Studies On The Ethanol Production From Sweet Sorghum Juice By Saccharomyces Cerevisiae

Sweet sorghum juice is a potential low-cost substrate for ethanol production. In this paper a uniform design method was applied to optimize the concentrations of phosphate, urea, thiamin, EDTA and pH of medium for ethanol production by Saccharomyces cerevisiae, based on analyzing components of sweet sorghum juice. Five predictive mathematical models were established according to different regression methods, including Multinomial Stepwise Regression, Multinomial Stepwise Regression (mutual), Multinomial Stepwise Regressions (square), Partial Least Squares Regression (mutual), Partial and Least Squares Regression (square). The results from respective validated experiments showed that the highest ethanol production was recorded with the optimized conditions based on the Partial and Least Squares Regression, which were phosphate 3 g/1, urea 1 g/1, thiamin 2 mg/1, EDTA 1.2 g/1 and pH 4.4. In the further validated experiments in a 2.51 fermentor, higher ethanol production 13.5%(v/v) and glucose-ethanol conversion 92%were observed; meanwhile it was verified that thiamin played a crucial role in maintaining the stability of pH in the ethanol fermentation process with the optimized conditions by enhancing the catabolism of pyruvate. The seed culture and aeration conditions have been discussed in the paper, which showed that the secondary seed culture of 16 h and changing aeration conditions in stages were suitable for ethanol production from sweet sorghum juice. The initial concentration of the total sugar in the optimum was also investigated and the results exhibited that the higher inhibition on yeast cells growth and ethanol production was obtained under the higher initial concentration of total sugar.The methods for the determination of the concentrations of the NAD+and NADH in yeast cells have been investigated in the paper. We acquired a series of efficient methods including: yeast cells were disrupted by shaking bead, at the same time NAD+and NADH were extracted by acid and alkali respectively, which were then determined by enzymatic cycling.