Effects of Temperature on Fructose and Glucose Utilization during Ethanol Fermentation by S. cerevisiae GJ2008

To solve the problems associated with sluggish and stuck sugarcane fermentation due to high levels of residual fructose, it is necessary to find the reasons why yeast stop using fructose during late fermentation stage. In the experiments, YPDF culture medium was used to simulate ethanol fermentation by sugarcane juice at six different temperatures ranging from 20 ℃ to 36 ℃, and the change of each parameter along the fermentation process was determined, then curve fitting of fructose consumption and glucose consumption was done, and complete metabolism/half metabolism time of glucose/fructose was calculated through the fitting equation. We found that temperature had an important impact on fructose and glucose consumption, S.cerevisiae GJ2008 always showed a slightly higher preference for glucose than fructose at temperature ranging from 20 ℃ to 36 ℃, but once glucose was low enough, fructose consumption sped up drastically due to the competitive inhibition released by glucose. The main reason why fructose utilization stuck we could explain is the competitive inhibition produced by the presence of glucose during the late stage of fructose and glucose co-fermentation. Meanwhile, fructose was less strongly affected by temperature decrease and lower temperature could relieve sluggish phenomenon. The optimum temperature for maximum ethanol production in YPDF medium was at 28 ℃(fermenting time was 28 h) with ethanol yield of 3.89 g/L·h. Those data are important for industrial assessment of sugarcane fermentation.