Xylitol Production from Wood Hydrolyzates 119 Applied Biochemistry and Biotechnology Vol. 81, 1999 Copyright © 1999 by Humana Press Inc. All rights of any nature whatsoever reserved. 0273-2289/99/81/0119/$13.00 119 *Author to whom all correspondence and reprint requests should be addressed. Xylitol Production from Wood Hydrolyzates by Entrapped Debaryomyces hansenii and Candida guilliermondii Cells JOSE MANUEL DOMÍNGUEZ,* ,1 JOSE MANUEL CRUZ, 1 ENRIQUE ROCA, 2 HERMINIA DOMÍNGUEZ, 1 AND JUAN CARLOS PARAJÓ 1 1 Chemical Engineering Department, University of Vigo (Campus Ourense), 32004 Ourense, Spain, E-mail: jmanuel@uvigo.es; 2 Chemical Engineering Department, Instituto de Investigaciones Tecnológicas, University of Santiago de Compostela (Campus Lugo), 27002-Lugo, Spain Received August 28, 1998; Revised December 23, 1998; Accepted December 30, 1998 Abstract Debaryomyces hansenii cells were entrapped in Ca-alginate beads and used for producing xylitol from wood hydrolyzates. Batch experiments showed that bioconversion was severely hindered when Ca-alginate beads were hardened with Al 3+ solutions. As an alternative to Al 3+ hardening, the improvements in both mechanical stability of bioparticles and fermenting ability of the immobilized system derived from using increased concentra- tions of sodium alginate were assessed. The best results were obtained using a 4% (w/v) Na-alginate solution in the gelification step. This concentration was selected to perform continuous fermentations in a packed-bed reactor using raw or charcoal-treated hydrolyzates (15.5 g of xylose/L) with two different yeasts: Candida guilliermondii and Debaryomyces hansenii. With a final cell concentration of about 50 g of cells/L (0.075 g of cells/g of beads), the volumetric productivities reached with these yeasts in media made from charcoal-treated hydrolyzates were 0.58 and 0.91 g/L·h, respectively. Index Entries: Ca-alginate; Candida guilliermondii; Debaryomyces hansenii; hemicellulose hydrolyzate; xylitol. Introduction Xylitol, a five-carbon polyol with high sweetening power, is tolerated by diabetics, has anticariogenic properties, and has been recommended for