ETHANOL PRODUCTION FROM SORGHUM GRAINS [Sorghum bicolor (L.) MOENCH]: EVALUATION OF THE ENZYMATIC HYDROLYSIS AND THE HYDROLYSATE FERMENTABILITY

The production of ethanol from sorghum grains was investigated in the present work. Initially, starch enzymatic hydrolysis was investigated using commercial alpha-amylase and glucoamylase, considering particle size, solid: liquid ratio and enzyme load as variables. The hydrolysate, in the best conditions (73 U of alpha-amylase/g grain and 1150 U glucoamylase/g grain), contained glucose at a concentration of approximately 250 g/L, which was fermented to produce ethanol in a bioreactor in batch mode. Using an industrial strain of Saccharomyces cerevisiae, the maximum ethanol concentration produced was roughly 106 g.L-1 in 24 h of fermentation, resulting in a volumetric productivity of 4.4 g.L-1.h(-1) and a product yield based on the substrate consumed (0.499 g.g(-1)) close to the theoretical.