Phenotypic structure and antioxidant activity of exopolysaccharide produced by Streptococcus thermophilus MGB80-7

Abstract:

[Background] Exopolysaccharide (EPS) is a secondary metabolite produced during the growth and metabolism of lactic acid bacteria. In addition to improving the texture and quality of products, its physiological function has also attracted the interest of scholars in recent years. [Objective] This study intends to explore the characterization and molecular structure of EPS of lactic acid bacteria, and to reveal the relationship between it and the probiotic properties of EPS. [Methods] The EPS produced by Streptococcus thermophilus MGB80-7 was studied. To be specific, the yield of EPS was determined with the phenol-sulfuric acid method. Then the EPS was separated and purified by ion exchange column chromatography and gel molecular sieve chromatography, and the phenotypic structure of EPS was analyzed based on gel chromatography, infrared spectroscopy, and high performance liquid chromatography. As for the antioxidant activity, the ability to scavenge superoxide anion, hydroxyl radical, and DPPH radical was detected. [Results] The EPS yield of MGB80-7 in M17 medium was high, which was (268.25±5.36) mg/mL. After separation and purification, two components were obtained. Among them, the neutral polysaccharide (WPS-807, 1.028×10⁵ Da) was composed of glucose, galactose, and mannose, and a small amount of rhamnose and arabinose, and the acidic polysaccharide (SPS-807, 8.601×10⁴ Da) was made up of complex monosaccharides, which was dominated by mannose, galactose, and arabinose. EPS-807 can scavenge some free radicals, especially the hydroxyl radicals. [Conclusion] The molecular weight and structure of EPS produced by MGB80-7 influence its antioxidant activity. This result lays a basis for further analysis of the structure-activity relationship and antioxidant mechanism of EPS from lactic acid bacteria.

Key words:Streptococcus thermophilus;exopolysaccharide;phenotypic structure;antioxidant properties