Influence of External Factors on Fructose and Glucose Fermentations by Saccharomyces cerevisiae GJ2008

Abstract:

The external factors affecting the differences between fructose and glucose consumptions and fermentations under high concentrations of ethanol were investigated by the effects of hexose ratio，micro-aeration and temperature to provide basis for the alcoholic fermentation of high gravity sugarcane juice. Sugarcane juice was simulated using YPDF medium and fermented under ethanol concentration of 11.2% (v/v) and with an initial yeast number of 1.40×108 cells/mL. The concentrations of fructose and glucose in the process of fermentation were determined by HPLC. Metabolic curves of fructose and glucose fermentation were analyzed and fitted by the area under the curve (AUC) method. The fructose metabolism was seriously impeded by the glucose metabolism under high concentrations of ethanol if the initial glucose was more than 40% of total sugar. Micro-aeration could effectively reduce the differences between fructose and glucose consumptions during the late stages of the fermentation，and the ethanol productivity was raised by 61.70%. Low temperature was apparently favorable to maintain the final biomass，while sugar metabolism was susceptible to the endogenous ethanol rather than the exogenous ethanol. In addition，there was a preference to glucose for S.cerevisiae GJ2008，however，the preference was not affected by the environmental factors. For the alcoholic fermentation of high gravity sugarcane juice，it is recommended to maintain a micro-aeration and a low temperature condition during the late stages of the fermentation，in which stages the glucose concentration should be well reduced to remove its metabolic repression to fructose.