Peptides identified during emmental cheese ripening:: Origin and proteolytic systems involved

To determine the proteolytic changes occurring during Emmental cheese ripening, peptides released in cheese aqueous phase were analyzed by reversed-phase HPLC and identified by tandem mass spectrometry sequencing, for which different strategies were illustrated by some examples. Among the 91 peptides identified, most of them arose from alpha (s1)- (51) and beta -caseins (28), and a few arose from alpha (s2)- (9) and kappa -caseins (1). An attempt was made to correlate the released peptides with the proteolytic systems potentially involved during Emmental cheese manufacture. Besides the well-known action of plasmin on beta- and alpha (s2)-caseins, and in the absence of residual fungal coagulant from Endothia parasitica, two other proteinases seem to be involved in the hydrolysis of alpha (s1)-casein in Emmental cheese: cathepsin D originated from milk and cell-envelope proteinase from thermophilic starters. Moreover, peptidases from starters were also active throughout ripening, presumably like those from nonstarter lactic acid bacteria, in contrast to those from propionic acid bacteria.