mathematical expressions taking into account such recirculation in the models to
avoid a sham growth of cell biomass concentration within the fermenter. In addition,
microorganisms undergo stress when cell concentration increases above 100
g/L in the case of yeasts. Another issue to be considered is the substrate inhibition
that limits the utilization of very concentrated media due to factors like catabolic
repression and osmotic pressure exerting a negative influence on cell growth rate.
Therefore, one of the expressions chosen for yeast growth rate (rX) is as follows: