Increase in Ethanol Production Efficiency from Sweet Sorghum Juice by Saccharomyces cerevisiae

This research aimed to increase ethanol production efficiency from sweet sorghum juice (SSJ) in terms of ethanol productivity (Q(p)) and concentration (P-E) by Saccharomyces cerevisiae. The growth rate of two ethanol-producing yeast strains, i.e., S. cerevisiae NP01 and SSJ01KKU was determined. The specific growth rate and maximum cell counts of SSJ01KKU in SSJ containing 100 g L-1 of total sugars were higher than those of NP01. Urea addition to the SSJ medium did not promote the growth of SSJ01KKU, and its optimum growth temperature was 32 degrees C. Then, central composite design (CCD) in conjunction with response surface methodology (RSM) was used to optimize the initial sugar and urea concentrations in SSJ for the highest Q(p) and P-E values. Ethanol fermentations were carried out in batch mode at 32 degrees C, with an initial cell count of similar to 5x10(7) SSJ01KKU cells mL(-1). The results showed that the optimum conditions for the maximum predicted Qp (2.82 g L-1 h(1)) were 176 g L-1 of sugar and 2.68 g L-1 of urea (condition A); whereas the optimum conditions for the maximum predicted PE value (100.04 g L-1) were sugar and urea concentrations of 227 and 2.94 g L-1, respectively (condition B). When the verification experiments under both conditions were done, the experimentally derived P-E and Q(p) values were very closed to the predicted values. When the initial cell counts for the ethanol fermentations were increased to similar to 1x10(8) cells mL(-1), the P-E values were unchanged, but the Q(p) values increased to 3.65 and 2.93 g L-1 h(-1) for conditions A and B, respectively.