Growth model and prediction of oxygen transfer rate for xylitol production from d-xylose by C. guilliermondii

Abstract

The K L a values for optimum xylitol productivity using Candida guilliermondii with initial cell concentrations of 1.0 and 4.0 g/l and an initial d-xylose concentration of 50 g/l were predicted as 20 and 100 h −1, respectively, by means of growth, substrate and oxygen uptake simulations. The highest xylitol production rate (1.52 g/l h) was experimentally obtained with an initial cell concentration of 4 g/l and K L a 100 h −1. Kinetic parameters were estimated for Monod, Contois and Tessier growth models using a non-linear method. The Contois model was chosen as the most suitable due to the agreement with data reported in literature for yeasts and statistical confidence of its parameters. The specific oxygen uptake rate (SOUR) was determined by the dynamic oxygen balance. It had a maximum value of 153 mg O 2/g cell h after 2 h growth. The choice of the best K L a value was made through dissolved oxygen concentration simulations for fermentations carried out with two different inoculum sizes, resulting in a maximum volumetric productivity of 1.52 g/l h, for an initial cell concentration of 4 g/l, employing a K L a value of 100 h −1.