The inactivation kinetics of polyphenol oxidase and peroxidase in bayberry juice during thermal and ultrasound treatments

Ultrasound is recognized as a non-conventional processing technology for food preservation and quality improvement. Effects of thermal and ultrasound treatment on the inactivation kinetics of polyphenol oxidase (PPO) and peroxidase (POD) in bayberry juice were studied. Whether cooling with ice bath during ultrasound treatment was conducted to separate effects of heat and cavitation effects. In all processes, the inactivation kinetics of PPO and POD followed a first-order model (R-2 = 0.864-0.997). The D-T value during thermal inactivation varied from 151.99 to 6.23 min for PPO and the corresponding Z(T) values and activation energy (Ea) were 13.16 degrees C and 166.77 kJ/mol, while those parameters of POD were 298.26-7.08 min, 14.25 degrees C and 153.49 kJ/mol, respectively. The ultrasound (US) inactivation rate constants (k) for PPO ranged from 0.0556 min(-1) to 0.8878 min(-1) with the corresponding D values of 41.44-2.59 min and Z(UI) values of 312.50 W/cm(2). However, the k value of PPO during ultrasound with cooling (USC) decreased to 0.0412-0.3268 min(-1), while the D and Z(UI) values increased to 55.92-7.05 min and 432.90 W/cm(2), indicating that the heat brought out during ultrasound treatment significantly enhanced the inactivation kinetics of PPO. The inactivation rates of POD by US treatment were also higher than those by USC at the same ultrasound intensity and time. In addition, the kinetic parameters for POD by US and USC treatment were lower than those of PPO, inferring its more sonication resistant. Industrial relevance: Ultrasound is a non-thermal food processing method for microorganism and enzyme inactivation, as well as quality maintenance. Attractive color is one of the most important quality attribute of bayberry products and strongly affects the consumer acceptance and preference. A key role in color degradation in berry fruit products is attributed to enzymatic browning of phenolic compounds which mainly related to PPO and POD. Therefore, the inactivation of PPO and POD is necessary for better color retention and shelf life increasing. This study would provide technical support for PPO and POD inactivation of ultrasound technique in bayberry juices processing.