Xylitol production from xylose by two yeast strains: Sugar tolerance

The kinetics and enzymology ofd-xylose utilization are studied in micro-, semi-, and aerobic batch cultures during growth ofCandida guilliermondii andCandida parapsilosis in the presence of several initial xylose concentrations. The abilities of xylitol accumulation by these two yeast strains are high and similar, although observed under various growth conditions. WithCandida parapsilosis, optimal xylitol production yield (0.74 g/g) was obtained in microaerobiosis with 100 g/L of xylose, whereas optimal conditions to produce xylitol byCandida guilliermondii (0.69 g/g) arose from aerobiosis with 300 g/L of sugar. The different behavior of these yeasts is most probably explained by differences 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 aerobiosis and on the initial xylose concentration and correlate with xylitol accumulation.