STUDY OF PROTEOLYSIS DURING STORAGE OF RAW-MILK AT 4-DEGREES-C - EFFECT OF PLASMIN AND MICROBIAL PROTEINASES

In order to study the intel actions between microbial proteinases and plasmin, and their effects on milk quality during storage at 4 degrees C, experiments were conducted on four milks treated as follows: control milk, milk with added urokinase, milk with added urokinase and bacteriocide, and milk with added bacteriocide. Microbial growth, pH, nitrogen components, total proteolysis, plasminogen-plasmin activity microbial proteinase activity, casein-fraction composition and colloidal minerals were measured during six days of storage. This study on proteolysis in milk during storage at 4 degrees C for six days points to the greater importance of microbial proteinases than plasmin at this temperature. Among the physico-chemical parameters, pH and casein level of milks without bacteriocide decreased after the fourth day of storage when the bacterial count leached 10(6) to 10(7) cfu mL(-1). No activation of plasminogen to plasmin by natural activators or by microbial proteinases was observed. Plasmin and plasminogen-plasmin activities decreased during the six days of storage at 4 degrees C.