1.3 Overview

Theoretically, the basic process for biochemical conversion of lignocellulosic biomass into ethanol or other biofuels is relatively straightforward. First, the lig — nocellulosic matrix must be treated to gain access to and/or separate the main components: lignin, cellulose, hemicellulose, and pectin. The polysaccharides (cel­lulose and hemicelluloses) are then hydrolyzed to sugars, which are fermented to ethanol. This hydrolytic conversion process for lignocellulosic biomass contributes to the technical barriers that currently limit commercial operations. The fermen­tation process for ethanol production from lignocellulosic biomass is also more complex than for corn-based ethanol production. Hydrolysates of lignocellulosic biomass typically contain significant amounts of pentoses (e. g. xylose and arabi — nose). These C5 sugars are not readily fermented to ethanol by the commonly-used yeast (Saccharomyces cerevisiae). Efficiently converting both glucose and pentoses (xylose and arabinose) into ethanol or other biofuels and at reasonably high con­centrations (8-12%) is another challenge for the fermentation microorganisms.