Optimization of Tween 20 and SDS pretreatment condition for enzymatic hydrolysis of extruded corn stover and prairie cordgrass

Abstract

The extrusion processing has shown potential in previous studies to be used as a pretreatment method for 2nd generation bioethanol production from lignocellulosic biomass. Furthermore, surfactants also have been shown to reduce enzyme deactivation and increase the efficiency of hydrolysis. Therefore, a sequential pretreatment technique was developed in which single screw extruder was used for the first pretreatment according to a previously optimized condition at 90 °C, 180 °C, 180 °C for Corn stover (CS) and 70 °C, 90 °C, 90 °C for Prairie cordgrass (PCG). The temperatures correspond to feed zone, barrel zone and die zone, respectively. The second pretreatment was optimized in this study at 45-55°C, 1-4 h, 0.15-0.6 g Tween 20/g glucan according to response surface methodology. Optimization of surfactant pretreatment facilitated the estimation of interaction and higher order effects for major factors involved in surfactant treatment (temperature, time, surfactant loading). Using moderate dosage of enzyme, the optimum conditions found by fitting appropriate quadratic models to the data increased glucose and xylose yield by 27.5% and 33% for CS and by 21.5 % and 27% for PCG, respectively. Pretreatment of CS and PCG under optimized condition and using 12% g Ctec2/g glucan resulted in 76.2% and 74.4% of glucose yield in CS and PCG, respectively. Surfactant concentrations and pretreatment temperature were the most significant factors affecting the sugar yield for CS and PCG (p value< 0.05). For both CS and PCG, treatment time did not seem to be an important factor for increasing the glucose yield, while it was determined to play a role in maximizing the xylose yield (p value of < 0.1). Studies of SDS concentration on extruded CS and PCG at and beyond CMC level (5.2-100 mM) demonstrated a decrease in sugar yield compare to control; perhaps this occurred due to degradation of enzyme substructures specially a-helixes.