Abstract: Green tea powder was used as the substrate to investigate the effects of seven metal ions including Cu2+, Mn2+, Mg2+, Ca2+, Na+, Al3+ and Fe3+ on the activity of polyphenol oxidase (PPO) extracted from homogenized eggplant fruit. Cu2+, Mn2+ and Mg2+ were found to be able to promote the activity of the enzyme, while the other four metal ions had an inhibitory effect on the enzyme. The enzyme was activated by 3 mmol/L Cu2+, resulting in a total theaflavins content of 7.45 mg. Fe3+ at 5 mmol/L dramatically inhibited the enzyme and as a result, the total theaflavins content was decreased to 0.26 mg.

Key words: polyphenol oxidase (PPO), metal ion, promoting effect, inhibitory effect, inhibitor