Evaluation and statistical optimization of process variables for xylitol production by Candida kefyr

Xylitol is a pentahydroxypentane, which has high functional properties in food and drug industries. Biotechnology method has been investigated to overcome the drawbacks of xylitol chemical manufacturing. The effect of temperature, agitation speed, pH, and xylose concentration variables on xylitol production by Candida kefyr (ATCC 38296) was studied. The qualitative and quantitative of produced xylitol were evaluated by thin layer chromatography and high-performance liquid chromatography, respectively. The process optimization was done using response surface methodology (RSM) combine statistical experimental factorial designs. The 3D plots of xylitol production were proven to have the dependency and interaction between variables. The predicted results were close to the experimental results, which showed that the quadratic equation obtained from RSM was efficient. The dependency of xylitol yield on the interaction between variables was proven. Optimal levels of process variable were temperature of 28.15ºC, agitation speed of 132.34 rpm, pH value of 6.05, and xylose concentration of 58.90 g/L. On the third day of fermentation, the maximum yield was achieved (15.88 g/L). This is the first report of producing xylitol by Candida kefyr which has strong potential for bioconversion of xylose to xylitol with maximum yield and properties. This natural polyalcohol has desirable physicochemical and functional properties either in foods or in medicines.