Optimization of Agitation Conditions for Maximum Ethanol Production by Coculture

Abstract

The coculture of Saccharomyces cerevisiae and Candida tropicalis was used for batch ethanol production in a synthetic medium containing 20 g/l glucose and xylose as carbon source. After incubation at 30 °C for 18 h at glucose and xylose ratio 1:0, 8:1, 6:1, 4:1, 2:1, 1:1 and 0:1, the yield of ethanol (Y_p/ S_s) were 0.35, 0.35, 0.34, 0.32, 0.32, 0.27 and 0.05 g/g, respectively. The yield of cell mass were 0.12, 0.09, 0.08, 0.08, 0.10, 0.09 and 0.10 g/g, respectively. The results indicated that the coculture could produce the maximum level of ethanol at the mixture of glucose and xylose ratio 8:1. Batch fermentation with agitation rate 0-200 rpm was studied using mixed glucose and xylose (8:1) under the same condition. The results showed that the yields of ethanol (Y_p/S_s) were 0.33, 0.38, 0.37, 0.35 and 0.33 while the yields of cell mass were 0.04, 0.04, 0.05, 0.09 at the agitation rate of 0, 50, 100, 150 and 200, respectively. The results suggested that the agitation rate of 50 rpm was suitable for ethanol production by the coculture from the mixed sugars.