Synergistic Effect of Ultrasonic and Fungal Pretreatment on Enzymatic Saccharification of Switchgrass

Biological pretreatment of cellulosic biomass is preferred to conventional methods because it is environmentally friendly. However, low pretreatment efficiency and long residence time associated with biological pretreatment limit its commercialization. The current study assessed the effect of ultrasonication and its combination with solid-state fermentation using an engineered mutant strain of the white rot fungus, T. versicolor (Tv m4D), on the enzymatic digestibility of switchgrass. Response surface approach featuring a four-factor, three-level Box Behnken experimental design was used to determine the optimum ultrasonic pretreatment conditions in terms of cellulose and hemicellulose composition and total solid recovery (TSR) of switchgrass. Ultrasonic pretreatment altered the holocellulose composition of switchgrass and resulted in biomass loss. The highest holocellulose degradation and material loss were obtained at acoustic power of 180 W. The effect of ultrasonication on the efficiency of enzymatic hydrolysis was minimal compared to fungal pretreatment. Ultrasonic-assisted enzymatic saccharification of switchgrass led to a 3.1- and 2.3-fold increase in cellulose digestion relative to the untreated and ultrasonic-assisted fungal pretreated switchgrass samples, respectively.