Effects of acidification and storage of milk on dissociation of bovine casein micelles

The effects of acidification and storage of skim-milk on the rate and exten t of solubilization of colloidal calcium phosphate and dissociation of case ins from the micelles were examined. As the pH was reduced, calcium phospha te was progressively removed from the micelles, and after each pH adjustmen t there was an initial rapid increase in serum concentrations of Ca and ino rganic phosphate, but only a slight further increase on storage. The extent of disssociation of the caseins from the micelles on acidification was tem perature-dependent. At 30 degrees C, concentrations of serum casein remaine d low, but at 20 degrees C, and especially at 4 degrees C, the levels of al l caseins increased in the serum as the pH was reduced to about pH 5.5 and 5.2, respectively. After each pH adjustment, there was an initial rapid inc rease in the serum concentrations of the caseins and a more gradual increas e on storage up to 24 h.