Evaluation of the effect of rennet type on casein proteolysis in an ovine milk cheese by means of capillary electrophoresis.

Capillary electrophoresis was used to study the evolution of casein throughout the ripening process of Roncal Denomination of Origin ewe's milk cheese and to assess the type of rennet in its hydrolysis. Two manufactures were prepared, each with four vats; two of them had added lamb artisan rennet, batch A [clotting activity of 97.54 rennet units (RU) ml(-1)] and batch B [clotting activity of 16.26 RU ml(-1)]; one vat included calf industrial rennet, batch I (clotting activity of 45.70 RU ml(-1)); and the fourth vat had added mixed rennet, batch M, a 50:50 mixture of lamb (batch A) and calf (batch I) (clotting activity of 77.53 RU ml(-1)). The content of casein nitrogen in fractions alpha-casein1CE, alpha-casein2CE, beta-casein1CE and beta-casein2CE was quantified in cheese after 1, 15, 30, 60, 120 and 180 days of ripening. Beta-casein fractions undergo lesser degradation during the ripening time than alpha-casein proteins. The degradation of alpha-caseins is very much influenced by the clotting activity of the rennet used, so that the more active the clotting activity the greater the hydrolysis of those caseins. Nevertheless, it is at the level of beta-caseins that we observe the evidence of the influence of the type of rennet, thus noting a less intense proteolytic activity in the batch made with calf rennet, batch I.