(325a) Optimizing Pretreatment of Brown Midrib Maize Silage for Effective Fermentation at High Solids Loading

Both corn grain and grain stover have been examined and utilized as biofuel feedstocks. Maize silage (wet stored, partially fermented maize stover plus immature grain) is an alternative that combines starch and cellulosic processing in a single feedstock. The commercial brown midrib (BMR marketed by Mycogen, wholly owned subsidiary of Dow AgroSciences) has lowered expression of caffeic acid O-methyl transferase, a key enzyme in the biosynthesis of S monolignols. We carried out a compositional analysis for two commercial varieties of maize silage (regular and brown midrib) for starch, cellulose, hemicellulose, and lignin content. Our results show that for the commercial varieties, the lignin content (Klason lignin plus acid soluble lignin) is indistinguishable. However, the BMR silage exhibits significantly higher cellulose enzymatic digestibility. Liquid hot-water pretreatment was optimized for each silage variant. Optimal pretreatment conditions were similar between BMR and regular silage, which was less severe than required for dry stover from similar maize varieties. Simultaneous saccharifications and fermentations were subsequently performed on pretreated whole silage and ground silage at 25% (w/v) total solids using Celluclast 1.5L and Novozyme 188 and the glucose/xylose co-fermenting yeast S. cerevisiae 424A(LNH-ST). The results show that the improved cellulose hydrolysis performance of BMR silage compared to regular silage is also seen in pretreated material, resulting in significantly higher yields of ethanol after SSF.