THERMAL INACTIVATION KINETICS OF LACTOPEROXIDASE IN MODEL SYSTEM, MILK AND WHEY

Abstract

Inactivation of lactoperoxidase (LPO) in model system, milk and whey at atmospheric pressure was studied in a temperature range of 60-70 °C. The first order kinetics model allowed the estimation of the inactivation rate constants (k) and the thermal death times (D). D- and k-values decreased and increased, respectively with increasing temperature, indicating a more rapid LPO inactivation at higher temperatures.  At 70°C the inactivation of LPO was achieved in milk after 6 minutes and in whey after 4 minutes of thermal treatment. At 67.5°C lactoperoxidase was completely inactivated after 14 minutes in phosphate buffer. In all systems studied the temperature dependence of lactoperoxidase inactivation in milk, whey and model system versus the reaction rates could be accurately described by the Arrhenius equation. The estimated activation energies were of 155.67 kJ/mol for phosphate buffer, 217.79 kJ/mol for milk and 235.57 kJ/mol for whey. The correspondent z_T values were estimated with the thermal death model and the values obtained were very close for all the three systems studied. For all the loglinear regression equations calculated SAS System for Windows 9 software was used. Lactoperoxidase is an important antimicrobial system and knowing its thermostability in milk, byproducts and model systems allows a better control of the enzyme activity.