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 extent of solubilization of colloidal calcium phosphate and dissociation of caseins from the micelles were examined. As the pH was reduced, calcium phosphate was progressively removed from the micelles, and after each pH adjustment there was an initial rapid increase in serum concentrations of Ca and inorganic phosphate, but only a slight further increase on storage. The extent of disssociation of the caseins from the micelles on acidification was temperature-dependent. At 30 °C, concentrations of serum casein remained low, but at 20 °C, and especially at 4 °C, the levels of all 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 increase in the serum concentrations of the caseins and a more gradual increase on storage up to 24 h.