ABSTRACT
This work presents a mathematical model that describes of the behavior of the main variable involved in the continuous bioconversion of xylose to xylitol by Candida guilliermondii in a stirred-tank bioreactor with total cell recycle, a promising process to obtain this polyol because it increases productivity in function of the high cellular density. The fermentation system was modeled considering cellular mass, xylose, xylitol and dissolved oxygen concentrations, as well as xylose reductase enzymatic activit as dependent variables. The model is based on the assumption of the intra/extracellular xylitol transport and it is able to represent inhibition by xylose on the main intracellular reaction (conversion of xylose to xylitol by xylose reductase) as well as the influence of the oxygen limitation in all steps of the bioconversion. The results of the mathamatical model simulation were compared to experimental data. The model represents quite well the yeast performance in the production of xylitol.