The loss of fermentative activity of yeast cells, observed in continuous fermentation experiments at increasing biomass concentration is explained by the assumption that the ethanol-tolerance behaviour of the microorganisms changes if a growth-stabilizing factor limitation is present. A mathematical specification of the relationships existing in this context is given and an improved steady-state productivity model of ethanol production is derived.

A reduced specific ethanol-forming performance of yeast at high biomass concentrations as a result of a changed ethanol-tolerance behaviour of the cells under condition of limitation. I: A theoretical treatment

In growth-factor limited fermentations carried out in continuous high-flow rate fermenters the relationship existing between the specific ethanol formation rate and the ethanol concentration was found to change its characteristics from a linear function into a nonlinear one at high biomass concentrations. The deviation from the linear inhibitory behaviour of the cells was the greater the more the biomass concentration increased. A very good correspondence between the experimentally found productivities of ethanol formation and its adequate values obtained by calculation could be attained by using an improved steady-state productivity model, in which the variability of the function ν=f(P) had been considered

A reduced specific ethanol‐forming performance of yeast at high biomass concentrations as a result of a changed ethanol‐tolerance behaviour of the cells under condition of limitation. II. Proving the effect in high‐flow rate fermentations with saccharomyces cerevisiae Sc 5

The shape of the temperature profile curve of ethanol production changes in the presence of ethanol. So the characteristic points of the curve are shifted to lower values at increasing ethanol concentrations. As a reason for it the potentiation of thermal deactivation effects by ethanol already at lower temperatures is assumed. Compared to it, the activation energy of ethanol for mation in the suboptimal temperature range was found to be unaffected by alcohol.

Effects of temperature on microbial production IV. The influence of ethanol on the temperature‐profile curve of ethanol production

The ethanol-inhibitory behaviour of the yeast Saccharomyces cerevisiae Sc 5 was found to be characterized by a continual-linear relation between the specific ethanol formation rate and the ethanol concentration. Therefore the simple equation 






could be applied for it.



It is shown that this model is correct only then, if all of the process parameters are in their optimum.



Out of the optimum temperature range the characteristics of the function ν = f(P) change in such a way that in regard to the ethanol concentration P twc linear relations exist for each suboptimum temperature: 











and a non-linear equation is current for each superoptimum temperature: 






where bT is also a function of the temperature and always less than 1.



Taking as a basis these equations the specific ethanol formation rate of the used strain can be calculated for the whole biokinetic P/T-sphere of ethanol production.

Effects of temperature on microbial ethanol production. III. The influence of the temperature on the relation existing between the specific ethanol formation rate of the yeast Saccharomyces cerevisiae Sc 5 and the ethanol concentration in the culture medium

U. Becker

Papers

Effects of temperature on microbial ethanol production. III. The influence of the temperature on the relation existing between the specific ethanol formation rate of the yeast Saccharomyces cerevisiae Sc 5 and the ethanol concentration in the culture medium