Xylitol production from wood hydrolyzates by entrapped Debaryomyces hansenii and Candida guilliermondii cells

Debaryomyces hansen ii cells were entrapped in Ca-alginate beads and used f or producing xylitol from wood hydrolyzates. Batch experiments showed that bioconversion was severely hindered when Ca-alginate beads were hardened wi th Al3+ solutions. As an alternative to Al3+ hardening, the improvements in both mechanical stability of bioparticles and fermenting ability of the im mobilized system derived from using increased concentrations of sodium algi nate were assessed. The best results were obtained using a 4% (w/v) Na-algi nate solution in the gelification step. This concentration was selected to perform continuous fermentations in a packed-bed reactor using raw or charc oal-treated hydrolyzates (15.5 g of xylose/L) with two different yeasts: Ca ndida guilliermondii and Debaryomyces hansenii. With a final cell concentra tion 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-treat ed hydrolyzates were 0.58 and 0.91 g/L.h, respectively.