Camel and Bovine Chymosin Hydrolysis of Bovine αS1- and β-Caseins Studied by Comparative Peptide Mapping

In Many, cheese varieties, the general proteolytic: activity of the coagulant is of,great importance to the development of flavor and texture dining ripening.:This study used capillary electrophoresis and LC-MS/MS to compare the in vitro proteolytic behaviour of camel and bovine chymosin (CC/BC) on bovine at alpha(S1)- and beta-casein (CN) at pH 63 and 30 degrees C. beta-CN hydrolysis was also studied at pH 5.2 and in the presence of 0,2, and 5% (w/v) NaCl. A total of 25 alpha(S1)- and 80 beta-CN peptides were identified, and rates of early peptide formation were determined. The modes Of proteolytic action of CC and BC shared a high degree of similarity generally. However, except for a few peptide bonds, CC was markedly less active, the magnitude of which varied widely With cleavage site Preferential alpha(S1)-CN (Phe23-Phe24) and beta-CN (Leu192-Tyr193) hydrolysis by CC proceeded at an estimated 36 and 7% of the initial rate of BC, respectively. The latter rate difference was largely pH and NaCl independent Several cleavage sites appeared to be unique to :CC. and especially BC action, but qualitative difference's were often predetermined by quantitative effects: In particular, negligible CC affinity to alpha(S1)-CN164/165 and beta-CN189/190 prevented further exposure of the N-terminal products beta-CN hydrolysis by either enzyme was always stimulated at the lower yet either inhibited or stimulated by the presence of NaCl, depending mainly on the predominating type Of molecular substrate interactions involved at the specific site Of cleavage. The potential impact of this proteolytic behavior on cheese. quality is discussed.