingintoaccountthedilutioncarriedout inclause6,isgivenasfollows: 250 V V 1 c 100 1000 00 V Vc V = 1 where V isthevolume,inmillilitres,ofthe
22、testsample,i.e.25ml; V 0 isthevolume,inmillilitres,ofthetestportion(7.1.2or7.2.1); V 1 isthevolume,inmillilitres,ofthesodiumhydroxidesolution(3.1)usedforthedetermination(7.1.3or 7.2.2); c istheexactconcentration,inmolesperlitre,ofthesodiumhydroxidesolution(3.1). Reporttheresulttoonedecimalplace.ISO7
23、50:1998(E) ISO 4 8.2 Methodofcalculationforlaboratorysamplestakenbymass Thetitratableacidity,expressedinmillimolesofH + per100gofproduct,takingintoaccountthedilutioncarriedout inclause6,isgivenasfollows: 250 m V 1 c 100 0 V where V 0, V 1 and chavethesamemeaningsasin8.1; m isthemass,ingrams,ofthetes
24、tsample(see6.1anditsnote,or6.2). Reporttheresulttoonedecimalplace. 8.3 Othermethodsofexpression Itisalsopossibletoexpressthetitratableacidityconventionallyingramsofacidper100gorper100mlofproduct, asappropriate,bymultiplyingtheformula(8.1or8.2)byafactorappropriatetotheacid(seetable1). Table1 Acid Fac
25、tor Malicacid Oxalicacid Citricacidmonohydrate Tartaricacid Sulfuricacid Aceticacid Lacticacid Citricacid 0,067 0,045 0,070 0,075 0,049 0,060 0,090 0,064 9Repeatability Theabsolutedifferencebetweentwoindependentsingletestresults,obtainedusingthesamemethodonidentical testmaterialinthesamelaboratoryby
26、thesameoperatorusingthesameequipmentwithinashortintervaloftime, willinnotmorethan5%ofcasesbegreaterthan2%ofthearithmeticmeanofthetworesults. 10Test report Thetestreportshallspecify: allinformationnecessaryforthecompleteidentificationofthesample; thesamplingmethodused,ifknown; thetestmethodused,toget
27、herwithreferencetothisInternationalStandard; alloperatingdetailsnotspecifiedinthisInternationalStandard,orregardedasoptional,togetherwithdetailsof anyincidentswhichmayhaveinfluencedthetestresult(s); thetestresult(s)obtained; iftherepeatabilityhasbeenchecked,thefinalquotedresultobtained.ISO750:1998(E) ISO ICS67.080.01 Descriptors: agriculturalproducts,foodproducts,plantproducts,fruitandvegetableproducts,tests,determination,acidity. Pricebasedon4pages
