Plasminogen activation in cheese milk: Influence on Swiss cheese ripening

Our objective was to increase plasmin activity, proteolysis, and flavor development of Swiss cheese. Swiss cheese was manufactured from milk containing no added urokinase (control), low concentrations of urokinase (0.05 U/L), or high concentrations of urokinase (0.5 U/L). Composition of cheese, plasmin activity, and urea-PAGE of cheese proteins were analyzed after 6, 12, and 24 wk of ripening. Sensory evaluation and HPLC analysis were done after 12 and 24 wk. Plasmin activity increased in Swiss cheese made from milk that contained high concentrations of urokinase. Urea-PAGE showed that higher plasmin activity resulted in more rapid hydrolysis of beta-casein during 12 wk of ripening. After 24 wk, there were no differences in beta-casein contents among the cheeses. Sensory evaluation showed that propionic acid, nutty flavor, and overall flavor intensity were higher for cheese ripened for 12 wk and made from milk that contained urokinase. After 24 wk, there were no sensory differences among cheeses.