Optimization of biotechnological production of xylitol by a Candida tropicalis strain using Response Surface Methodology

Xylitol is known as one of the most commonly used dietary sugars in food and pharmaceutical industries. The common methodology for production of xylitol is a chemical process which requires high energy and is costly. Biotechnological production of xylitol using microorganisms is an alternative process that is environmentally friendly and cost effective. So, the objective of the present study was to optimize biotechnological production of xylitol from xylose using Candida tropicalis NCIM 3119 strain in the framework of Central Composite Design (CCD) and Response Surface Methodology (RSM).
Four independent factors including temperature (27, 32 and 37°C), pH (3, 5 and 7), xylose concentration (30, 50 and 70 g/l) and yeast extract concentration (3, 7.5 and 12 g/l) were selected, and the xylitol yield (Yp/s= gram xylitol per gram xylose utilized) and biomass production were calculated.
Based on the constructed model, maximum expected xylitol yield (Yp/s= 0.73) was achieved when temperature, pH, and xylose and yeast extract concentrations were 32.7°C, 4.7, 54.2 g/l and 12 g/l, respectively. To confirm the calculated model, an experiment for xylitol production by the strain in the optimum condition was designed at Erlenmeyer level. The results showed that observed xylitol yield and concentration and also biomass of the strain were 0.69, 36.7 g/l and 11.1 g/l, respectively, which were in accordance with the model.
Discussion and Based on the results, it could be concluded that the environmental parameters, including nitrogen source, temperature, pH and xylose and nitrogen source concentrations were optimized to enhance biotechnological production of xylitol, and the final concentration of 36.7 g/l xylitol with 0.69 yield efficiency was achieved.