Chemical and physical characteristics and antioxidant activities of the exopolysaccharide produced by Tibetan kefir grains during milk fermentation

An exopolysaccharide (EPS) accumulated during milk fermentation by Tibetan kefir was isolated and characterised in aspects of structural properties and antioxidant activity in vitro. The EPS presented carboxyl, hydroxyl and carbonyl functional groups in Fourier transform infrared spectroscopy analysis and the composition of glucose and galactose was in a ratio of 1:1.88 by gas chromatography analysis. The EPS had a melting point of 131.46 °C and an endothermic enthalpy change of 209.6 J g⁻¹, indicating good stability on heating. Scanning electron microscopy images of the EPS showed smooth and compact surfaces without pores. The EPS demonstrated high activities in antioxidant activity assays in vitro and in protecting protein from oxidative damage in a concentration-dependent manner. Those unique characteristics imply potential applications in the food industry. In addition, the high antioxidant activities of the EPS indicate it could become a promising natural antioxidant supplement in human diet.