Characterization of the antioxidant activities of the exopolysaccharides produced by Streptococcus thermophilus CGMCC 7.179

Streptococcus thermophilus is a traditional starter for yogurt making. Here, an eps gene cluster encoded for exopolysaccharides (EPS) was identified in the genome of S. thermophilus CGMCC 7.179. After purifying by DEAE-Sepharose Fast-Flow column chromatography, three main components ST-ESP1, ST-EPS2 and ST-EPS3, consisted of mannose, glucuronic acid, galacturonic acid, glucose and N-acetylglucosamine, were obtained. ST-EPS2 showed stronger antioxidant activity than the others in vitro. Moreover, ST-EPS2 could significantly upregulate the transcription levels of NF-E2-related factor-2 (Nrf2) and promote the expression of antioxidant-related proteins involved in Nrf2, suggesting ST-EPS2 protected the intestinal epithelial NCM 460 cells by attenuating the intracellular reactive oxygen species (ROS) level rising against oxidative stress. The potential binding mode of the mannose, galacturonic acid and N-acetylglucosamine with Keap1 simulated through molecular docking confirmed the action of ST-EPS2 with the protein Nrf2. Those results demonstrated that the ST-EPS2 provided opportunities for a natural antioxidant agent exploration in the food industry. •Three main components ST-ESP1, ST-EPS2, and ST-EPS3 were obtained by purification.•The preliminary structural features of three EPS components were determined.•ST-EPS2 protected the NCM 460 cells by attenuating the intracellular ROS content.•The binding of three monosaccharides to Keap1 was simulated by molecular docking.