Ultrafiltration of cheese milk: Effect on plasmin activity and proteolysis during cheese ripening

Havarti 45+ cheese was manufactured from milk concentrated 1.8–4.6-fold by ultrafiltration (UF) and from normal milk, and the effect of concentration factor on plasmin activity and subsequent proteolysis in cheese during ripening was examined. There was decreased plasmin activity and a reduced rate of proteolysis of αS2-casein and β-casein in the UF-cheeses, compared with the corresponding controls, independent of concentration factor. The decreased plasmin activity and slower breakdown of αS2-casein and β-casein in UF-cheeses compared with traditional cheeses can be partly explained by the inclusion of an increased amount of plasmin inhibitors into the UF-cheeses. However, it is suggested that the differences in plasmin activity and proteolysis arise mainly as a result of inactivation of the plasminogen activation system during UF-concentration, due to a combination of time, temperature and the presence of air in the UF-equipment. The effect of milk treatment on the plasminogen activation system should be further investigated.