Application of a model using the phenomenological approach for prediction of growth and xanthan gum production with sugar cane broth in a batch process

Production of xanthan gum was studied and modelled using unstructured kinetic models composed of three differential equations, which considered the microbial biomass, carbon source, and xanthan concentration. The fermentation process, using Xanthomonas campestris pv. campestris NRRL B-1459, was conducted under controlled conditions with diluted sugar cane broth at different initial sucrose concentrations (15.0, 25.0, and 35.0 gL(-1)). Unstructured kinetic models proposed in the literature for this system were reviewed and applied. These models were tested against the experimental results, calculating the parameters by nonlinear regression. The kinetic models used in this study provided estimations of microbial growth, substrate consumption, and product formation, and, therefore, these parameters were quantified in the fermentation experiments. Higher yield of xanthan per amount of sucrose (0.58 g g(-1)) and productivity (0.63 g L-1 h(-1)) were obtained using initial sucrose concentrations of 25.0 and 35.0 g L-1, respectively. The models were used to predict the kinetic parameters for a medium containing an intermediate and a larger initial sucrose concentration (27.0 and 40.0 g L-1). When tested experimentally, the measured fermentation parameters were in close agreement with the values predicted by the model that presented the best adjustment, demonstrating its validity. (C) 2009 Elsevier Ltd. All rights reserved.