γ-Casein as a Marker of Ripening and/or Quality of Grana Padano Cheese

Several biochemical reactions occur in cheese during ripening. Among these, proteolysis of β-casein to produce γ fractions is one of the most evident. In search of new quality markers, an isoelectric focusing technique in a suitable pH range has been used to evaluate γ-casein profiles in Grana Padano cheese samples at different times of ripening (from 4 to 36 months). The following ratios between densitometric values were considered: γ2-casein/γ1-casein, γ3-casein/γ1-casein, and γ3-casein/ γ2-casein. Another parameter investigated was the presence of modified γ2-casein (with pI = 6.7), which derives from the interaction between γ2-casein and aldehydes coming from microbial metabolism. The appearance of this protein band correlates well with the cheese ripening period. Data shown in this paper indicate that γ fractions could be considered as new markers of ripening and quality and contribute to the certification of Grana Padano cheese on the international market.