QUALITY-CONTROL OF GRATED PARMESAN PRODUCTS USING AN ELECTROPHORETIC RIPENING INDEX

An electrophoretic ripening index for the evaluation of proteolysis in Parmesan cheese was used for the quality control of commercial grated Parmesan samples. The separation of caseins by alkaline polyacrylamid e gel electrophoresis (PAGE) (12% T, 2.6% C, pH 8.9, 5 M urea) was fol lowed by the densitometric analysis of the gamma- and beta-casein frac tions. The coefficients (gamma-Cn/beta-Cn) as well as the beta-casein contents of 68 grated Parmesan samples labelled as Parmigiano-Reggiano , Grana Padana and Original Italian Parmesan cheese were determined. S amples taken from retail outlets in Italy generally were found to be o f good quality. However, most of the samples retailed in Austria showe d quite surprising electrophoretograms, which were similar to those of very young Grana Padano cheese and whole reference casein, respective ly. Unexpectedly, intense bands of alpha(s1)- and beta-casein, but onl y a very low proportion of degradation products could be detected. Thi s was probably due to the adulteration with products with low proteoly sis (e.g. cheese rind, very young cheese), which could be shown by ure a-PAGE analysis of individual particles of grated Parmesan samples and of succeeding cheese rind-layers of a loaf of Grana Padano, respectiv ely. Using standard mixtures, the effect of the relative percentage of rind on the degree of proteolysis and the apparent age of artificiall y adulterated grated Parmesan samples as deducted from their coefficie nts (gamma-CN/beta-Cn) was demonstrated.