Proteolysis of beta-casein as a marker of Grana Padano cheese ripening

Proteolysis has a critical role in defining the typical organoleptic characteristics of Grana Padano, a wellknown Italian cheese. During the ripening process, hydrolysis of beta-casein produces different fragments, the most abundant and widely studied of which are gamma-caseins, three polypeptides containing the HOOC-terminal portion of beta-casein. By sodium dodecyl sulfate-PAGE and a specific anti-beta-casein monoclonal antibody, two beta-casein-derived bands were identified in Grana Padano cheese: ? a and ? b. Thanks to the identification of the amino acid sequences, it was shown that: a) beta a contains gamma 1-casein [beta-casein (29-209)] and the correlated peptide [beta-casein (30-209)]; b) beta b contains gamma 2-casein [beta-casein (106-209)] and gamma 3-casein [beta-casein (108-209)]. The production of beta a and beta b by the three enzymes most involved in cheese proteolysis (pepsin, chymosin, and plasmin) was evaluated by performing in vitro digestions. A significant correlation between abundance of some polypeptides and ripening process was shown.