CHARACTERIZATION OF THE OLIGOPEPTIDES OF PARMIGIANO-REGGIANO CHEESE SOLUBLE IN 120 G TRICHLOROACETIC ACID/L

The non-protein nitrogen (NPN) of samples of Parmigiano-Reggiano cheese ripened for 6 and 15 months was fractionated by ion-exchange chromatography on a Cu2+-Chelex column to separate oligopeptides from free amino acids. Peptide components were isolated by reversed-phase HPLC and identified by fast atom bombardment-mass spectrometry (FAB-MS). Only the NPN fraction of 6 month old cheese samples contained enough peptides to be further characterized. On the basis of FAB-MS spectral results, 39 oligopeptides were identified, the main components being phosphopeptides. Two sets of both intact and partly dephosphorylated peptides, accounting for a total of 19 phosphopeptides, were formed by the hydrolysis of p-casein and belonged to regions 1-20 and 6-28 of beta-casein. The formation and potential role of these peptides in cheese is discussed.