Physical and chemical characterizations of corn stalk resulting from hydrogen peroxide presoaking prior to ammonia fiber expansion pretreatment

To effectively improve enzymatic digestibility of carbohydrate in lignocellulosic biomass, hydrogen peroxide presoaking prior to ammonia fiber expansion (H-AFEX) was applied as pretreatment to corn stalk. Enzymatic hydrolysis using cocktail enzymes including cellulase, β-glucosidase and xylanase at 72h after pretreatment under optimal conditions, the glucan and xylan conversions of 88.9% and 86.3% were achieved, respectively. It was about 3.31-fold in sugar yield for H-AFEX-treated corn stalk compared with untreated material. The results of composition analysis and enzymatic hydrolysis showed that H-AFEX pretreatment was effective to remove lignin and improve glucan digestibility. The characteristics of biomass surface and cell wall, biomass crystallinity, and chemical structure changes of H-AFEX-treated corn stalk were determined by digital microscope system, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR), respectively. The results demonstrated that H-AFEX pretreatment induced some morphology changes including partial damages in vascular bundle and deconstruction of cell wall, and the modified biomass structure could increase surface area accessibility and create favorable conditions for enzymatic hydrolysis obviously. Due to removal amorphous substances, the crystallinity index of H-AFEX-treated corn stalk increased comparing with that of raw material. FTIR data showed that H-AFEX process induced changes in chemical structure and cross linking such as removal/dissolution of lignin and hemicelluloses, cleavage of bonds linkage, and decrystallization of cellulose. As a result, H-AFEX pretreatment effectively reduced recalcitrance of corn stalk, and promoted subsequent enzymatic hydrolysis.