CHEMICAL CHARACTERIZATION BY PYROLYSIS-GAS CHROMATOGRAPHY MASS-SPECTROMETRY OF ACID-PRECIPITABLE POLYMERIC LIGNIN (APPL) FROM WHEAT-STRAW TRANSFORMED BY SELECTED STREPTOMYCES STRAINS

The possible differential biodegradation of wheat straw performed by d ifferent Streptomyces strains was investigated on solid-state fermenta tion conditions. The modified lignin polymer named acid-precipitable p olymeric lignin (APPL), harvested with NaOH or water, from wheat straw transformed by selected Streptomyces strains was tentatively characte rized by pyrolysis-gas chromatography-mass spectrometry (PY/GC/MS). Fo r comparative analyzes, lignin-carbohydrate-protein complexes obtained from uninoculated wheat straw were used as controls. Significant diff erences in the p-hydroxyphenyl: guaiacyl : syringyl (H: G: S) and in t he syringyl/guaiacyl (S/G) ratios of the APPLs extracted with water fr om wheat straw transformed by the strains Streptomyces UAH 23, Strepto myces 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 S-lignin units, a decrease in the condensed G-un its was produced by S. UAH 52 and S. viridosporus T7 A. From the resul ts obtained it can be concluded that PY/GC/MS is a suitable technique to establish differences in the composition of the main product of sol ubilization of lignocellulose by different Streptomyces strains. Never theless for chemical characterization of this polymer, it is important to select the method to be used to extract the APPL from degraded res idues in order to prevent chemical modifications of the substrate as o ccurred when NaOH was used which make difficult to attribute the chang es observed to the microbial activity.