Characterization of a postbiotic exopolysaccharide produced by Lacticaseibacillus paracasei ET-22 with antioxidant and anti-inflammatory efficacy

Exopolysaccharides (EPSs) produced by lactic acid bacteria have been extensively studied, but the EPSs as postbiotics are much less investigated. In this study, the EPS, designated as ET22-EPS, was extracted and purified from the culture broth of Lacticaseibacillus paracasei ET-22 previously characterized with strong postbiotic activities. ET22-EPS was determined with a molecular weight of 5.12 × 10 5  Da, and a monosaccharide composition of mannose, galactose, glucose, and N -acetylglucosamine in a molar ratio of 0.662:0.103:0.095:0.026. ET22-EPS exhibited a sheet-like and fibrous stacking morphology with a networked structure. ET22-EPS also showed high thermal stability with a degradation temperature of 295.33 °C. ET22-EPS was identified to consist of an octasaccharide repeating unit with a backbone structure of four consecutively linked →2)-α-D-Man p (1 → together with →2,6)-α-D-Man p (1 → 2)-α-D-Glc p (1→, and a branch chain of α-D-Gal p (1 → 6)-α-D-Man p (1→. The in vitro bioassay indicated that ET22-EPS effectively scavenged the free radicals of diammonium 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate), 1,1-diphenyl-2-picrylhydrazyl, hydroxyls, and superoxide anion. ET22-EPS showed strong anti-inflammatory effects by reducing cell phagocytosis, nitric oxide production, pro-inflammatory cytokine secretion, and the TNF-α/IL-10 ratio in a RAW264.7 cell model. Therefore, ET-22-EPS shows good prospects as potential postbiotics in the development of health foods.