Increasing Bioethanol Yield from Fermentation of Sweet Sorghum (Sorghum bicolor L. Moench) Sap by Mixed Culture Composed of Two Yeast Strains

Abstract

Objectives: To evaluate the performance of the mixed culture of yeast strains to increase ethanol fermentation yield of sweet sorghum sap. Methods/Statistical Analysis:The yeast strains used were OUT7096, OUT7913, and OUT7921 while sweet sorghum saps utilized were KCS105 and FS501. Fermentation was performed in batch process and concentration of ethanol and sugars were determined by HPLC. Performance of each culture was indicated by ethanol yield and sugar conversion efficiency. The best culture was indicated by the best ethanol yield determined based on the one way ANOVA and Least Significant Difference test. Findings: The results showed that the composition of sugars and minerals in the two sweet sorghum saps are good for ethanol fermentation but supplementation with a bit of nitrogen and phosphorus may necessay for optimum yield. On the fermentation of KCS105 sap, all the three mixed culture especially OUT7913/ OUT7921 (1:1) provided higher performance than when used in single. On the fermentation of FS501 sap, the mixed culture of OUT7096/OU79013 (1:1) showed the highest performance among all of the cultures used, despite the data are not significant. The high value of SCE in both fermentation of KCS105 and FS501 saps suggested the oocurence of sugars other than sucrose, glucose and fructose. It was also found that mixed culture of OUT7913/OUT7921 (1:1) was more glucophilic than the mixed culture of OUT7096/OU79013 (1:1) . On the contrary, OUT7913/OUT7921 (1:1) culture was more fructophilic than the culture of OUT7913/OUT7921 (1:1) . Applications/Improvements: Mixed culture may improve ethanol yield of fermentation of substrate containing types of sugar like sweet sorghum sap.