2.6 Enzyme hydrolysis
The productivity of fermentable sugars from wild-type (WT) and transgenic (TG) sorghum stover before and after pretreatments were evaluated by enzymatic digestibility assays. Enzymatic hydrolysis and enzyme activity analysis were conducted in accordance with the NREL procedure.30,31 The enzyme activity of Cellic CTec 2 was measured to be 137 FPU/ml. Enzymatic hydrolysis of untreated and pretreated biomass was operated in an incubator at 50 °C with 180 rpm for 72 h. Wet samples equivalent to 200 mg of dry weight were loaded into a 100 ml Erlenmeyer flask with a rubber cap at a solid loading of 1 wt% in 50 mM sodium acetate buffer at pH 5.0 with 0.02% sodium azide. The Cellic CTec 2 was loaded at 20 FPU/g-biomass. The hydrolysis reaction was quenched by heating at 95 °C for 6 minutes in a heating block. The hydrolysate was centrifuged at 14,000 rpm for 0.3 h followed by filtering through a 0.22 μm nylon filter prior to the HPLC analysis. All enzymatic hydrolysis was conducted in duplicates.