The effect of fungal decay ( Agaricus bisporus) on wheat straw lignin using pyrolysis–GC–MS in the presence of tetramethylammonium hydroxide (TMAH)

Abstract

Pyrolysis–gas chromatography–mass spectrometry, in the presence of tetramethylammonium hydroxide (TMAH), was used in the molecular characterisation of lignin in wheat straw during its fungal degradation by Agaricus bisporus. The decayed wheat straw had a lower proportion of syringyl to guaiacyl derived moieties than its native counterpart. The ratio of methyl 3,4-dimethoxybenzoate to 3,4-dimethoxybenzaldehyde increased from 1.0 in native wheat straw to 6.4 following fungal degradation. Similarly the ratio of methyl 3,4,5-trimethoxybenzoate to 3,4,5-trimethoxybenzaldehyde increased from 1.6 in native wheat straw to 3.1 upon decay. The increase in both guaiacyl and syringyl acid to aldehyde ratios indicated that A. bisporus induces oxidative cleavage of lignin at the CαCβ bonds. Both the threo- and erythro- isomers of 1-(3,4-dimethoxyphenyl)-1,2,3-trimethoxypropane decreased in intensity relative to other thermochemolysis products in degraded wheat straw. The increase in the ratio of methyl 3,4,-dimethoxybenzoate to the sum of 1-(3,4-dimethoxyphenyl)-1,2,3-trimethoxypropane ( threo- and erythro- isomers) from 1.0 in native wheat straw to 10.9 in A. bisporus decayed wheat straw confirmed that the fungus had cleaved alkyl side chains. Pyrolysis–gas chromatography–mass spectrometry in the presence of TMAH provides a sensitive method for tracking the oxidative degradation of lignin during the fungal decay of wheat straw.