DEMONSTRATION OF IN-SITU OXIDATIVE-DEGRADATION OF LIGNIN SIDE-CHAINS BY 2 WHITE-ROT FUNGI USING ANALYTICAL PYROLYSIS OF METHYLATED WHEAT-STRAW

Lignin biodegradation is an oxidative process involving the action of fungal enzymes and the subsequent chemical reactions of aromatic radic als formed. Aromatic acid release has been reported during biodegradat ion of lignocellulosic materials, suggesting oxidative degradation of side chains in lignin units. In the present study, wheat lignin degrad ation by two basidiomycetes was investigated by pyrolysis coupled to G C/MS after sample permethylation. In this way, analysis of phenolic an d etherified lignin units, yielding C4-OMe and C4-OH compounds respect ively, was performed, The amount of etherified residues of carboxy-fre e vanillic and syringic acids was found to be very low in sound straw. However, the molar abundances of these acid residues increased strong ly during fungal degradation of lignin. For example, each of them atta ined 8% of total lignin-derived compounds recovered after pyrolysis of straw treated with Pleurotus eryngii (after 50% lignin degradation). These findings support C-alpha-C-beta cleavage as one of the most freq uent reactions during lignin biodegradation, and constitute evidence f or in situ cleavage of lignin side chains during fungal attack to this macromolecule. (C) 1997 by John Wiley & Sons, Ltd.