Abstract: The purpose of this study was to investigate the inhibitory effects of 4-hexylresorcinol (4-HR) and ascorbic acid (AA) on the activity of purified polyphenoloxidase (PPO) from Solenocera crassicornis. In addition, the inhibitory mechanism was elucidated through kinetic modelling with respect to the structures of the inhibitors. The results showed that both 4-HR and AA could significantly inhibit PPO activity with a half-maximal inhibitory concentration (IC50) of 0.072 and 2.02 mmol/L, respectively and provoke a lag period for the enzymatic reaction. Each of the two compounds exerted competitive inhibition on PPO activity. The kinetic analysis indicated that both 4-HR and AA could be combined with the di-copper binding active center of PPO. 4-HR could consume PPO continuously and effectively by forming a highly stable complex. In conclusion, both 4-HR and AA have been shown to be effective in controlling the enzymatic reaction rate of PPO, 4-HR being stronger than AA. This result provides theoretical support for the application of sulfur-free 4-HR-AA composite preservative in the catching and processing of shrimp.

Key words: Solenocera crassicornis, polyphenoloxidase (PPO), 4-hexylresorcinol (4-HR), ascorbic acid, kinetic analysis