Production of hydrolysates from unmilled AFEX-pretreated switchgrass and comparative fermentation with Zymomonas mobilis

Abstract The biological route for producing biofuel from lignocellulosic biomass involves many steps, including biomass harvesting and processing, pretreatment, enzymatic hydrolysis, microbial fermentation, and other downstream processes. Milling to reduce biomass fragment size is a common processing step, which aids subsequent biomass pretreatment and hydrolysis. However, milling also adds additional time and cost. We report here the production of 7% glucan loading hydrolysates using milled and unmilled Ammonia-Fiber Expansion (AFEX)-pretreated switchgrass (7% ASGH). No significant differences in fermentation performance by Zymomonas mobilis were observed between milled and unmilled switchgrass hydrolysates. We also produced a higher 10.5% glucan loading ASGH (10.5% ASGH) using unmilled pretreated switchgrass, and found that xylose fermentation by Z. mobilis was greatly inhibited in the 10.5% ASGH. The chemical compositions of hydrolysates from unmilled and milled switchgrass were analyzed and compared.