Study on Enzymatic Characterization of Pyphenol Oxidase of Pear Fruit

Polyphenol oxidase(PPO) was the key enzyme of enzymatic browning,and was closely related to the color and antioxidant capacity of processed fruit and vegetable products.The enzymatic characterization of PPO from pears were studied in this paper with spectrophotometry method and based on substrate of catechol.The results showed that,both of pH and temperature had a significant effect on the activity of PPO of pear,the PPO had an optimum pH at 4.5 and optimum temperature at 34 ℃.In the process,the PPO activity of pear could be decreased by the regulation of pH and temperature to reduce the browning.The kinetics of the enzyme-catalyzed reaction of PPO was established and was in accord with Michaelis-Menten equation,and R2was 0.997 2.The Km,Vmax and kinetic equation were respectively 0.36 mol·L-1,2.09 U·min-1and1 V =0.173 71 [S] +0.477 5,using catechol as substrate.The PPO possessed certain thermal stability,furthermore,the higher the heating temperature was,the shorter time inhibiting PPO activity needed.It could effectively inhibit the enzymatic browning reactions under 90 ℃ for 1 min.This approach avoided the loss of nutrition and was closer to natural color in fresh pear juice.