Application of capillary electrophoresis to the study of proteolysis of caseins

Capillary electrophoresis using a hydrophilically coated capillary and a low pH buffer containing urea has been used to follow the proteolytic action of plasmin and chymosin on isolated casein fractions, whole casein and individual milk samples selected on the basis of their genetic variants. Several of the main casein breakdown products were identified. These included, among others, gamma(1)-casein (CN) A(1), gamma(1)-CN A(2), gamma(1)-CN B, gamma(1)-CN C, gamma(2)-CN A, gamma(1)-CN A(3), gamma(2)-CN B, gamma(3)-CN A and gamma(3)-CN B, as well as proteose peptones, arising from the action of plasmin on the different genetic variants of beta-CN. alpha(s1)-I-CN and alpha(s1)-CN f(1-23) from alpha(s1)-CN, and para-kappa-CN and caseinomacropeptide from kappa-CN produced by chymosin action were also separated. The knowledge of their migration times provided information on the extent and origin of casein hydrolysis in both milk and cheese, as found in samples of proteolysed milk or fresh cheese.