APPARENT LOSS OF SUGAR-TRANSPORT ACTIVITY IN SACCHAROMYCES-CEREVISIAE MAY MAINLY ACCOUNT FOR MAXIMUM ETHANOL-PRODUCTION DURING ALCOHOLIC FERMENTATION

Maximum ethanol productions of two enological yeast strains (Saccharomyces cerevisiae K1 and 738-2) were compared during alcoholic fermentation under conditions where substrate was not a limiting factor. Although strain 738-2 seemed to exhibit the lowest sensitivity to ethanol, the strain K1 showed a higher production of ethanol, and a higher CO2 production rate in presence of ethanol than the strain 738-2. The main differences between these two strains were their kinetics of apparent loss of the hexose transport activity : this phenomenon is sufficient to explain the observed differences in maximum ethanol production. Moreover, these kinetics seemed to be biphasic for the strain K1. This result may be an indication of the existence of two different low-affinity components of hexose transport system in this strain.