The early oxidative biodegradation steps of residual kraft lignin models with laccase

A number of model compounds resembling the fundamental bonding patterns of residual kraft lignin, including a series of stilbenes, were incubated with laccase from Trametes versicolor in the presence and absence of delignific ation 'mediators' ABTS and HBT. The condensed kraft lignin model compounds seem to undergo initial degradation by laccase mainly via benzylic oxidatio n, demethylation and hydroxylation reactions. Phenolic 5-5', diphenylmethan e and alpha-5 lignin models were found to be degraded mainly via side-chain oxidation reactions. Among the models studied, a phenolic stilbene was fou nd to be the most reactive, yielding several products showing side-chain ox idation/transposition, demethoxylation and hydroxylation reactions. Non-phe nolic 5-5', diphenylmethane and stilbene model compounds were found unreact ive even in the presence of the laccase-mediator system. (C) 1998 Elsevier Science Ltd. All rights reserved.