ELECTROPHORETIC RIPENING INDEX FOR THE EVALUATION OF PROTEOLYSIS AND THE DEDUCTION OF THE AGE OF PARMESAN CHEESE

We have established an electrophoretic method to evaluate proteolysis in Parmesan cheese by means of an objective ripening index. The separa tion of caseins by alkaline polyacrylamide gel electrophoresis (PAGE) (12% T, 2.6% C, pH 8.9, 5 M urea) is followed by the densitometric ana lysis of the gamma- and beta-casein fractions. The relationship betwee n the resulting coefficients (gamma-Cn/beta-Cn) and the age of referen ce samples of Original Italian Grana Padano (6-22 months) was linear u p to 15 months, allowing an evaluation of the extent of proteolysis an d therefore a deduction of the age of the Parmesan samples analysed. B ased on this calibration we propose to use a threshold level of 1.3 (g amma-Cn/beta-Cn) to verify the required age, i.e. 12 months, of Parmes an cheese, retailed as a loaf or prepacked slices. Commercially grated Parmesan samples may contain less than or equal to 20% cheese rind, w hich has a very low degree of casein breakdown. So a threshold level o f 0.8 (gamma-Cn/beta-Cn) is proposed for all grated Parmesan products. The preparation of reference solutions with defined coefficients (gam ma-Cn/beta-Cn), corresponding to the proteolysis indices of reference samples of different aged Grana Padano is described. The coefficients (gamma-Cn/beta-Cn) as well as the beta-casein content of two additiona l series of reference samples and of 49 commercial Parmesan samples ta ken from retail outlets in Austria and Italy are presented.