Improvement of xylitol production by controlling oxygen supply in Candida parapsilosis

Abstract

Fermentor experiments were carried in which the oxygen transfer coefficient ( k L a) was varied in order to examine quantitatively the effect of oxygen on xylitol production. When the k L a was increased from 20 to 85 h −1, the cell concentration increased. However, the maximum production of xylitol from 50 g/ l xylose, 35.8 g/ l, was achieved at 62 h at k L a of 30 h −1. Cultures for xylitol production were also carried out under controlled DO concentrations. The cell concentration and xylitol dehydrogenase activity increased with increasing the DO concentration. At a high level of xylitol dehydrogenase activity, most of the xylitol was converted into xylulose, which was metabolized to cell material. The maximum xylitol production from 50 g/ l xylose, 36 g/ l, was obtained after 54 h and the activity of xylose reductase was maximum at a DO concentration of 0.7%, indicating that the DO concentration must be carefully controlled for efficient xylitol production from xylose. By controlling the DO concentration in the range from 0.8 to 1.2%, a final xylitol concentration of 210 g/ l which corresponded to a xylitol yield of 70%, was obtained from 300 g/ l xylose in 66 h.