Production and physicochemical characterization of xanthan gum by native lactose consuming isolates of Xanthomonas citri subsp. citri

Xanthan is a biopolymer produced by Xanthomonas bacteria which is widely used in many industries such as food and oil. In this work, three Xanthomonas strains (X. citri/NIGEB-88, X. citri/NIGEB-386 and X. citri/NIGEB-K37) were used to evaluate their industrial potential to produce xanthan gum in whey medium. Bacteria growth rate, viscosity, biomass, dry weigh of produced xanthan and β-galactosidase activity were studied during the fermentation process and the presence of β-galactosidase genes was assessed by PCR technique. Strain NIGEB-386 had the best ability to utilize lactose in the whey medium. The highest amount of xanthan production and viscosity were 22.7 g/l and 2066.6 mPa·s, respectively. The presence of six β-galactosidase genes in strains NIGEB-386 and NIGEB-K37 was confirmed. The pyruvate and acetyl contents in xanthan gum were 2.1 and 0.29 %, respectively. Fourier-transform infrared spectroscopy analysis determined the position of the functional groups in the structure of the fermentation product. In whey medium, the performance of both NIGEB-386 and NIGEB-K37 strains were better than the X. campestris. The findings showed that Xanthomonas citri/NIGEB-386 is suitable for industrial production of xanthan using cheese whey as a low-cost medium.