Studies on Effect of Ultrahigh Pressure Treatment on PPO Activity in Fresh Apple Juice

The ultrahigh pressure technology alone or combined with heating was used in processing fresh apple juice and the its effect on PPO activity in juice was studied.As the pressure increased,the activity of PPO in juice reduced slowly during the pressure scope of 200MPa～500MPa and the effect of pressure on activity was lest when the pressure was 300 MPa.Effect of pressure on inactivation of PPO became remarkable when pressured above 600 MPa.PPO was activated by adding VC into juice when pressured below 500 MPa and was inactivated when pressured above 600 MPa or combined with heating.The activity of PPO in juice decreased as the increasing of heating temperature and pressure holding time.The treatment of 400MPa above 50℃ could inactivate PPO activity by 60% and 750 MPa above 50℃ could inactivate more than 90% activity,the color change of juice(△E) was 0.6.