Unfolding and Inhibition of Polyphenoloxidase Induced by Acidic pH and Mild Thermal Treatment

Abstract

The activity of polyphenoloxidase (PPO) treated by acidic pH and mild thermal processing was found to be closely related to the conformational changes. Weakly acidic environment (pH 4.0–6.0) resulted in reversible inhibition of activity and slight changes in the conformation, and refolding of PPO was observed after readjusting pH to 6.8. At pH lower than 4.0, PPO activity was strongly inhibited with great unfolding in conformation and all changes were irreversible. Acidic environment increased the susceptibility of PPO to thermal treatment, and greater changes in activity and conformation of PPO were observed under the combined treatment of acidic pH and mild thermal treatment. Besides, the inactivation of PPO induced by thermal treatment followed a biphasic kinetic model, and acidic pH increased the inactivation rate of labile and stable PPO. The combination of acidic pH and mild thermal processing expected to avoid the nutritional loss and sensory damage in fruits and vegetables caused by severe acid or temperature.