Optimization of Cellulase Complexes for the Enhanced Enzymatic Digestibility of Hydrothermally Pretreated Empty Fruit Bunches

Enzymatic hydrolysis is considered important in biomass-sugar conversion process. The enzymatic digestibility using current commercial cellulases varies depending on biomass types and pretreatment methods. In this study, the optimization of cellulase complexes for hydrothermally pretreated empty fruit bunches (EFB) was performed by supplementing accessory enzymes and chemicals. Hydrothermal pretreatment was conducted at 190°C for 15 min at solid to liquid ratio of 1:1 (w/w) using 10-L scale reactor. After 72 h saccharification of pretreated EFB, 50.0% of theoretical glucose yield was achieved with 10 FPU Cellic CTec2/g glucan. The effects of xylanase, β-glucosidase and polyethylene glycol (PEG) on enzymatic digestibility were also investigated. By the single factor supplement of these three accessory agents, the glucose yield increased from 50.0% up to 64.6%. The optimal concentrations of the three accessory agents were determined as 67.5 mg, 6.0 mg and 62.5 mg/g of glucan, respectively. Finally, combined effects of accessary enzymes and PEG were investigated by varying glucan loadings, and 79.3% of the maximal glucose yield was obtained. Notably, the increased digestibility due to the combined effect was much more significant at higher glucan loadings (e.g., 71.9% and 32.0% of glucose yield with and without supplementation at 12% glucan loading, respectively). Therefore, this study contributes to designing cellulase complexes to increase the digestibility of hydrothermally pretreated biomass at high solids loading.