Affinage et qualité du Gruyère de Comté. IV. Etude de la protéolyse

Abstract

The ripening of Gruyere de Comte cheese was studied using 4 factories capable of making 4 identical cheeses from the same vat of milk. Each of these 4 cheeses was ripened in 1 of 4 different ripening rooms. Six trials were conducted during 6 different months in 2 seasons. Overall, 96 cheeses were analysed at 4 successive stages of their maturation. Determinations of plasmin contents of milks were performed, as well as quantitative changes in cheese protein fractions by polyacrylamide-agarose gel electrophoresis. After 3 weeks of ripening, 78.8% of alpha -caseins and 84.2% of beta -caseins remained unhydrolysed and, at the end of ripening, 23.0% of alpha -caseins and 39.8% of beta -caseins were still unhydrolysed. The study showed that casein fractions could be divided into 2 independent groups: 1 group contained the beta -, deg. beta - (2 unidentified electrophorectic fractions released from beta -casein), gamma - and gamma -casein fractions, and a 2nd group contained the alpha and alpha fractions. The gamma -fraction appeared to be independent of the gamma - and gamma -caseins. The amount of alpha was closely related to the temp. of the ripening room. The influence of manufacturing variables (milk composition, starters, technology) was important for the water-soluble peptide fraction, and beta -, deg. beta -, gamma -, gamma - and alpha -fractions. Season significantly affected the products of degradation of beta -casein. Different mechanisms of hydrolysis seem to exist, depending on the season and the temp. of the ripening room. The changes in plasmin levels in milk were compared with the proportions of gamma - and deg. beta -fractions at 2 stages of the ripening of cheeses. [For parts I-III see DSA 50, 4685-4687.]