Activation and inactivation mechanisms of polyphenol oxidase during thermal and non-thermal methods of food processing

Polyphenol oxidase (PPO) is thought to be a threat to the food industry because it initiates the browning reaction during fruit and vegetables processing. Therefore, thermal and non-thermal technologies such as high hydrostatic pressure, ultrasound and high pressure carbon dioxide are being used effectively to lower the enzymatic activity to get good quality food products. The structural changes and mechanism of PPO inactivation during different food processing techniques have not been reviewed comprehensively. The application of these processing treatments may cause the changes in enzyme structure which have a key role in the inactivation of the enzyme. This review will summarize the current knowledge about PPO activation and inactivation in response to thermal and non-thermal processing of fruits and vegetables. Moreover, the structural changes and possible mechanism of enzyme activation/inactivation after thermal and non-thermal fruits and vegetable processing will be described. Thus, the present review will be expected to elucidate the possible mechanism of enzyme inactivation in relation to structure modification to provide a theoretical guide for further understanding the enzymatic caused browning mechanism. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.