This study was aimed to compare the ability of some yeast strains to consume sugars (sucrose, glucoseand fructose) and to convert them into ethanol during fermentation. The results of this comparison will be thebasis of considerations in choosing the right strain to be used as a mixed culture to increase the productionof ethanol from substrate containing a mixture of sucrose, glucose and fructose, such as juice of cane andsweet sorghum. The study was conducted using fermentation in substrate consisting of glucose, fructose,and sucrose separately, glucose-fructose mixture, and glucose-fructose-sucrose mixture using some yeaststrains: FNCC3012, OUT7009, OUT7027, OUT7055, OUT7080, OUT7096, OUT7903, OUT7913, and OUT7921.Following the fermentation, analysis of the produced ethanol and the remaining sugar was conducted. Theresults of study indicated that the strains with the highest substrate consumption were OUT7921, OUT7096,OUT7055, OUT7027, and OUT7913 for glucose, fructose, glucose-fructose mixture, sucrose, and glucosefructose-sucrose mixture, respectively. Strains that produced highest concentration ethanol were OUT7096 inglucose and sucrose substrates, OUT7921 in substrate of glucose-fructose mixture and sucrose, OUT7913 insubstrate of glucose-fructose-sucrose mixture. Upon consideration of each strain capacity, both in consumingsugar and producing ethanol, the recommended strains for use in mixed culture in bioethanol fermentationusing mixed substrate of glucose, fructose and sucrose are OUT7096, OUT7913, and OUT7921.

The objective of this study was to evaluate the use of mixed cultures of the recommended yeast strains from a previous study on ethanol fermentation using a substrate mixture consisting of sucrose, glucose, and fructose. There were three mixed (combination) cultures namely OUT7096/OUT7913, OUT7096/OUT7921, and OUT7913/OUT7921. The fermentation medium contained sugar mixture consisting of glucose, fructose, and sucrose with a composition generally close to the composition of sugars in sweet sorghum juice. Overall, fermentation is carried out in two stages. First fermentation was performed using the three mixed cultures to determine the best combination based on the concentration of ethanol produced and the concentration of residual sugar. Second fermentation was conducted using the best mixed culture obtained from the fi rst stage. This second stage was intended to describe the pattern of the changes in the concentration of ethanol, sugars and biomass during the fermentation progresses and to determine some kinetic parameters namely ethanol yield (Y p/s ), growth yield (Y x/s ) and specifi c growth rate (μ). The results of the fi rst fermentation showed that the best mixed culture was OUT7913/OUT7921 and the subsequent fermentation using this culture provide the highest ethanol yield (Y p/s ) = 0.47 g.g -1 that was reached at 53 rd hour, growth yield (Y x/s ) = 0.425 g.g -1, and μ = 0.12 hour -1 .