Hinokitiol Inhibits Polyphenol Oxidase and Enzymatic Browning

We screened for inhibitors of enzymatic browning among fermented broths of lactic acid bacteria (58 strains), extracts of spices (7 samples), and food additives (34 samples) from the standpoint of practical use. We found that hinokitiol, a preservative, definitely inhibited the browning of apple sections. An apple section sprayed with a 0.02% hinokitiol solution did not turn brown for 2 h at room temperature. Hinokitiol competitively inhibited apple polyphenol oxidase (PPO). The Ki value of hinokitiol against apple PPO was 5.5 mu M, while the Km value of chlorogenic acid was 2.5 mM. Furthermore hinokitiol non-competitively inhibited tyrosinase and the discoloration of shrimp caused by tyrosinase during cold storage.