Viscosity reduction of cassava for very high gravity ethanol fermentation using cell wall degrading enzymes from Aspergillus aculeatus

Abstract

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 2h reduced viscosity to the operating level of <500mPas, 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 96h 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.