Process Biochemistry 39 (2004) 951–956 Xylitol production by Candida sp.: parameter optimization using Taguchi approach R. Sreenivas Rao a , R.S. Prakasham b , K. Krishna Prasad b , S. Rajesham c , P.N. Sarma b , L. Venkateswar Rao a,∗ a Department of Microbiology, Osmania University, Hyderabad 500 007, India b Biochemical and Environmental Engineering Center, Indian Institute of Chemical Technology, Hyderabad 500 007, India c PRRM Engineering College, Shabad, Ranga Reddy 509 217, India Received 17 December 2002; received in revised form 11 April 2003; accepted 8 June 2003 Abstract Xylitol production parameter optimization using a newly isolated Candida sp. was performed using Test plan L18, available in the form of an orthogonal array and a software for automatic design and analysis of the experiments, both based on Taguchi approach. Optimal levels of physical parameters and key media components namely temperature, pH, agitation, inoculum size, corn steep liquor (CSL), xylose, yeast extract and KH 2 PO 4 were determined. Among the physical parameters, temperature and agitation contribute higher influence. Media components CSL, xylose concentration and KH 2 PO 4 play an important role in the conversion of xylose to xylitol. The yield of xylitol under these optimal conditions was 78.9%. © 2003 Elsevier Ltd. All rights reserved. Keywords: Candida sp.; Optimization; Taguchi method; Xylitol production 1. Introduction Xylitol is a naturally occurring sugar alcohol with a similar sweetening power to sucrose [1]. Due to its unique pharmacological properties, worldwide demand is ever in- creasing [2,3]. It is widely used in chewing gums, candy, soft drinks, ice creams and oral hygiene products to reduce tooth decay and ear infection in children [1–4]. It is used as a sugar substitute for diabetic patients [2]. At present, xylitol is pro- duced by catalytic hydrogenation of xylose or xylose rich hemicellulose hydrolysates [5] using platinum–cobalt/nickel catalyst. This chemical synthesis requires extensive purifi- cation of substrate, high temperature and pressure [5]. In nature, xylitol is the constituent of many fruits and vegeta- bles, such as raspberries, strawberries, yellow plum, lettuce and cauliflower. Due to its low concentration (usually less than 1%), it is not economical to recover xylitol from such products [4]. Biotechnological production of xylitol could be of economic interest and attractive, mainly due to low ∗ Corresponding author. Tel.: +91-40-2768-2246. E-mail address: vrlinga@yahoo.com (L.V. Rao). cost hemicellulosic hydrolysates as potential substrates [6–8]. Several bacteria [9,10], filamentous fungi [11] and yeasts [12–15] are known to produce xylitol. It has been reported that xylitol production is dependent on various process variables like initial inoculum level, type of substrate, me- dia composition, temperature, pH and K L a levels [16–20] and type of microbial species. Kastner et al. [21] reported that the growth of the xylitol producing organism, Can- dida shehatae, is drastically affected when the culture was incubated under anaerobic conditions and a step change from aerobic to anaerobic improved product formation. Working with Candida guilliermondii, Robert et al. [17] showed that highest xylitol production was achieved at 15 l/h K L a, with the regulation of oxygen supply. The case with media and substrate components were similar where addition of monomer sugars alters the induction levels of xylose metabolizing enzymes [22]. These studies indicate that understanding the basic needs or optimization of pa- rameters is an important factor in achieving maximum output. In conventional production optimization procedures, one parameter is altered at a time while keeping the other 0032-9592/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0032-9592(03)00207-3