Hydrolysis of αs- and β-caseins during ripening of Serra cheese

Hydrolysis of the major caseins in Serra cheese manufactured from raw sheepʹs milk coagulated with a plant rennet (Cynara cardunculus, L.) was monitored by urea-PAGE electrophoresis throughout a 35 day ripening period (with sampling at 0, 7, 21 and 35 days) and throughout the cheesemaking season (with sampling at November, February and May). The αs- and β-caseins were degraded up to 82 and 76%, respectively, by 35 days of ripening. The αs-casein variants (αs2- and αs3-) displayed similar degradation patterns to one another, but different from those of β-casein variants (β1- and β2-). Although the αs-caseins were broken down more slowly than β-caseins at early stages of ripening (97, 95, 80, and 60% of αs2-, αs3-, β1-, and β2-caseins, respectively, were still intact by 7 days), this observation was reversed for later stages of ripening (18, 18, 30, and 20% of αs2-, αs3-, β1− and β2-caseins, respectively, were still intact by 35 days of ripening). The position along the cheese-making season significantly affected the hydrolysis of only the β2- and αs3-caseins. Degradation of αs3-casein was slower in February than in November or May for 21-day old cheeses; cheeses ripened for 7 days or 21 days showed more intact β2-casein when manufactured in May than in November or February. The magnitude of the correlation coefficients pertaining to concentrations of intact αs- and β-caseins indicated that the products of proteolytic breakdown with higher mobility than αs-caseins (tentatively termed α1-I, α2-I, and α3-I) were preferentially correlated with αs-caseins, the products of proteolytic breakdown with mobility between β-caseins and αs-caseins (tentatively termed β1 and β1-I) were preferentially correlated with β1 and β2-caseins rather than with αs-caseins, and the products of proteolytic breakdown with the highest mobility (tentatively termed αβ1-II and αβ2-II) were preferentially correlated with β-caseins.