Effects of Initial pH on Synthesis of Xylitol 751 Applied Biochemistry and Biotechnology Vol. 84–86, 2000 Copyright © 2000 by Humana Press Inc. All rights of any nature whatsoever reserved. 0273-2289/00/84–86/0751/$12.25 751 *Author to whom all correspondence and reprint requests should be addressed. Effects of Initial pH on Biological Synthesis of Xylitol Using Xylose-Rich Hydrolysate TIHANY A. MORITA, SILVIO S. SILVA,* AND MARIA G. A. FELIPE Biotechnology Department, Faculty of Chemical Engineering of Lorena, PO Box 116, Lorena, SP, Brazil, 12600-000, E-mail: silvio@debiq.faenquil.br Abstract Sugarcane bagasse, an agricultural residue plentiful in Brazil, was utilized for xylitol production by a biotechnological process. A medium fermentation prepared with this xylose-rich biomass at an oxygen transfer volumetric coefficient of 10/h 1 and different initial pH values was inoculated with cells of Candida guilliermondii FTI 20037. The maximum values of xylitol and cell volumetric productivities (Q p = 0.56 g/[L·h] and Q x = 0.11 g/[g·h]), xylitol yield factor (Y P/S = 0.79 g/g), and xylose uptake rate (qs = 0.197 g/[g·h]) were attained at pH 7.0 without further pH control. The results show that the yeast performance was influenced by the pH, an important bioengineering parameter in this fermentation process. Index Entries: Sugarcane bagasse hydrolysate; xylitol; detoxification method; pH; fermentative parameters. Introduction Bioconversion processes of xylose present in hemicellulosic hydroly- sates have been extensively developed, utilizing lignocellulosic biomass for the production of chemicals, liquid fuels (1), and feedstocks, such as ethanol and xylitol (2,3). Xylitol, a five-carbon natural polyol (4) of high economic value, has aroused much interest in the food and pharmaceutical industries because it is anticariogenic (5), has negative heat of dissolution (6), and, according to preliminary studies, increases the lactoperoxidase activity, an enzyme that serves the function of defending the human body against pathogenic organisms (7). The biological synthesis of xylitol is a promising alternative to the chemical process, because it uses microbial cells as catalysts and does not require initial xylose purification (8). Among the xylose-rich lignocellulosic materials is sugarcane bagasse, a residue whose production in Brazil reaches 295 million t/yr (9). Most of this biomass is utilized in fuels, but new processes to use the bagasse