Ligninases remove phenolic inhibitors and facilitate yeast growth in lignocellulosic hydrolysate

Abstract

Abstract Sugar-containing hydrolysates as byproducts of dissolving pulp production could be a source of alcohol production, but the presence of fermentation inhibitors hampers this utilization route. In the present study, nine types of phenolic inhibitors were found and their removal by ligninases gave satisfactory results. Laccase removed 73.1% of phenolic inhibitors and produced three new aromatic compounds, whereas the combination of laccase and lignin peroxidase (as a dual-enzyme treatment) resulted in a removal rate of 91.7% without new product formation. Xylose as the main sugar in the hydrolysate was retained with a 90% yield, regardless of the enzymatic treatment, which modified, however, the kinetics of yeast growth. Laccase improved cells’ maximum specific growth rate (vmax) from 0.115 to 0.154 and reduced the saturation constant (Ks) from 53.4 to 42.5, whereas the dual-enzyme system improved vmax to 0.206 and reduced Ks to 42.44. The greater vmax and the smaller Ks imply a better growth rate, and accordingly, the dual-enzyme system is better suited for removing phenolic inhibitors.