Effect of High Pressure (HP) Treatments on Polyphenoloxidase (PPO) Activity in Pear Juices

The effect of high hydrostatic pressure treatment (0.1~500 MPa) combined with mild heat treatment (20~60 ℃) under different pH values (3.0~7.0) on polyphenoloxidase (PPO) activity of Chinese Dangshan pear juice was investigated in this paper. Results showed that the polyphenoloxidase was activated when the high pressure treatment on the pear juice was carried out under the temperature 50 ℃, the dwell time 10 min, the pH5 and the pressure between 200~300 MPa. The polyphenoloxidase activity reached the maximal level under temperature of 30 ℃ synergizing high pressure treatment, and decreased under the temperature of above 30 ℃. The polyphenoloxidase residual activity was rapidly decreased with the increasing of dwell time. The polyphenoloxidase residual activity and the pressureresistance reached their maximal level under pH6.