Abstract
The influence of temperature (15ยฐ โ40ยฐC) and pH (2.5โ6.0) on the continuous growth of bakers' yeast (Saccharomyces cerevisiae) at steady state in 1% ethanol was investigated. Optimal temperature and pH were 30ยฐC and 4.5, respectively. The shortโterm effect of ethanol concentration (0.1โ10.0%) on the yeast growth was assessed in batch culture. Up to 1% of ethanol, the yeast growth increased in function of the ethanol concentration in the medium. The biomass reached a maximum within the interval of 1โ4% of ethanol (7.9 and 31.6 g/L, respectively) and decreased at higher concentrations. The residual ethanol concentration in the medium increased rapidly when the initial ethanol concentration exceeded 4%. The bestโfit model obtained for growth inhibition as a function of ethanol concentrations was that of Tseng and Wayman: ฮผ~m~S/)K + S( โ i (S โ S~ฮธ~). With this model, the specific growth rate (ฮผ) decreased linearly as the ethanol concentration increased between the threshold value (S~ฮธ~) of 11.26 g/L to be fully inhibited at 70.00 g/L (S;) an inhibition constant (i) of 0.0048 g L^โ1^ h^โ1^, a maximum specific growth rate (ฮผ~m~) of 0.284 h^โ1^, and a saturation constant (K) of 0.611 g/L were obtained.