Enhanced Enzyme Saccharification of Cereal Crop Residues using Dilute Alkali Pretreatment

Abstract

Mild alkali pretreatment of lignocellulosic biomass is an effective pretreatment method which improves enzymatic saccharification. Alkaline pretreatment successfully delignifies biomass by disrupting the ester bonds cross-linking lignin and xylan, resulting in cellulose and hemicellulose enriched fractions. Here we report the use of dilute alkaline (NaOH) pretreatment followed by enzyme saccharification of cereal crop residues for their potential to serve as feedstock in the production of next-gen biofuels in Australia. Specifically, we discuss the impacts of varying pretreatment parameters on enzymatic digestion of residual solid materials. Following pretreatment, both solids and lignin content were found to be inversely proportional to the severity of the pretreatment process. Higher temperatures and alkali strength were also shown to be quintessential for maximising sugar recoveries from enzyme saccharifications. Essentially, pretreatment at elevated temperatures led to highly digestible material enriched in both cellulose and hemicellulose fractions. Increasing cellulase loadings and tailoring enzyme activities with additional β-glucosidases and xylanases delivered greater rates of monosaccharide sugar release and yields during saccharification. Sugar conversion efficiency of alkali treated sorghum and wheat straw residues following enzyme saccharification, approached 80 and 85%, respectively. Considering their abundance and apparent ease of conversion with high sugar yield, cereal crop residues are ideally suited for the production of second generation biofuels and/or use as feedstock for future biorefineries.