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.