Ultra high pressure pasteurization of milk: Kinetics of microbial destruction and changes in Physico-chemical characteristics

Abstract

This study was carried out to evaluate the ultra high pressure (UHP) pasteurization requirements of milk. Fresh raw milk was subjected to UHP treatment at selected pressures (200-400 MPa) for various holding times (5 to 120 min), and kinetic parameters (rate constant, k and decimal reduction time, D) were evaluated, based on the first order rate model, for the pressure destruction of microorganisms, inactivation of alkaline phosphatase and changes in colour and viscosity. The pressure sensitivities of the kinetic parameters were evaluated based on the Arrhenius-type volume model and the conventional thermal death time-type model. All kinetic behaviours studied were well described by the first order model (R2 > 0.90). As expected, higher pressures resulted in higher rates of microbial destruction, enzyme inactivation as well as colour and flavour changes as indicated by the associated lower D values (and higher k values). Further, the rate of microbial destruction was much more rapid than enzyme inactivation or colour and viscosity changes. The evaluated Arrhenius volume change of activation (ΔV≠) for microorganisms, viscosity, alkaline phosphatase and colour were -3.35, -1.41, -1.39 and -1.054 X 10-5 m3 mol-1, respectively. The pressure z values (zp) for the same variables were 168, 398, 404 and 532 MPa, respectively. Milk subjected to a microbial 4D UHP process at 350 MPa had a shelf-life of 25 d at 0 °C, 18 d at 5 °C and 12 d at 10 °C. ©1997 Academic Press Limited.