The nature of beta-casein heterogeneity in caprine milk

The heterogeneity of some caprine fH:asein patterns was studied using gel electrophoresis at alkaline pH, isoelectric focusing on polyacrylamide gel, immunoblotting with polyclonal antibodies against fH:asein and electrospray mass spectrometry. It was demonstrated that the origin of this heterogeneity depended on multiple phosphorylation of the peptide chain giving 4P, 5P and 6P forms. Caprine Us,-easein was also found in 3 phosphorylated forms, 7P. 8P and 9P. Individual caprine milks which did not contain the Il-casein fraction were also identified, as were milks containing reduced amounts of this protein. Using comparative assays on the aptitude of individual milks to coagulate, it was demonstrated that ~-null milks presented longer rennet coagulation times than normal milks and that curd firmness was consistently poorer.