Improvement of Bioethanol Production from Sweet Sorghum Juice under Very High Gravity Fermentation: Effect of Nitrogen, Osmoprotectant, and Aeration
To improve ethanol production fermentation efficiency from sweet sorghum juice under a very high gravity (VHG, 280 g/L of total sugar) condition by Saccharomyces cerevisiae NP01, dried spent yeast (DSY), yeast extract, and glycine concentrations were optimized using an L9 (34) orthogonal array design. The results showed that the order of influence on the ethanol concentration (PE) was yeast extract > glycine > DSY. The optimal nutrient concentrations for ethanol production were determined as
... lows: yeast extract, 3; DSY, 4; and glycine, 5 g/L. When a verification experiment under the projected optimal conditions was done, the P, ethanol yield (Yp/s), and ethanol productivity (Qp) values were 120.1 g/L, 0.47, and 2.50 g/L·h, respectively. These values were similar to those of the positive control experiment with yeast extract supplementation at 9 g/L. The yeast viability under the optimal condition was higher than that of the control experiment. To improve sugar utilization and ethanol production, aeration at 2.5 vvm for 4 h was applied under the optimal nutrient supplementation. The P, Yp/s, and Qp values were significantly increased to 134.3 g/L, 0.50, and 2.80 g/L·h, respectively.