Please cite this article in press as: S. Misra, et al., Comparative study on different strategies involved for xylitol purification from culture media fermented by Candida tropicalis, Separ. Purif. Technol. (2011), doi:10.1016/j.seppur.2011.02.018 ARTICLE IN PRESS G Model SEPPUR-10131; No. of Pages 8 Separation and Purification Technology xxx (2011) xxx–xxx Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Comparative study on different strategies involved for xylitol purification from culture media fermented by Candida tropicalis Swati Misra, Pritesh Gupta, Shailendra Raghuwanshi, Kakoli Dutt, R.K. Saxena ∗ Department of Microbiology, University of Delhi South Campus, Benito Juarez Road, New Delhi 110021, India article info Article history: Received 6 November 2010 Received in revised form 16 February 2011 Accepted 19 February 2011 Keywords: Xylitol Fermentation broth Activated charcoal treatment Crystallization Xylitol recovery abstract Xylitol, a sugar substitute, is a high value product for pharmaceutical and food industries and its purifi- cation being of commercial importance. In the present study, the purification of xylitol obtained through Candida tropicalis by fermentation using synthetic xylose and corn cob hemicellulosic hydrolysate as sub- strates were studied for liquid–liquid extraction (21.72 g/l xylitol extracted in 1:5 (v/v) of ethyl acetate) and precipitation (67.44% xylitol recovery along with certain impurities). By this method xylitol recovery is difficult and expensive for large scale processes. Therefore, activated charcoal treatment followed by vaccum concentration and crystallization method for xylitol extraction was evaluated. The optimized conditions obtained for activated charcoal treatment followed by vaccum concentration and crystalliza- tion method were 15.0 g/l of charcoal concentration at 30 ◦ C for 1 h with 10 times super saturation of initial concentration and crystallization temperature of -20 ◦ C for initiation and then at 8 ◦ C yielding 43.97%. After 4 cycles of crystallization, 76.20% and 68.06% xylitol crystallization yield was obtained in 50 ml and 5.0 l of the synthetic xylose fermentation broth by adapted strain of C. tropicalis respectively. The effect of solvents on the crystalline structure of xylitol showed prismatic structure in the presence of ethanol and orthorhombic needles in the presence of tetrahydrofuran. The purity of the xylitol was characterized using 13 C and 1 H nuclear magnetic resonance, mass spectroscopy, and optical rotation, confirming 98.99% purity in a pure crystallized form. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Industries producing polyol sweeteners have registered a grow- ing demand for the consumption of sugar-free and low heat value products. Among these, xylitol is an important sugar substitute with certain interesting physical and chemical properties which make it a high value compound for pharmaceutical, odontological and food industries. At present, large scale commercial production of xylitol is by an expensive catalytic hydrogenation of d-xylose from acid hydrolysis of lignocellulosics [1]. Hence, it is worthwhile to explore an alternative process for the effective production of xyl- itol using micro-organisms which make use of the semi synthetic media [2,3] or detoxified hemicellulosic hydrolysate [4] in order to reduce the manufacturing costs with minimal environmental and energy issues [5]. The recovery and purification of the product exists as a very complicated step in several industrial fermentative processes, which majorly depend on the nature of the product as well as on Abbreviations: NMR, nuclear magnetic resonance; OR, optical rotation; MS, mass spectroscopy; HPLC, high performance liquid chromatography. ∗ Corresponding author. Tel.: +91 11 24116559; fax: +91 11 24115270. E-mail address: rksmicro@hotmail.com (R.K. Saxena). the complex composition of the fermentation broth [6]. In order to recover a product which requires higher purity for commercial- ization [7], it is often implied that important steps characterized by costs even higher than the production process are used. How- ever, in literature on polyols, very little information is available about xylitol recovery [8–10] and mainly reports are related to the obtainment and treatment of the hemicellulosic hydrolysate, its fermentation and metabolic bioconversion [11,12]. Until now, on industrial scale, the xylitol obtained is separated and purified by chromatographic methods [13,14]. Jandera and Churacek [15] used cation exchange resin columns for xylitol separations followed by crystallization at low temperatures of the xylitol-rich solutions. Whereas, Gurgel et al. [8] used both anion and cation exchange resins to purify xylitol from sugarcane bagasse hydrolysate fermen- tation broth and observed a xylitol loss of about 46–57%. However, such techniques tend to be expensive for industrial scale processes. In order to overcome this hurdle, an efficient and econom- ically competitive strategy for xylitol purification and recovery from fermented broth was developed. The purification of solutions by liquid–liquid extraction and precipitation is used in numerous industrial processes in order to recover dissolved substances or to remove undesirable impurities. However, the most efficient strat- egy used for xylitol purification and its extraction is the activated charcoal treatment followed by vaccum concentration and crystal- 1383-5866/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2011.02.018