PYROLYSIS GAS-CHROMATOGRAPHY MASS-SPECTROMETRY OF MILLED WOOD LIGNIN OF 2 CHILEAN WOODS NATURALLY DECAYED BY GANODERMA-AUSTRALE, PHLEBIA-CHRYSOCREA AND A BROWN-ROT FUNGUS

Two native Chilean woods (Eucryphia cordifolia Cav, and Laurelia philippiana Looser) and their corresponding sound and degraded milled wood lignin preparations, were characterized by pyrolysis-gas chromatography/mass spectrometry. The main goal of this work was to study the chemical changes in a lignin molecule during the natural fungal decay. A higher proportion of syringyl (S) than guaiacyl (G) units was detected in the native wood of E. cordifolia (S/G ratio of 3.9), whereas L. philippiana native wood showed similar amounts of S and G units (S/G ratio of 0.9). The modified Bjorkman method used here proved to be a suitable procedure for removing almost all the carbohydrate fraction of wood, with only minor modifications (demethylations) to the resulting purified lignin. The alterations affecting the propane chain of lignin units (C-3-alkyl chain oxidations and shortenings) observed in L, philippiana after Phlebia chrysocrea (Berk. and Curt.) decay were similar to these described in E. cordifolia by Ganoderma australe (Fr.), except that the former were only detected in S-lignin units. Additionally, in L. philippiana some demethylation reactions were also suggested, although oxidations were not observed in the C-beta-position. Both fungi produced a decrease in lignin content, independent of the different S/G ratio of the studied woods. After the brown-rot fungus attack the lignin content did not change. Although this brown-rot microorganism does not substantially degrade lignin, it is able to produce some minor chemical alterations: demethylations and oxidations of lignin side-chains.