A preliminary information about continuous fermentation using cell recycling for improving microbial xylitol production rates - Scientific note

Xylitol is a sugar-alcohol with important technological properties, such as anticariogenicity, low caloric value, and negative dissolution heat. It ca n be used successfully in food formulations and pharmaceutical industries. Its production is therefore in great demand. Biotechnological xylitol produ ction has several economic advantages in comparison with the conventional p rocess based on the chemical reduction of xylose. The efficiency and the pr oductivity of this fermentation chiefly depends on the microorganism and th e process conditions employed. In this article a simple continuous culture with cell recycling was evaluated to enhance the capability of Candida guil liermondii FTI 20037 to produce xylitol. The fermentation was initiated bat chwise by directly inoculating the grown seed culture in a 2-L bench-scale fermenter. Continuous feeding was begun at a dilution rate (D) of 0.060/h a fter the xylose concentration had completely consumed and the cell concentr ation was about 4.0 g/L. At a dilution rate of 0.060/h the xylitol concentr ation was about 15 g/L and increased by about 35%, whereas the dilution rat e decreased by about 58%. Furthermore, the volumetric productivity, Q(p), m arkedly depended on the dilution rate, diminishing by about 37% as D was ch anged from 0.060 to 0.025/h. These preliminary results show us that the con tinuous fermentation with cell recycling is a good way to study the xylitol production by xylose-fermenting yeasts.