Characterization of the oligopeptides of Parmigiano-Reggiano cheese soluble in 120 g trichloroacetic acid/1

Abstract

SummaryThe 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 β–casein and belonged to regions 1–20 and 6–28 of β–casein. The formation and potential role of these peptides in cheese is discussed.