Poster Presentation 2-15

Production of Xylitol in Repeated Fed-Batch Fermentation

by Flocculating Yeast, Candida sp. HY200

Heui-Yun Kang¹, Jin-Ho Seo² and Yeon-Woo Ryu¹*

¹Department of Molecular Science and Technology

Ajou University

Suwon, 443-749, Korea

Phone: +82-31-219-2449

Fax: +82-31-216-8777

E-mail: ywryu@ajou.ac.kr

²Department of Food Science and Technology

Seoul National University

Seoul, 151-742, Korea

Repeated fed-batch fermentation for xylitol production was carried out in a two-stage process with flocculating yeast, Candida tropicalis HY200. A series of cell-recycle experiments showed that removal of the medium depleted of substrate precipitating cells and supplying a fresh medium with xylose, yeast extract and minerals for the xylitol production was most effective in enhancing xylitol productivity. The conditions of flocculation were that (1) C/N ratio was over 10 in the initial fermentation medium, (2) pH value was under 4, (3) Ca²⁺ concentration was 10mM and (4) ethanol concentration was under 5 g/l in the medium. The optimized repeat fed-batch fermentation resulted in 0.68 g-xylitol /g-xylose yield and 3.92 g-xylitol l^-1h^-1 productivity. These results were 1.52 times higher in volumetric xylitol productivity and 1.25 times shorter in substrate consumption time compared with the corresponding values of the optimized batch culture.