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.