Quality control of grated Parmesan products using an electrophoretic ripening index.

摘要

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 PAGE (pH 8.9, 5 M urea) was followed by the densitometric analysis of the gamma- and beta-casein ( -Cn) fractions. The coefficients (gamma-Cn/beta-Cn) and the beta-Cn contents of 68 grated Parmesan samples labelled as Parmigiano-Reggiano, Grana Padano and Original Italian Parmesan cheese taken from retailoutlets in Italy and Austria were determined. Samples from Italy were generally found to be of good quality. However, most of the samples from Austria showed surprising electrophoretograms, which were similar to those of very young Grana Padano cheese or to whole reference casein. Unexpectedly, intense bands of alphas1- and beta-casein, but only a very low proportion of degradation products were detected. This was probably due to adulteration with products with low proteolysis (cheese rind or very young cheese), which could be shown by urea-PAGE analysis of individual particles of grated Parmesan samples and of succeeding cheese rind-layers of a block of Grana Padano cheese. Using standard mixtures, the effect of the relative percentage of rind on thedegree of proteolysis and the apparent age of artificially-adulterated grated Parmesan samples as deducted from the (gamma-Cn/beta-Cn) coefficient was shown.