Ethanol production by repeated-batch fermentation at high temperature in a molasses medium containing a high concentration of total sugar by a thermotolerant flocculating yeast with improved salt-tolerance

An attempt was made to improve the salt tolerance of the thermotolerant flocculating yeast Saccharomyces cerevisiae strain KF-7 (KF-7) by maintaining a high concentration of KCl in the medium. Among selected strains, K211 had the highest cell viability and ethanol productivity in a molasses medium containing 25% (w/v) total sugar at 35 degrees C. Strain K211 accumulated higher concentrations of glycogen and trehalose than did KF-7, and also remained alive in the stationary phase during batch fermentation in a jar fermenter. As a result of repeated-batch fermentation tests with K211, stable ethanol production was achieved with an ethanol concentration of 92 g/l and a productivity of 3.5 g/l . h at 33 degrees C in 22% molasses medium. With KF-7, stable ethanol production could not be attained under these conditions. In addition, even at the higher temperature of 35 degrees C, strain K211 gave stable ethanol production with an ethanol concentration of 91 g/l and a productivity of 2.7 g/l . h.