EQUILIBRIUM BETWEEN THE PROTEIN MATRIX AND THE SERUM PHASE OF PRATO CHEESE

A Survey of the Peptide Profile in Prato Cheese as Measured by MALDI-MS and Capillary Electrophoresis

In this study, we describe the characterization of the peptide profile in commercial Prato cheese by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and capillary electrophoresis (CE). Ten commercial Prato cheese brands were characterized via their physicochemical composition and subjected to fractionation according to solubility at pH 4.6. The pH 4.6 insoluble fraction was evaluated by CE, whereas MALDI-MS was applied to the fraction soluble at pH 4.6 and in 70% ethanol. CE revealed a characteristic pattern of hydrolysis, with formation of para-κ-casein, hydrolysis of α_s1 -casein at the Phe₂₃ - Phe₂₄ bond, and hydrolysis of β-casein. For the MALDI-MS data, a complex peptide profile was observed, with the identification of 44 peptides previously reported (24 peptides from α_s1 -casein, 14 from β-casein, 3 from κ-casein, and 3 from α_s2 -casein). It was also observed that cheeses with salt-in-moisture content greater than 5% showed an accumulation of a bitter-tasting peptide (m/z 1536, α_s1 -CN f1-13), suggesting a relationship between the higher salt concentration and the abundance of this peptide. In conclusion, the results showed that even commercial cheeses produced with different raw material and processing conditions showed very similar peptide profiles when assessed at the molecular level, and only 9 peptides were responsible for discrimination of cheeses.