Purification and some properties of polyphenol oxidase of longan fruit

Polyphenol oxidase (PPO) was isolated from longan (Dimocarpus longan Lour.) fruit peel, with a 46-fold purification of PPO by ammonium sulfate, Sephadex G-200 and Phenyl Sepharose being achieved. Pyrogallol, 4-methylcatechol, and catechol were good substrates for the enzyme, and activity with chlorogenic acid, p-cresol, resorcinol, or tyrosine was not observed. The optimal pH for PPO activity was 6.5 with 4-methylcatechol. The enzyme had a remarkably temperature optimum (35 degrees C) and was relatively stable, requiring a little more than 20 min at 50 degrees C for 50% loss of activity. Reduced glutathione, L-cysteine, thiourea, FeSO4 and SnCl2 markedly inhibited PPO activity, whereas MnSO4 and CaCl2 enhanced PPO activity. Data obtained in this study might help to better understand longan fruit peel browning. (C) 1999 Elsevier Science Ltd. All rights reserved.