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Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations. The optimum initial cell and sugar concentrations in the batch fermentation were 1 · 10 8 cells ml -1 and 24°Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y ps ) and productivity (Q p ) were 100 g l -1 , 0.42 g g -1 and 1.67 g l -1 h -1 respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar concentration of 24°Bx was one-time substrate feeding, where P, Y ps and Q p were 120 g l -1 , 0.48 g g -1 and 1.11 g l -1 h -1 respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of ethanol concentration and product yield.

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Optimization of three parameters: agitation rate (A; 100, 200 and 300 rpm), aeration rate (B; 0.5, 1.5 and 2.5 vvm) and aeration timing (C; 2, 4 and 6 h), for ethanol production from sweet sorghum juice under very high gravity (VHG, 290 g L−1 of total sugar) conditions by Saccharomyces cerevisiae NP 01 was attempted using an L9 (34) orthogonal array design. The fermentation was carried out at 30 °C in a 2-L bioreactor and the initial yeast cell concentration was approximately 2 × 107 cells mL−1. The results showed that the optimum condition for ethanol fermentation should be A2B3C2 corresponding to agitation rate, 200 rpm; aeration rate, 2.5 vvm and aeration timing, 4 h. The verification experiments under the optimum condition clearly indicated that the aeration and agitation strategies improved ethanol production. The ethanol concentration (P), productivity (Qp) and ethanol yield (Yp/s) were 132.82 ± 1.06 g L−1, 2.55 ± 0.00 g L−1h−1 and 0.50 ± 0.00, respectively. Under the same condition without aeration (agitation rate at 200 rpm), P and Qp were only 118.02 ± 1.19 g L−1 and 2.19 ± 0.04 g L−1h−1, respectively while Yp/s was not different from that under the optimum condition.

Optimization of four parameters, i.e., zinc (Zn 2+ ), magnesium (Mg 2+ ), manganese (Mn 2+ ) and yeast extract for bioethanol production from sweet sorghum juice by Saccharomyces cerevisiae NP 01 under very high gravity (VHG, 270 g·L , respectively.