Chemical Groups and Structural Characterization of Brown-Rotted Pinus massoniana Lignin

Milled wood lignins (MWLs) were isolated from sound and naturally brown-rotted Pinus massoniana (decayed by brown-rot fungus Poria cocos) by Björkman and Lundquist techniques. Both lignins were characterized by FT-IR, UV, Citation 1 H NMR, GPC, ESR spectroscopy, and chemical analyses methods. The results indicated the brown-rotted lignin was higher in the total acidic group, carbonyl, carboxyl, and phenol hydroxyl contents, but lower in methoxyl content than sound lignin. The C9 formulas were calculated for sound and brown-rotted lignin as C9H8.78O2.85(OCH3)0.83 and C9H8.63O3.01(OCH3)0.71, respectively. Sound lignin had 0.75 aliphatic hydroxyl group and 0.17 phenolic hydroxyl group per C9-unit, and brown-rotted lignin had 0.62 aliphatic hydroxyl group and 0.30 phenolic hydroxyl group per C9-unit; lignins were mainly guaiacyl-type lignin, and β-O-4 structures constituted the main intermonomeric connections. Based on the analytical results and proposed reaction mechanism, demethylation, oxidation, and depolymerization were the most important modifications of lignin by brown-rotted fungi.