Effects of incubation temperature and salt concentration on plasminogen activators in cheese curd

Plasmin (PL) can play a major role in the proteolysis of dairy products, especially during cheese ripening. The effects of cook temperature and salt concentration on PL in cheese systems have been studied; however, the effects of cheese making conditions on plasminogen activators (PAs) have not. Therefore, the objective of this study was to determine the effect of curd cook temperature and salt concentration on PL, plasminogen (PG), and PAs. PL, PG, and urokinase-type PA activities extracted from cheese curds cooked at 21 °C were significantly (P⩽0.05P⩽0.05) lower than those extracted from cheese curds cooked at 37 or 55 °C. Activity assays showed that PG was the only component in the PL enzyme system that was significantly affected by salt concentration, with higher PG-derived activity at 0% NaCl than 5% NaCl. Specialized electrophoresis confirmed that PL and PA activities increased with increasing cook temperature, and, unlike the activity assays, indicated that increase in salt concentration (to a certain extent) could increase PL and tissue-type PA activities.