Use of Immobilized Candida Cells on Xylitol Production from Sugarcane Bagasse Walter de Carvalho3, Silvio Silvério da Silva3*, Michele Vitolob, Ismael Maciel de Mancilha 3 a Department of Biotechnology, Faculty of Chemical Engineering of Lorena, Lorena, SP, 12600-000, Brazil. Fax: (+55) 1 25533165. E-mail: silvio@debiq.faenquil.br b Faculty of Pharmaceutical Sciences, University of Säo Paulo, Säo Paulo, SP, 05489-900, Brazil * Author for correspondence and reprint requests Z. Naturforsch. 55c, 213-217 (2000); received September 10/December 6, 1999 Immobilization, Candida guilliermondii , Xylitol, Sugarcane Bagasse In this study we used the yeast Candida guilliermondii FTI 20037 immobilized by entrap ment in Ca-alginate beads (2.5-3 mm diameter) for xylitol production from concentrated sugarcane bagasse hemicellulosic hydrolysate in a repeated batch system. The fermentation runs were carried out in 125- and 250-ml Erlenmeyer flasks placed in an orbital shaker at 30 °C and 200 rpm during 72 h, keeping constant the proportion between work volume and flask total volume. According to the results, cell viability was substantially high (98%) in all fermentative cycles. The values of parameters xylitol yield and volumetric productivity increased significantly with the reutilization of the immobilized biocatalysts. The highest val ues of xylitol final concentration (11.05 g/1), yield factor (0.47 gig) and volumetric producti vity (0.22 g/lh) were obtained in 250-ml Erlenmeyer flasks containing 80 ml of medium plus 20 mi of immobilized biocatalysts. The support used in this study (Ca-alginate) presented stability in the experimental conditions used. The results show that the use of immobilized cells is a promising approach for increasing the xylitol production rates. Introduction Xylitol is a polyalcohol with a sweetening power comparable to that of sucrose (Bär, 1986). This poliol, used in provision industries in the Scandi navian countries (Hahn-Hägerdal et al ., 1994), has stood out in the last years for its anticariogenic properties (Pepper and Olinger, 1988) and for its clinical applications as a sugar substitute in cases of diabetes, obesity, deficiency in glucose 6 P dehy drogenase enzyme and problems in the metabo lism of lipids (Ylikahri, 1979). From the discovery of the ability of certain yeasts to ferment xylose as a source of carbon and energy (Schneider et al., 1981; Slininger et al., 1982), the interest of scientists in xylitol pro duction by biotechnological means has increased worldwide, since this process has several advan tages over the conventional chemical process (Ojamo et al., 1988). In fact, several researchers have pursuing the development of an economical and feasible technique for xylitol bioproduction from lignocellulosic materials. The bioconversion of xylose into xylitol can be made by the use of mold, bacteria, yeasts or puri fied enzymes (Winkelhausen and Kuzmanova, 1998). The yeast Candida guilliermondii FTI 20037, selected in our laboratories (Barbosa et al., 1988), has proven suitable for this bioprocess, mainly when lignocellulosic materials like eucalyp tus chips (Felipe et al., 1996a), rice straw (Roberto et al., 1996) and sugarcane bagasse (Silva et al., 1997) are used as sources of xylose. Lignocellulosic biomass is a potential renewable source of carbohydrates that can be used as sub strates in biotechnological processes. Before bio logical utilization, the biomass needs to be hy drolysed in order to remove the sugars from the polymeric fraction. Acid hydrolysis of the hemicel lulosic fraction produces mainly pentose sugars, xylose being the major component (Parajö et al., 1996). Sugarcane bagasse is an appropriate raw material for xylitol production, since its hemicellu losic fraction contains 80% of xylose (Kuhad and Singh, 1993). Besides, from the ecological point of view, the adoption of technologies employing this material would prevent serious storage problems and environmental pollution caused by the sur- phus of bagasse (Burgi, 1988). On the other hand, hemicellulosic hydrolysates obtained through acid hydrolysis contains several inhibitory substances, 0939-5075/2000/0300-0213 $ 06.00 © 2000 Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com • D