EFFECT OF HIGH-PRESSURE TREATMENT OF MILK ON LIPASE AND gamma-GLUTAMYL TRANSFERASE ACTIVITY

High-pressure treatment was applied to milk to evaluate the pressure effects on the activities of lipoprotein lipase and gamma-glutamyl transferase, and the extent of enhancement in activity was pressure level dependent, with lower pressure resulting in a greater enhancement.

Abstract

High-pressure (HP) treatment (0–180 min at 300–400 MPa) was applied to milk to evaluate the pressure effects on the activities of lipoprotein lipase and γ-glutamyl transferase. Short time pressure exposure resulted in some enhancement in the activity of both enzymes, and for lipase, there was no inactivation during the entire pressure hold time (up to 100 min). With γ-glutamyl transferase, the extent of enhancement in activity was pressure level dependent, with lower pressure resulting in a greater enhancement. Furthermore, longer pressure treatment times resulted in inactivation of γ-glutamyl transferase, following a first order kinetic model. The pressure sensitivity of the inactivation parameters (k and D-values) for γ-glutamyl transferase was adequately described by the pressure death time and Arrhenius models with a zpof 543 MPa and an associated volume of activation, ΔV≠, of −3.28 × 10−8 m3/mole.