M74 - Enhancement of sorghum hydrolysis by addition of amylases to an ionic liquid-based deconstruction process

Biomass pretreatment by ionic liquids followed by enzymatic hydrolysis with cellulases and hemicellulases is an effective method to deconstruct lignocellulosic biomass. However, the presence of significant levels of starch in feedstocks like sorghum may restrict the amount of fermentable sugars that can be released from all polysaccharides in the biomass. Simultaneous conversion of starch, cellulose and hemicellulose deconstruction processes involving ionic liquid in a one-pot configuration is particularly important because it aims at utilizing the conversion of all potential sugar components in the biomass. To address this, we explored the effects of the addition of amylases to ionic liquid-pretreated sorghum biomass at different solid loadings (15 wt.% and 20 wt.%) and process conditions and evaluated their impact on sugar yields. The results show that the combination of enzymatic cocktails containing cellulase, hemicellulase, alpha-amylase, and glucoamylase activities can result in glucose yields up to 4.2 times higher than without amylases, reaching 96% glucan conversion. By using mixtures of sorghum grain (high starch content) and stover (low starch content), we show that higher glucose yields can be obtained from biomass with a higher starch content but even samples containing only stover can benefit from amylase addition. This study demonstrates new possibilities for process intensification when using starch-containing feedstocks.