| Sumario: | Lignin biodegradation is an oxidative process involving the action of fungal enzymes and the subsequent chemical reactions of aromatic radicals formed. Aromatic acid release has been reported during biodegradation of lignocellulosic materials, suggesting oxidative degradation of side chains in lignin units. In the present study, wheat lignin degradation by two basidiomycetes was investigated by pyrolysis coupled to GC/MS after sample permethylation. In this way, analysis of phenolic and etherified lignin units, yielding C4-OMe and C4-OH compounds respectively, was performed. The amount of etherified residues of carboxy-free vanillic and syringic acids was found to be very low in sound straw. However, the molar abundances of these acid residues increased strongly during fungal degradation of lignin. For example, each of them attained 8% of total lignin-derived compounds recovered after pyrolysis of straw treated with Pleurotus eryngii (after 50% lignin degradation). These findings support Ca-Cß cleavage as one of the most frequent reactions during lignin biodegradation, and constitute evidence for in situ cleavage of lignin side chains during fungal attack to this macromolecule.
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