Plasmin activity in high-pressure-homogenised bovine milk

This study investigated changes in plasmin activity in raw whole bovine milk induced by high-pressure homogenisation (HPH) at 50-200 MPa. Previous studies have reported that such treatment inactivates large amounts of plasmin in milk. However, HPH-induced reductions in plasmin activity were not observed when the surfactant Tween 80 was added to milk, either prior to or post HPH. Hence, the results of the present study reveal that previously reported HPH-induced reductions in plasmin activity in milk are primarily due to centrifugal removal of milk lipid globule membrane-associated plasmin from the assay mixture, rather than actual inactivation of the enzyme. The outcomes of this study stress the need to carefully evaluate analytical methods when applying novel processing technologies to milk and warrant reconsideration of the previously assumed suitability of HPH to inactivate indigenous enzymes in milk. Furthermore, the results of this study stress the importance of the inclusion of milk fat globule membrane material in assaying for plasmin activity in milk, particularly in homogenised milk products.