Chemical characterization by pyrolysis/gas chromatography/mass spectrometry of acid-precipitable polymeric lignin (APPL) from wheat straw transformed by selected streptomyces strains

Abstract

The possible differential biodegradation of wheat straw performed by different Streptomyces strains was investigated on solid-state fermentation conditions. The modified lignin polymer named acid-precipitable polymeric lignin (APPL), harvested with NaOH or water, from wheat straw transformed by selected Streptomyces strains was tentatively characterized by pyrolysis-gas chromatography-mass spectrometry (PY/GC/MS). For comparative analyzes, lignin-carbohydrate-protein complexes obtained from uninoculated wheat straw were used as controls. Significant differences in the p-hydroxyphenyl: guaiacyl: syringyl(H: G: S) and in the syringyl guaiacyl ( S G ) ratios of the APPLs extracted with water from wheat straw transformed by the strains Streptomyces UAH 23, Streptomyces UAH 52 and Streptomyces viridosporus T7 A were detected compared with the control. While S. UAH 23 produced a preferential degradation of the non-condensed Slignin units, a decrease in the condensed G-units was produced by S. UAH 52 and S. viridosporus T7 A. From the results obtained it can be concluded that PY/GC/MS is a suitable technique to establish differences in the composition of the main product of solubilization of lignocellulose by different Streptomyces strains. Nevertheless for chemical characterization of this polymer, it is important to select the method to be used to extract the APPL from degraded residues in order to prevent chemical modifications of the substrate as occurred when NaOH was used which make difficult to attribute the changes observed to the microbial activity.