Study on Effect of High Pressure Treatment of Fresh Pear Juice on PPO Activity

Objective To study the effect of high pressure alone or combined with heating treatment of fresh pear juice on PPO activity in it.Methods The ultrahigh pressure technology alone or combined with heating was used in the processing of fresh pear juice added VC or not,and then the color of juice and activity of PPO in it was assayed.Results As the pressure used increased,the activity of PPO in juice did not change significantly during the pressure scope of 200MPa￣600MPa and 400 MPa could activate PPO in juice.Effect of pressure on inactiva-tion of PPO became remarkable when pressured above 600 MPa.PPO in juice added VC was activated when pressured below 500 MPa and was inactivated when pressured above 600 MPa or combined with heating.The activity of PPO in juice decreased step by step with the increasing of heating temperature and pressure holding time.The treatment of 500 MPa above 60 ℃ or 750 MPa above 50 ℃ could inactivate PPO by 60% activity and the color change of juice was insignificant under the condition of 750 MPa above 50 ℃(△E was 0.9).Conclusion PPO in pear juice is hardly inactivated by high pressure.