Abstract:

The kinetic parameters Km and vmax/Km of polyphenol oxidase (PPO) from three Franco-American hybrid grape
varieties namely “Guankou”, “Goldfinger”, “Huangmi” and two Vitis vinifera varieties i.e., Zexiang and seedless white
were compared towards different substrates: catechol, 4-methylcatechol, catechin and caffeic acid as well as optimal pH
and temperature, thermal stability, and the effect of inhibitors on PPO activity. Results showed that the affinity of PPO
from five varieties grapes for catechol was significantly different, whereas no significant difference was observed when
4-methylcatechol, catechin and caffeic acid were used as substrates. The catalytic efficiency of PPO from Franco-American
hybrid grapes and Vitis vinifera for catechol was significantly different while no significant difference was observed when
4-methylcatechol, catechin and caffeic acid were used as substrates. The catalytic efficiency of PPO from “Guankou”
grapes for catechin and caffeic acid was obviously higher than that of four other varieties of grapes. Among inhibitors
tested, ascorbic acid and sodium metabisulfite had stronger inhibition on PPO from all five varieties. The inhibitory effect of
sodium metabisulfite on PPO from “Guankou” grapes was weaker than on PPO from four other varieties. Optimal pH and
temperature of PPO from five varieties of grapes had no significant difference.

Key words: polyphenol oxidase, kinetic parameters, catalytic efficiency, inhibition