Viscosity reduction of cassava for very high gravity ethanol fermentation using cell wall degrading enzymes from Aspergillus aculeatus
•A mixture of cell wall degrading enzymes was prepared from Aspergillus aculeatus.•Proteomic study of secretome showed a complex mixture of glycosyl hydrolases.•The multi-enzyme efficiently reduced viscosity of root mash, chips, and pulp.•VHG SSF of root mash using conventional thermal process led to 19.65% (v/v) ethanol.•VHG SSF of root mash with alternative un-cooked process led to 17.54% (v/v) ethanol.
Cassava is an important feedstock for bioethanol production; however, its use in very high gravity (VHG) fermentation is limited by the high viscosity of mash due to the presence of plant cell wall derived polysaccharides. In this study, viscosity reduction of cassava root mash, chips, and pulp was achieved using a mixture of cell wall degrading enzymes prepared from solid state fermentation of Aspergillus aculeatus BCC17849. Proteomic analysis showed the mixture contained endo- and exo-acting cellulases, hemicellulases, and pectinases from various glycosyl hydrolase families. Enzymatic pretreatment of cassava substrates with the enzyme mixture containing endoglucanase, FPase, xylanase, polygalacturonase, β-glucanase, and mannanase activities at 45 °C, pH 5.0 for 2 h reduced viscosity to the operating level of <500 mPa s, equivalent to the final viscosity of 3.0–51.3% of the initial levels. Simultaneous saccharification and fermentation of the pretreated root mash (32% initial solid) by Saccharomyces cerevisiae with a conventional high-temperature liquefaction process and an uncooked process using a raw starch degrading amylase at 32 °C for 96 h led to a final ethanol concentration of 19.65 and 17.54% (v/v), respectively. The results demonstrated potential of the enzyme for improving process efficiency and economics in VHG bioethanol production.
Journal: Process Biochemistry - Volume 49, Issue 11, November 2014, Pages 1950–1957