Polymerization of lignin fragments contained in a model effluent by polyphenoloxidases and horseradish peroxidase/hydrogen peroxide system

An effluent containing soluble lignin fragments was treated with potato-pol yphenoloxidases (PPO) or horseradish peroxidase/hydrogen peroxide system (H RP/H2O2). In both cases the reaction was evidenced by the information of a brown precipitate that was a consequence of the polymerization of lignin fr agments. The effect of reaction time, pH, and amount of soluble lignin per unit of enzyme activity on the insolubilization yield was evaluated for PPO -initiated reactions. For HRP-initiated reactions, the amount of H2O2 per u nit of enzyme activity was also evaluated. Mathematical models were calcula ted to predict the insolubilization yield as a function of the significant variables. Based on these models, the insolubilization reaction was optimiz ed and reached:maximal values of ca. 50% in both reaction systems. Higher i nsolubilization yields were not achieved. Chemical characterization of the soluble lignin fragments indicated that the insolubilization yield could no t be improved, because the lignin fragments had limited amounts df free phe nolic substructures available for the initial steps of the polymerization r eaction. (C) 2000 Elsevier Science Inc. All rights reserved.