Proteolysis indices related to cheese ripening and typicalness in PDO Grana Padano cheese

Different chemical indices related to proteolysis and ripening time have been investigated in Grana Padano (n = 155) and Parmigiano-Reggiano (n = 27) cheese samples using ion-exchange chromatography and capillary electrophoresis. Levels of intact caseins, g-casein and free amino acids in cheese were not strictly related to the maturation period, varying among samples of the same age. A peptide, identified by HPLC/electrospray ionization-mass spectrometry as pyroglutamyl-g3-casein, resulted from cyclisation of N-terminal glutamic acid into a pyroglutamic acid residue. Based on the peak area ratio of pyroglutamyl-g3-casein and g3-casein, an equation, suitable for determination of the cheese age, is proposed. The commercial classes of Grana Padano ripened over 16 and 20 months can be identified by adopting a minimum threshold value for this peak area ratio.