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1、JournalofDairyResearch(1979),46,433-439433Inorganicconstituentsofmilk:I.CorrelationofsolublecalciumwithcitrateinbovinemilkBYCARLHOLTANDD.DONALDMUIRHannahResearchInstitute,Ayr,ScotlandKA65HL(Received4August1978)SUMMARY.Ahighcorrelationwasfoundbetweensolublecal
2、ciumandcitrateconcentra-tionsduringastudyofseasonalchangesinthecompositionofthecommercialmilksupplytoSouth-westScotland.Asimplephysicochemicalmodeloftheionequilibriaintheaqueousphaseofmilksuggeststhattheobservedcorrelationiscausal.Thishypo-thesiswascorroborat
3、edbyananalysisofdataonindividualcowmilksandbyexperimentsinvolvingtheadditionofcitratetomilkatconstantpH.TherehavebeenmanyadvancesinunderstandingofthechemistryoftheinorganicconstituentsofmilksincethereviewofWright(1929).Thechangesinmilksaltconcentrationwhichar
4、eassociatedwithstageoflactationandlactationnumberarenowwelldocumented(White&Davies,1958;Rook&Campling,1965)asisthewayinwhichmilksaltsarepartitionedbetweentheaqueousandcolloidalphases(White&Davies,1958;Pyne,1962).Inadditiontothisempiricalknowledge,someprogress
5、hasalsobeenmadeinunderstandingthemechanismscontrollingtheultimateconcentrationsofsomeoftheinorganicconstituentsinmilk.Forexample,corre-lationsbetweenNa,KandClconcentrationsandthelactosecontentofmilk(Barry&Rowland,1953;Rook&Wood,1959)mayberationalizedintermsof
6、ionmovementsacrossthemammaryepithelium(Rook&Wheelock,1967;Linzell&Peaker,1971a,b;Peaker,1975)andmaintenanceofmilkinosmoticbalancewiththemammaryglandbloodsupply(Rook&Wood,1959;Walsh&Rook,1964).However,thereisnocorrespondinglydetailedunderstandingoffactorsinflu
7、encingtheconcentrationsofCa,Mg,inorganicorthophosphate(P^andcitrate(Cit)inmilk.InareportofthefirstphaseofasurveyofthecompositionofthecommercialmilksupplyinSouth-westScotland,considerableseasonalvariationintheCacontentofbulkmilkwasobserved(Holt&Muir,1978;Holt,
8、Muir&Sweetsur,1978).Consequently,duringthesub-sequentphaseofthesurvey,moredetailedanalyseswerecarriedout.Somepre-liminaryresultsarepresentedherewhichdemonstrateastrongcorrelationbetweenCa
