Enzymatic hydrolysis of steam-pretreated sweet sorghum bagasse by combinations of cellulase and endo-xylanase

Sweet sorghum bagasse (SSB) is considered a potential lignocellulosic raw material for the production of fuel ethanol by means of pretreatment, enzymatic hydrolysis and fermentation. Enzyme cocktail composition is critical to achieve maximum sugar yield per gram of enzyme used. Given that the enzyme composition relies on feedstock properties and pretreatment applied, the main objective of this study was to develop an optimised combination of cellulase (Cellic® CTec2) and endo-xylanase (Cellic® HTec2) enzyme preparations (cocktail) that is adapted to steam treated sorghum bagasse. This was done by using a central composite design by which combined effects of Cellic® CTec2 and Cellic® HTec2 were investigated further using response surface methodology (RSM). The optimum was defined as the minimum total enzyme dosage that is needed for a target glucan conversion of at least 80% for an incubation period of 72 h. The addition of Cellic® HTec2 proved to boost the glucan conversion to glucose by Cellic® CTec2, but synergistic interaction was only observed at early stages of the enzymatic hydrolysis and mainly for those combinations with lower cellulase content. The pretreatment and enzymatic hydrolysis with 0.15 mL/g WIS (water insoluble solids) of Cellic® CTec2 (24.9 mg protein/g WIS) and 0.32 mL/g WIS of Cellic® HTec2 (54 mg protein/g WIS), respectively, resulted in 364.8 kg sugar/ton of bagasse, 20% more than with a conventional enzyme combination.