Modeling of the aerobic growth of Saccharomyces cerevisiae on mixtures of glucose and ethanol in continuous culture.

A structured model dedicated to fed-batch growth of baker's yeast is detailed in steady-state conditions. The simulated results for aerobic growth on mixtures of glucose and ethanol are provided. The model differentiates and identifies glucose utilisation (either oxido-reductive or by oxidation), state 1 and ethanol oxidation, state 2. Ethanol can be oxidised when glucose concentration is below a certain value, s(crit), only; ethanol is excreted when glucose concentration exceeds s(crit). The amount of ethanol co-consumed with glucose is controlled by s(crit) through the transition rate from X1 to X2. Two major novelties are introduced for modeling glucose metabolism. (1) The specific growth rate on glucose is constant, equal to D(crit), at low glucose concentrations, but follows Monod kinetics at high glucose concentrations. (2) Non-constant yields (i.e., Yx/s and Ye/s) are determined by means of dimensionless groups when the specific growth rate on glucose exceeds D(crit). The model is developed on experimentally easily accessible parameters found in the literature for Saccharomyces cerevisiae H1022. A remarkable prediction of the experimental data obtained by Rieger et al. (1983) (J. Gen. Microbiol. 129, 653-661) is highlighted. The simulations suggest that the specific growth rate on ethanol may be underestimated in limited respiratory capacity based models.