Biotransformation of phenols using immobilised polyphenol oxidase

Polyphenol oxidase (PPO), obtained from Agaricus bisporus, can be used in hydroxylating a range of phenolic substrates to yield catechols which are then oxidised by the enzyme to give o-quinone products. The objective of this study was to develop systems whereby phenols could be transformed by PPO, and the products of the biotransformation could be isolated and characterised. By comparing the product mixtures obtained using soluble PPO and various forms of immobilised PPO, in aqueous and non-aqueous media, we have found significant differences in reaction rates and in the proportions of catechol and quinone produced. PPO in solution is inactivated by the reaction products, but when it is immobilised, the separation of products from the enzyme reduces this inhibition. Immobilisation also leads to increased stability, and allows continuous use of the enzyme. In bioreactors containing customised novel asymmetric capillary membranes as the enzyme support, high concentrations of phenolic substrates were converted. The addition of a chitosan-containing column downstream from the capillary membrane bioreactor facilitated the removal of the coloured quinone products from the permeate, and recycling of the substrate solution. (C) 1998 Elsevier Science B.V. All rights reserved.