Fermentative production of xylitol in a pilot fermentor

In recent days xylitol has been one of the most important sugaralcohol. It is in the focus of biotechnological and microbiological research, because xylitol has a wide variety in use. Xylitol is used for flavoring chewing gums and sweets, as it has positive effect on teeth. It is not consumable by bacteria in the mouth, and it has a caries reducing impact. It could also play a key role in the prevention and medical attendance of diabetes. Xylitol can be derived from biomass. After the acidic hydrolysis of hemicellulose the obtained xylose is converted into xylitol in catalytic or fermentative ways. The second method can be carried out by yeasts and ray fungi.

In this study fermentations carried out in a 30-L pilot fermentor are presented. Candida strains are used as fermenting microorganism. The experiments are carried out on synthetic xylose solution and hydrolysate of corn fibre. The fermentation can be divided into: a) the growth of yeast cells, and b) the conversion of xylose into xylitol. During the first phase aerobic conditions (2 VVM, 400 rpm) are applied to obtain 4-6 g/l cell concentration after 6-7 hours. The length of the second phase depends on the obtained cell mass concentration, and the remaining concentration of xylose. At this stage aeration and stirring are reduced to 0.8 VVM and 150 rpm, respectively, to ensure semi-aerobic conditions. During both phases pH 5.5 and 30°C are maintained. Xylose consumption and formation of xylitol and by-products are monitored in the process.