Polyphenol oxidase (PPO) was isolated from Victoria grapes (Vitis vinifera ssp. Sativa) grown in South Africa and its biochemical characteristics were studied. Optimum pH and temperature for grape PPO activity were pH 5.0 and T = 25 degrees C with 10 mM catechol in McIlvaine buffer as substrate. PPO showed activity using the following substances: catechol, 4 methyl catechol, (D), (L)-DOPA, (+) catechin and chlorogenic acid. K-m and V-max values were 52.6 +/- 0.00436 mM and 653 +/- 24.0 OD400 nm/min in the case of 10 mM catechol as a substrate. Eight inhibitors were tested in this study and the most effective inhibitors were found to be ascorbic acid, L-cysteine and sodium metabisulfite. Kinetic studies showed that the thermal inactivation of Victoria grape PPO followed first-order kinetics, with an activation energy, E-a = 225 +/- 13.5 of U/mol. Both in semipurified extract and in grape juice, PPO showed a pronounced high pressure stability. (c) 2004 Elsevier Ltd. All rights reserved.