Polyphenol Qxidase of Kiwifruit

Abstract

Polyphenol oxidase in kiwifruit (Actinidia chinensis planch) was extracted and purified through (NH 4 ) 2 SO 4 fractionation, dialysis and chromatography on DEAE‐cellulose column. Polyacrylamide disc‐gel electrophoresis showed eight bands with oxidase activity. The molecular weight of the dominant isozyme was 25,000 as determined by gel electrophoresis. The cresolase fraction appeared in the first peak (FA1P) and catecholase in the fourth peak (FA4P) when eluted from a DEAE‐cellulose column. The optimum pH of the FA4P fraction was 7.3. The Km value was 50 mM (+) catechin for FA1P and 8.7 mM for FA4P. Ascorbic acid delayed enzymic browning in kiwi fruit. The activation energy with (+) catechin as substrate was 4.0 Kcal/mole for FA1P and 7.0 Kcal/mole for FA4P.