INHIBITORY EFFECT OF KOJIC ACID ON SOME PLANT AND CRUSTACEAN POLYPHENOL OXIDASES

Kojic acid exhibited a competitive inhibition for the oxidation of chlorogenic acid and catechol by potato polyphenol oxidase (PPO) and of 4-methylcatechol and chlorogenic acid by apple PPO. This compound showed a mixed-type inhibition for white shrimp, grass prawn, and lobster PPO when DL-beta-3,4-dihydroxyphenylalanine (DL-Dopa) and catechol were used as substrates but a mixed-type and a competitive inhibition for mushroom PPO when DL-Dopa and L-tyrosine were used, respectively. Potato and apple PPOs were shown to have much higher affinities for Dopa than for chlorogenic acid, 4-methylcatechol, and catechol. These two PPOs also had a higher affinity for Dopa than the other four PPOs. Kojic acid is thus an effective inhibitor of PPO on the oxidation of Dopa.