Oxidative polymerisation of phenols by a phenol oxidase from green olives

The phenol oxidase activity of green olive drupae was characterised in view of possible applications for the de-phenolisation of polluted waters. For experimental convenience, activity measurements were performed on acetone powders and raw-extracts from drupae tissues. Phenols were oxidised in the presence of dissolved molecular oxygen. Oxidation products were o-quinones undergoing non-enzymatic polymerisation. Final products were insoluble polymers that could be easily removed from the reaction mixture by centrifugation. The kinetics of activity loss was analysed and a possible "suicide substrate" deactivation mechanism, analogous to that of mushroom tyrosinase, has been proposed. Substrate specificity was particularly high towards o-diphenols and p-methyl substituted phenols. For real applications, the observed, low operational stability discourages the use of purified and immobilised enzyme in lieu of minced tissues. Furthermore, the seasonal availability of olive suggests an on-site use for polyphenol removal from vegetation waters resulting from the milling process.