A new approach to model the influence of stirring intensity on ethanol production by a flocculant yeast grown on cashew apple juice

In this work, a rigorous mathematical model was developed, aiming to address a major flaw inherent in most fermentation models found in the literature, which is the inability to accurately account for mass transfer effects. This model was based on the hypothesis of the existence of a stagnant film involving the cell where the mass transfer rate of the substrate flowing from the medium to the cell surface is equal to the rate of substrate consumption by the cells. The model was used to explore the influence of stirring speed, substrate, and initial cell concentrations and temperature on ethanol production by the flocculant yeast Saccharomyces cerevisiae CCA008, grown on cashew apple juice. Model parameters were estimated and validated against experimental data. The experimental data was divided into two sets: one for parameter optimization using non-linear Marquardt least-squares method; and the other to validate the final form of the model equations. Results have shown that the model herein proposed was capable of accurately describing the production of ethanol by S. cerevisiae flocculant yeast considering the influence of operational conditions, especially the effect of the stirring speed on the fermentation rate.