pH-Induced dissociation of bovine casein micelles. I. Analysis of liberated caseins

Summary The dissociation of caseins of different types from casein micelles in milk, acidified to different pH values in the range 4·9–6·7, and at temperatures of 4, 20 and 30 °C, has been studied. In contrast to a number of previous findings, it was shown that caseins of all types were dissociated from the micelles, although in all cases β-casein was in highest concentration. The amounts and proportions of all of the caseins were found to be pH- and temperature-dependent, especially the former. Studies of the proportions of the different caseins liberated suggested that, at a defined temperature, the proportions of κ;- and α s2 -caseins were independent of pH, while the proportions of β- and α sl -caseins were variable, changes in one being compensated by changes in the other. The manner in which the proportions of the α sl -casein and β-caseins changes with pH was found to be temperature-dependent.