XYLITOL PRODUCTION FROM XYLOSE BY 2 YEAST STRAINS - SUGAR TOLERANCE

The kinetics and enzymology Of D-Xylose utilization are studied in mic ro-, semi-, and aerobic batch cultures during growth of Candida guilli ermondii and Candida parapsilosis in the presence of several initial x ylose concentrations. The abilities of xylitol accumulation by these t wo yeast strains are high and similar, although observed under various growth conditions. With Candida parapsilosis, optimal xylitol product ion yield (0.74 g/g) was obtained in microaerobiosis with 100 g/L of x ylose, whereas optimal conditions to produce xylitol by Candida guilli ermondii (0.69 g/g) arose from aerobiosis with 300 g/L of sugar. The d ifferent behavior of these yeasts is most probably explained by differ ences in the nature of the initial step of xylose metabolism: a NADPH- linked xylose reductase activity is measured with a weaker NADH-linked activity. These activities seem to be dependent on the degree of aero biosis and on the initial xylose concentration and correlate with xyli tol accumulation.