Carboxyl-Modified Porcine Pepsin: Properties and Reactions on Milk and Caseins

Abstract

Reactions of carboxyl-modified pepsin on milk and caseins were studied. Although caseinolytic properties of the enzyme were not affected by modification, clotting activity against κ-casein was increased while clotting activity against κ-αsl-casein mixture was decreased. The decrease in milk clotting activity may be from a change in the charge distribution on the modified enzyme, thus hindering the interaction between pepsin and micelles.The stability of the modified enzyme was improved markedly in .05 M phosphate buffer at pH 6.5 and in milk ultrafiltrate under simulated cheese-making conditions. The thermal stability of pepsin in terms of milk clotting also was improved. The quality of the curds was not affected by the modification and was comparable to that of chymosin curds. The modified enzyme may be a more suitable rennet substitute than native pepsin in cheese-making.