DETOXIFICATION OF WOOD HYDROLYSATES WITH LACCASE AND PEROXIDASE FROM THE WHITE-ROT FUNGUS TRAMETES-VERSICOLOR

Fermentation of wood hydrolysates to desirable products, such as fuel ethanol, is made difficult by the presence of inhibitory compounds in the hydrolysates. Here we present a novel method to increase the ferme ntability of lignocellulosic hydrolysates: enzymatic detoxification. B esides the detoxification effect, treatment with purified enzymes prov ides a new way to identify inhibitors by assaying the effect of enzyma tic attack on specific compounds in the hydrolysate. Laccase, a phenol oxidase, and lignin peroxidase purified from the ligninolytic basidio mycete fungus Trametes versicolor were studied using a lignocellulosic hydrolysate from willow pretreated with steam and SO2. Saccharomyces cerevisiae was employed for ethanolic fermentation of the hydrolysates . The results show more rapid consumption of glucose and increased eth anol productivity for samples treated with laccase. Treatment of the h ydrolysate with lignin peroxidase also resulted in improved fermentabi lity. Analyses by GC-MS indicated that the mechanism of laccase detoxi fication involves removal of monoaromatic phenolic compounds present i n the hydrolysate. The results support the suggestion that phenolic co mpounds are important inhibitors of the fermentation process.