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Effect of Saccharomyces cerevisiae and Zymomonas mobilis on the co-fermentation of sweet sorghum bagasse hydrolysates pretreated under varying conditions

Ndaba, Busiswa, Chiyanzu, Idan, Marx, Sanette, Obiero, George
Biomass and bioenergy 2014 v.71 pp. 350-356
Saccharomyces cerevisiae, Zymomonas mobilis, bagasse, coculture, ethanol, fermentation, hydrolysates, inoculum, mixed culture, pH, pentoses, sweet sorghum, synergism
Hydrolysates from sweet sorghum bagasse pretreatment normally contains hexose and pentose sugars, and this complex mixture of sugars presents a challenge for a single microorganism to effectively ferment all sugars to ethanol. In this study, synergistic effects on the co-fermentation of the hydrolysates using Sacchromyces cerevisiae and Zymomonas mobilis ATCC31825 at different ratios were studied. An inoculum of mixed cultures (1:3 and 5:10 g/L, Z. mobilis to S. cerevisiae ratios) was investigated. Each mixed culture was added to the hydrolysates at pH 4.8 and incubated 32 °C for 24 h. The mixture of Z. mobilis to S. cerevisiae at 5:10 g/L showed the highest synergistic effect with ethanol yields of 0.5 g/g. Since the yield for co-culture was significantly higher than the sum of yields from each microorganism, the improvements can be directly related to co-fermentation of hydrolysate by S. cerevisiae and Z. mobilis.