High Level Ethanol Production by Nitrogen and Osmoprotectant Supplementation under Very High Gravity Fermentation Conditions

Optimization of nutrient supplements i.e., yeast extract (1, 3 and 5 g.L-1), dried spent yeast (DSY: 4, 12 and 20 g.L-1) and osmoprotectant (glycine: 1, 3 and 5 g.L-1) to improve the efficiency of ethanol production from a synthetic medium under very high gravity (VHG) fermentation by Saccharomyces cerevisiae NP 01 was performed using a statistical method, an L-9 (3(4)) orthogonal array design. The synthetic medium contained 280 g.L-1 of sucrose as a sole carbon source. When the fermentation was carried out at 30 degrees C, the ethanol concentration (P), yield (Y-p/s) and productivity (Q(p)) without supplementation were 95.3 g.L-1, 0.49 g.g(-1) and 1.70 g.L-1.h(-1), respectively. According to the orthogonal results, the order of influence on the P and Q(p) values were yeast extract > glycine > DSY, and the optimum nutrient concentrations were yeast extract, 3; DSY, 4 and glycine, 5 g.L-1, respectively. The verification experiment using these parameters found that the P, Y-p/s and Q(p) values were 119.9 g.L-1, 0.49 g g(-1) and 2.14 g.L-1.h(-1), respectively. These values were not different from those of the synthetic medium supplemented with 9 g.L-1 of yeast extract, indicating that DSY could be used to replace some amount of yeast extract. When sweet sorghum juice cv. KKU40 containing 280 g.L-1 of total sugar supplemented with the three nutrients at the optimum concentrations was used as the ethanol production medium, the P value (120.0 g.L-1) was not changed, but the Q(p) value was increased to 2.50 g.L-1.h(-1).