THE NATURE OF BETA-CASEIN HETEROGENEITY IN CAPRINE MILK

The heterogeneity of some caprine beta-casein patterns was studied using gel electrophoresis at alkaline pH, isoelectric focusing on polyacrylamide gel, immunoblotting with polyclonal antibodies against B-casein 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 alpha(s1)-casein was also found in 3 phosphorylated forms, 7P, 8P and 9P. Individual caprine milks which did not contain the beta-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 beta-null milks presented longer rennet coagulation times than normal milks and that curd firmness was consistently poorer.