Microwave irradiation: Effect on activities and properties of polyphenol oxidase in grape maceration stage

Abstract In this work, the microwave was used to investigate the changes in activities and the possible passivation mechanism of PPO during the maceration stage of winemaking at different microwave conditions. Under the condition of microwave power 500 W, temperature 50 °C, and time 8 min, the activity of PPO decreased 0.853 U/(g·min) in grape maceration solution, having a decrease of 39.58% compared to the untreated PPO. The carbon-centred free radicals were induced in PPO solution at different microwave conditions. Besides, the changes of PPO conformational properties confirmed that microwave did affect the activity of PPO by influencing the PPO's composition, microenvironment, groups, chemical bonds, structure, and hydrolysis degree. The study will contribute to understanding the mechanism of higher extraction rate of phenols compounds in the maceration stage of winemaking by microwave irradiation.