Production of xylitol from xylose in batch fermentations of Candida mogii ATCC 18364 is discussed in the presence of glucose as the cosubstrate. Various initial ratios of glucose and xylose concentrations are assessed for their impact on yield and rate of production of xylitol. Supplementation with glucose at the beginning of the fermentation increased the specific growth rate, biomass yield and volumetric productivity of xylitol compared with fermentation that used xylose as the sole carbon source. A mathematical model is developed for eventual use in predicting the product formation rate and yield. The model parameters were estimated from experimental observations, using a genetic algorithm. Batch fermentations, which were carried out with xylose alone and a mixture of xylose and glucose, were used to validate the model. The model fitted well with the experimental data of cell growth, substrate consumption and xylitol production.

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A model-based optimization involving a genetic algorithm was used to establish the optimal substrate feeding profiles in fed-batch fermentations for maximizing the average production rate of xylitol from xylose. The best-case feeding profiles were verified experimentally in fermentations fed with glucose and xylose. The model-predicted profiles agreed remarkably well with the measured data even though the model was based on parameter values derived from a batch fermentation.

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