Enzymatic saccharification of high pressure assist-alkali pretreated cotton stalk and structural characterization

• Cotton stalk was pretreated by high pressure assist-alkali pretreatment method.
• Enzymatic saccharification parameters of pretreated cotton stalk were investigated.
• Maximum sugar yield was 54.7 g/100 g of biomass cellulose under optimized conditions.
• Changes in cellulose crystallinity of cotton stalk were observed.

Cotton stalk is a potential biomass for bioethanol production, while the conversion of direct saccharification or biotransformation of cotton stalk is extremely low due to the recalcitrant nature of lignocellulose. To enhance the enzymatic conversion of cotton stalks, the enzymatic saccharification parameters of high pressure assist-alkali pretreatment (HPAP) cotton stalk were optimized in the present study. Results indicated that a maximum reducing sugar yield of 54.7 g/100 g dry biomass cellulose was achieved at a substrate concentration of 2%, 100 rpm agitation, 0.6 g/g enzyme loading, 40 °C hydrolysis temperature, 50 h saccharification time, and pH 5.0. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were used to identify structural changes in native, pretreated biomass and hydrolyzed residues. Structural analysis revealed large part of amorphous cellulose and partial crystalline cellulose in the HPAP cotton stalk were hydrolyzed during enzymatic treatment. HPAP cotton stalk can be used as a potential feed stock for bioethanol production.