Effect of high-pressure jet treatment on the plasmin system in milk

Plasmin persists in many dairy products, leading to undesirable quality defects. High pressure jet (HPJ) processing may be a potential method to reduce the plasmin (PL) activity due to its strong shear and high pressure. However, the impact of HPJ processing on the activity of PL-system remains unknown. In the study, the activities of PL and plasminogen (PG) in raw milk treated with HPJ were evaluated. PL activity increased from 127.24% to 180.21% in milk treated HPJ at 100-300MPa for single-cycle. Meanwhile, HPJ processing increased the PG activators (PA) activity and reduced the PA inhibitors (PAI) activity, suggesting that the increase of PL activity was caused by the conversion of PG to PL. Furthermore, milk treated with HPJ at 200 MPa or 300 MPa for three cycles can substantially decrease the activities of PL and PG. The initial TPC values in milk decreased from 1.37 × 104 CFU/mL to 8.00 × 101 and 2.00 × 101 CFU/mL. Overall, these results suggested that increasing the cycle number is an effective method to inhibit PL activity and achieve sterilization, which provided preliminary mechanistic insights into the effects of HPJ treatment on the PL-system in milk.