Blasting extrusion pretreatment of sweet sorghum bagasse for enhanced enzymatic saccharification and ethanol production using Pichia kudriavzevii ATCC 20,381.

Blasting extrusion pretreatment (BEP) was evaluated for obtaining sugar enriched saccharified extracts from sweet sorghum bagasse (SSB) for ethanol fermentation. A factorial design was used for studying the effect of last barrel zone temperature (T) and screw configuration (SC) on carbohydrate release and extraction yield. The experiment with a higher total carbohydrate release was selected (BEP + ES) for a posterior 72 h fermentation and compared against enzymatic saccharified (ES) SSB without using BEP. Fermentation was performed at 28 °C, pH 5.0 and 10% of solids loading (BEP + ES and ES) using the stress tolerant yeast ATCC 203,081 for ethanol production. In BEP experiments, screw configuration with one polygon element and a shear zone consisting of 7 reverse elements operating at a T of 190 °C resulted in the highest carbohydrate release after enzymatic saccharification, achieving a 3-fold increase compared to control. BEP enhanced carbohydrate availability and lignocellulosic biomass degradation activity (enzymatic saccharification and fermentation). Ethanol production usining with BEP + ES was 8.65-fold higher than the ES control after 72-h fermentation. Higher initial total carbohydrate (3-fold) and fermentable amino nitrogen (FAN) in BEP + ES (12.41-fold higher) improved SSB fermentability and thus ethanol yield. Glucose was fully consumed in the BEP + ES fermentation, while 91.62% was consumed in the ES experiment. Xylose and mannose/arabinose consumption varied by treatment, but displayed the ability to co-utilize pentoses and hexoses during fermentation. Compared to previous traditional twin-screw extrusion and ES, BEP enhanced SSB carbohydrate release during enzymatic saccharification, and carbohydrate consumption and ethanol production during fermentation.