ESR Study in Reactive Oxygen Species Free Radical Production of Pinus kesiya var. langbinensis Heartwood Treated with Laccase

Enzymatic oxidation of lignin phenolic hydroxyl groups can enhance the level of autoadhesion between wood fibers or particles depending upon the bonding mechanism of wood-based materials without synthetic adhesives such as urea and phenol formaldehyde. The adhesive effect is caused by an increased number of reactive oxygen groups at the fiber surface. The parameters of laccase-treated wood fibers play vital roles in generating reactive oxygen species (ROS) free radicals. Laccase I (white-rot fungi) and laccase II (Aspergillus sp.) are used to catalyze the oxidation of heartwood powder of Pinus kesiya var. langbianensis in suspension under different pH, values, temperatures, treatment times and different laccase concentrations. Electron spin resonance spectroscopy and spin trapping technique were used to detect the ROS free radicals generated in the laccase-treated heartwood powder and it was found that in it the concentrations of ROS free radicals was higher than that in the control. Analysis of variance indicates that there was significant difference between the ROS concentration values of laccase-treated heartwood powder under different pH values, treatment temperatures and times, and laccase dosages for both laccase I and II. Furthermore, the concentration of ROS free radicals generated by laccase I is higher than that generated by laccase II. It was found that the optimum conditions for generation of ROS in laccase-treated heartwood powder by the two kinds of laccase are pH 3.0; treatment temperature 50 degrees C; treatment time, 2 h; enzyme concentration, 20 units/g of wood powder.