Study of xylitol production by Candida guilliermondii on a bench bioreactor Carla J.S.M. Silva, Solange I. Mussatto, Ine ˆs C. Roberto * Department of Biotechnology, Faculty of Chemical Engineering of Lorena, Rodovia Itajuba ´ -Lorena Km 74,5, Cx Postal 116, 12600-970 Lorena, SP, Brazil Received 1 September 2004; received in revised form 22 March 2005; accepted 14 April 2005 Available online 31 May 2005 Abstract The kinetic behaviour of the yeast Candida guilliermondii FTI 20037 was evaluated on a bench bioreactor using rice straw hydro- lysate as a substrate. The maximum xylitol concentration (45.4 g l 1 ) was attained after 45 h of fermentation, which corresponded to a xylitol volumetric productivity of 1.01 g l 1 h 1 . This value was improved in about 90% when compared to the results attained with aerated flasks (0.54 g l 1 h 1 ). The kinetic results obtained in the present work reinforce the idea that rice straw hydrolysate constitutes an effective xylose source for xylitol production. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Kinetic behaviour; Candida guilliermondii; Rice straw hydrolysate; Xylitol; Xylose; Bioconversion; Bench bioreactor 1. Introduction The development of fermentative processes using carbohydrates from lignocellulosic materials has gener- ated a great deal of interest on a worldwide level for sev- eral decades. In the last few years much attention has been given to the hemicellulosic component of these materials, rich in xylose, with the aim of attaining differ- ent products with high social and economical value. Among these products, xylitol stands out, mainly due to its potential in preventing dental caries (Gaffar et al., 1998) and otitis (Uhari, Kontiokari, & Niemela, 1998) in children. This organic compound, with the gen- eral formula C 5 H 12 O 5 , has a sweetening power similar to that of sucrose, being recommended to obese and dia- betic patients, due to its insulin-independent metabolism (Pepper & Olinger, 1988). It is also used as a food addi- tive to improve colour and texture of products in which it is incorporated, without causing any undesirable change during stocking (Voirol, 1978). This polyol has been produced since the 1970s by catalytic hydrogena- tion of xylose, which results in a high price product (about 10 times of sucrose or sorbitol) due to the exten- sive steps of purification to attain a pure xylose solution, essential to the process. This fact has encouraged the development of new technologies capable of lowering the production costs of this substance. In this field, the microbiological process of xylitol production has been suggested as an alternative, because it does not require extensive steps of xylose purification. The present work evaluated, on a bench fermentor, the kinetic behaviour of the yeast Candida guilliermondii FTI 20037 in rice straw hemicellulosic hydrolysate. The study was performed using an initial xylose concentra- tion (82.5 g l 1 ) and inoculum (3.1 g l 1 ) pre-defined as being the best for cultivation on aerated flasks (Silva & Roberto, 2001). 0260-8774/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.04.001 * Corresponding author. Tel./fax: +55 1231533165. E-mail address: ines@debiq.faenquil.br (I.C. Roberto). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 75 (2006) 115–119