Ability of xilitol production by new yeast strains

Xylitol is a natural sweetener used commercially as a substitute for sucrose, mainly by its low-calorie and anticariogenic properties. Moreover, its metabolism is independent of insulin, which can be used by people with diabetes and obesity problems. Currently, xylitol is produced by catalytic hydrogenation of D-xylose, a costly process because it requires highly purified xylose syrup. As an alternative to the conventional process, xylitol can be obtained from the fermentation of xylose-rich solutions, without the need for prior substrate purification. Several microorganisms have been identified as fermenting xylose to xylitol, among them stand out Penicillium, Aspergillus, Rhizopus, Byssochlamys, Candida, Pichia, Schizosaccharomyces and others. In this study, we analyzed the efficiency and productivity of xylitol production by Issatchenkia occidentalis CCTCC M 206097 and Issatchenkia orientalis CCTCC M 206098 yeasts. The experiments were conducted in triplicate, for 48 hours, in 125 mL flasks with 50 mL of semi-synthetic medium composed by xylose in two different concentrations (12.0 and 50.0 g/L), supplemented with (NH4)2SO4 (2.0 g/L), MgSO4.7H2O (0.2 g/L), K2HPO4 (2.0 g/L), KH2PO4 (6.0 g/L), urea (2.0 g/L), yeast extract (6.0 g/L). The xylose and xylitol concentrations were quantified by liquid chromatography and cell growth was monitored by turbidimetry at 600 nm. After 48 h tests showed a higher cell growth for I. occidentalis yeast for both xylose concentrations. The results showed a higher yield of xylitol (0.23 g/g) when given 12.0 g/L of xylose to I. occidentalis yeast, and a lower yield (0.05 g/g) when given 50.0 g/L of xylose for I. orientalis species. Regarding productivity, the best results were obtained when used 50.0 g/L of xylose for I. occidentalis species (0.067 g/L.h). The results show that tests in bioreactors, with optimized conditions, can result in good yields and productivity in xylitol production by those yeasts.