Enzymatic hydrolysis of thermochemically pretreated biomass using a mixture of cellulolytic enzymes produced from different fungal sources

Enzymatic hydrolysis of pretreated lignocellulosic raw material is one of the major steps in the biofuel production. In this study, sorghum straw was pretreated under previously optimized conditions (using 0.5 M sodium hydroxide, 8% substrate concentration, 120 °C temperature and 20 min of incubation time). Cellulase enzymes were produced using three different fungal sources (Aspergillus niger, Fusarium oxysporum and Trichoderma harzianum). Enzymatic hydrolysis of pretreated biomass was carried out using individual and different mixture of cellulases. Maximum reducing sugar yield was obtained when an equal mixture of three different cellulases was used. The enzymatic hydrolysis process was optimized through central composite design based on response surface methodology using an equal mixture of three different cellulases (1:1:1). The data showed that maximum reducing sugar yield of 464.2 mg/g dry substrate was obtained at 10% substrate concentration, 55 °C and after 48 h of incubation. Further, batch (a process where all the substrates were fed into the bioreactor at the beginning of the reaction) and fed-batch (a process where substrates were fed into the bioreactor at specific time intervals) process of enzymatic hydrolysis were compared at high substrate concentration (20%). The results showed that an increase in reducing sugar yield (355.6 mg/g dry substrate) was obtained in case of fed-batch enzymatic hydrolysis as compared to batch enzymatic hydrolysis (285.3 mg/g dry substrate) process. The above results can be useful for efficient hydrolysis of lignocellulosic biomass and cost-effective biofuel production.