Inactivation Kinetics of the Most Baro-Resistant Enzyme in High Pressure Processed Litchi-Based Mixed Fruit Beverage

Abstract

This work focused on a litchi-based mixed fruit beverage, comprising of coconut water and lemon juice, mixed in an optimized proportion. Based on preliminary studies, three resistant spoilage enzymes were identified in the beverage, viz. polyphenol oxidase (PPO), peroxidase (POD), and pectin methyl esterase (PME). The response surface methodology (RSM) based on central composite face-centered design (FCCD) screened out PPO as the most resistant enzyme within the high pressure processing (HPP) domain of 200–600 MPa/30–70 °C/0–20 min. A detailed kinetic study was conducted on PPO inactivation within the same HPP domain along with a set of thermal treatments (0.1 MPa/30–70 °C). A synergistic effect of pressure and temperature on PPO inactivation was observed, throughout the HPP domain. However, PPO was almost completely inactivated at 500 MPa/70 °C/20 min. The inactivation order (n) values for PPO were 1.10 and 1.25 for thermal and HPP treatments, respectively. For every 10 °C rise in temperature, the inactivation rate constant (k, Un-1 min−1) increased approximately by 1.5 times, within 50–70 °C (at 0.1 MPa), while a 10-fold increase was obtained in the case of HPP treatments. The activation energy (E a ) and the activation volume (V a), depicting the temperature and pressure dependence of k, was found to decrease slightly, with an increase in pressure and temperature, respectively. The PPO inactivation rate constant was modeled as a function of both temperature and pressure conditions by combining both Arrhenius and Eyring equations.