MONITORING CHEDDAR CHEESE RIPENING BY CHEMICAL INDEXES OF PROTEOLYSIS .2. PEPTIDE-MAPPING OF CASEIN FRAGMENTS BY REVERSE-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The proteolysis of casein during cheese ripening was studied by reverse-phase (RP)-HPLC peptide mapping. Cheddar cheese from two different production plants were analysed during a 6-month ripening period at 4-degrees-C and 10-degrees-C. The elution profile obtained from cheese extracts soluble at pH 4.6 contained more than 120 peaks. These were grouped into four ranges of molecular mass (I < 3000 Da; II > 30 000 Da; III > 10 000 Da; IV > 3000 Da) by RP-HPLC of cheese extracts fractionated by ultrafiltration at different molecular mass cutoffs. The peptide patterns, especially in the molecular mass range below 3000 Da, were clearly dependent on ripening time and temperature, manufacturing history, and composition of the cheese. Several short chain peptides with less than ten amino acid residues were isolated, sequenced for identification, and assigned to the corresponding amino acid sequences of alpha(s1)-casein and beta-casein. The levels and ratios of these defined marker peptides seem to be well suited for in-depth characterisation of proteolysis and ripening of Cheddar cheese. This information is fundamental for studies on cheese origin, flavour, taste, and texture.