OXIDATIVE-DEGRADATION OF ALKALI WHEAT-STRAW LIGNIN BY FUNGAL LIGNIN PEROXIDASE, MANGANESE PEROXIDASE AND LACCASE - A COMPARATIVE-STUDY

Lignin peroxidase (LiP), manganese peroxidase (MnP) from Phanerochaete chrysosporium and laccase from Pleurotus eryngii were separately used to degrade alkali wheat straw lignin (AL). In order to characterize t he catalytic action of the different enzymes, the chemical structure a nd the hydrodynamic properties of treated lignin were analyzed by thio acidolysis-gas chromatography and molecular size exclusion chromatogra phy. The results confirmed that only LiP was able to degrade guaiacyl (G) and syringyl (S) structures in non-phenolic methylated lignins. Ho wever, Provided that some phenolic terminal structures are present, Mn P and laccase were able to degrade the non-phenolic part of the polyme r linked by beta-O-4 alkyl aryl ether bonds. This suggested that the o xidative reactions catalyzed in alkali straw lignin could progress thr ough bond cleavages generating phenoxy radicals. The molecular size di stribution of both thioacidolysis products and the oxidized polymer sh owed that AL underwent condensation side-reactions regardless of the e nzymic treatment, but only UP oxidation led to the increase in the hyd rodynamic volume of the recovered lignin. This indicated that modifica tion by enzymes of bonding patterns in lignin is not always associated with alterations in the spatial network of the polymer.