Abstract: This paper studied the characteristics and inhibition of polyphenoloxidase(PPO) in Opuntia dillenii. The resultsshowed: the optimum temperature of PPO was 50℃ and the optimum pHs were 4.0 and 7.0 respectively, so as to display thatthere were two isoenzymes. All citric acid, ascorbic acid and ethylene diamine tetraacetic acid(EDTA) had certain inhibitoryeffects., Their inhibiting capability to the PPO was in the order as follows: citric acid>ascorbic acid>EDTA. It had inhibitoryeffect on the PPO that EDTA mainly chelated the Cu2+ as co-enzyme factory of PPO. The chelating ability of ascorbic acid toCu2+ was weaker than EDTA, but the reducing ability of ascorbic acid was stronger than EDTA, while citric acid inhibited thePPO through both reducing pH and chelating Cu2+.

Key words:  Opuntia dillenii, polyphenoloxidase, characteristics, inhibiting mechanism