KINETICS OF WHEAT STRAW SOLID-STATE FERMENTATION WITH TRAMETES-VERSICOLOR AND PLEUROTUS-OSTREATUS - LIGNIN AND POLYSACCHARIDE ALTERATION AND PRODUCTION OF RELATED ENZYMATIC-ACTIVITIES

The kinetics of straw solid-state fermentation (SSF) with Trametes versicolor and Pleurotus ostreatus was investigated to characterize the delignification processes by these white-rot fungi. Two successive phases could be defined during straw transformation, characterized by changes in respiratory activity, changes in lignin and polysaccharide content and composition, increase in in-vitro digestibility, and enzymatic activities produced by the fungi. Lignin composition was analysed after CuO alkaline degradation, and decreases in syringyl/guaiacyl and syringyl/p-hydroxyphenyl ratios and cinnamic acid content were observed during the fungal treatment. An increase in the phenolic acid yield, revealing fungal degradation of side-chains in lignin, was produced by P. ostreatus. The highest xylanase level was produced by P. ostreatus, and exocellulase activity was nearly absent from straw treated with this fungus. Laccase activity was found in straw treated with both fungi, but lignin peroxidase was only detected during the initial phase of straw transformation with T versicolor. High levels of H2O2-producing aryl-alcohol oxidase occurred throughout the straw SSF with P. ostreatus.