Abstract: Dehulled kernels of two varieties of Euryale ferox Slisb, Zihua Suqian and Zihua Ciqian from respectively Suzhou and Hongze, Jiangsu province of China, were used as raw materials to prepare and characterize crude polyphnol oxidase (PPO) extract. The results showed that PPO enzymes from both verities of gordon euryale had the highest activity at 45 ℃ and pH 6.5. Ferric and ferrous ions were highly effective in promoting PPO activity. Calcium inhibited PPO activity at low concentrations, but not at high concentrations. Aluminum ion and copper ion at low concentrations activated PPO activity, while high levels of copper ions inhibited it. PPOs were inhibited by organic acids, like citric acid, oxalic acid, ascorbic acid, and ethylenediaminetetraacetic acid (EDTA), and the reductants sodium bisulfate and sodium thiosulfate.

Key words: Euryale ferox, polyphenol oxidase, inhibitor