Contribution of plasmin to primary proteolysis during ripening of cheese: effect of milk heat treatment and cheese cooking temperature

Abstract

The effects of milk heat treatment and cooking conditions during cheese manufacture on plasmin activity and proteolysis during ripening were determined. Milk heat treatments studied were raw (no heating), 63 o C for 30 min and 75 o C for 1, 5 or 10 min. In separate experiments, cooking tem- peratures of 38, 43, 48 and 55 o C were examined. Varying cooking temperature did not significantly affect cheese composition except that moisture content was significantly lower (P < 0.05) at higher cooking temperatures and salt content also significantly (P < 0.001) differed between treatments. In- creasing cooking temperature increased plasmin activity and plasminogen activation during ripen- ing, but decreased chymosin activity, as seen from urea-PAGE analysis. Increasing severity of milk heat treatment had no significant effects on cheese composition, but decreased plasmin activity in cheese and, overall, had less significant effects on proteolysis during ripening than cooking condi- tions. Thus, the importance of activators and inhibitors of the plasmin system, and their heat stability, in cheese ripening, and the effect of processing, conditions thereon, were apparent. cheese / pasteurisation / cooking / plasmin / proteolysis