Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Four differentially pretreated corn stovers (PCS) were subjected to enzymatic digestion at various solids and enzyme loadings. PCS was prepared from milled Kramer corn stover using a 2% Sulfuric acid treatment at 158oC for 5 minutes (base pretreatment). Three additional PCS substrates were prepared with the following modifications to the base pretreatment: deacetylated (DAc; 0.1M NaOH, 80C 2 hr prior to pretreatment), oligomer hold (OH; 7.5 mg Sulfuric Acid/g dry biomass, 130 C, 20 min after pretreatment), and Deacetylation + Oligomer hold (DAc + OH). These substrates were incubated for 5 days at 50 oC using a 10:1 mixture of Cellic Ctec2 : Htec2 (Novozymes) at enzyme loadings ranging from 15 mg to 60 mg per gram of glucan and at total solids loadings ranging from 15 to 30% (w/w). The results indicate that much of the decrease in conversion typically seen with increasing solids loadings is relieved by diafiltering the commercial enzyme preparations to remove low molecular weight components (>5000 Da), and that PCS which was subjected to both deacetylation and the oligomer hold step gave highest overall levels of glucan and xylan conversion. Saccharification of all substrates resulted in significant amounts of cellobiose accumulation. Interestingly, supplementation with beta glucosidase can eliminate accumulation of cellobiose but does not improve conversion levels to target levels (>85%), suggesting further barriers such as glucose or oligomers other than cellobiose are inhibiting enzyme hydrolysis. Future work will aim to elucidate these remaining specific barriers to achieving higher conversion levels during high solids saccharifications.