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 °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 .