Lignin Changes after Steam Explosion and Laccase-Mediator Treatment of Eucalyptus Wood Chips

Eucalyptus globulus chips were steam exploded followed by treatment with a laccase-mediator system (LMS) under different experimental conditions. Removal of hemicelluloses and, to a lesser extent, lignin was observed. Thermogravimetic analyses of whole meal obtained from chips before and after steam explosion indicated an increase in lignin degradation temperature due to lignin condensation. In contrast, application of LMS treatment caused a reduction in lignin and polysaccharide degradation temperatures. Lignins were isolated from wood samples before and after each treatment and analyzed by 2D NMR and C-13 NMR. An increase in carboxyl and phenolic hydroxyl groups and a significant decrease in beta-O-4 structures were found in steam-exploded samples. The most relevant changes observed after laccase treatment were increased secondary OH and degree of condensation.