EFFECT OF MODIFICATION OF AMINO-GROUPS ON CROSS-LINKING OF CASEIN BY MICELLAR CALCIUM-PHOSPHATE

Bovine alpha(s1)-CN was acetylated, succinylated, and citraconylated. Artificial casein micelles (alpha(s1)-kappa-CN micelles) were prepared at a casein concentration of 2.5% with 20 to 50 mM calcium, 17 to 27 mM phosphate, and 10 mM citrate, and crosslinking of casein by micellar calcium phosphate was examined by HPLC in the presence of 6 M urea. The content of casein aggregates that were crosslinked by micellar calcium phosphate in modified alpha(s1)-kappa-CN micelles was lower than that in intact alpha(s1)-kappa-CN micelles. Urea-insoluble calcium phosphate was present in succinylated alpha(s1)-kappa-CN micelles, suggesting that it did not participate in crosslinking. The modified alpha(s1)-CN was less crosslinked by micellar calcium phosphate than intact alpha(s1)-CN, even when modified alpha(s1)-CN coexisted equivalently with intact alpha(s1)-CN in artificial casein micelles. The amino groups also affected crosslinking of casein by micellar calcium phosphate.