Heat inactivation of native plasmin, plasminogen and plasminogen activators in bovine milk: a revisited study

Abstract

Thermal inactivation, at temperatures between 60 o C and 140 o C, of native plasmin, plasminogen and plasminogen activators were studied in bovine milk using improved enzymatic as- says. While measured heat inactivation kinetic of plasmin and plasminogen were in line with previ- ously reported values, plasminogen activators were, surprisingly, found to be as heat sensitive as plasmin and plasminogen in a milk system containing proteins with free SH groups. Activation ener- gies (Ea) for the heat denaturation of plasmin, plasminogen and plasminogen activators were 29, 35 and 24 kJ.mol -1 , respectively, in the temperature range 95-140 o C , and 244, 230 and 241 kJ.mol -1 , respectively, in the temperature range 70-90 o C. The heat inactivation of the whole plasmin system in milk appeared to be directly influenced by the presence of β-lactoglobulin. The rate of plasmin inacti- vation during long heat treatments decreased rapidly, probably because of the disappearance of avail- able β-lactoglobulin for S-S linking. plasmin / plasminogen / plasminogen activator / heat inactivation / milk