Characterisation and bioactivity analysis of exopolysaccharides from Lactiplantibacillus plantarum L3

This study systematically investigated the structural characteristics and functional properties of exopolysaccharides (EPS) produced by Lactiplantibacillus plantarum L 3 , focusing on their immunomodulatory and antioxidant potential. The EPS, with a molecular weight (Mw) of 79.93 kDa, was composed of diverse monosaccharides, including d -glucose, d -glucosamine, d -mannose, d -galactose, l -rhamnose, d -xylose, d -glucuronic acid, d -galacturonic acid, l -fucose, l -guluronic acid, d -mannuronic acid, and d -ribose, in molar ratios of 397.403: 236.233: 148.526: 52.448: 46.485: 25.344: 6.902: 4.290: 2.158: 1.533: 1.117:0.619: 0.545. Structural analyses using FT-IR, Raman and NMR revealed the presence of both α- and β-glycosidic bonds, while X-ray diffraction indicated an amorphous structure. The Congo red assay confirmed a triple-helix conformation, and scanning electrical microscopy (SEM) and atomic force microscopy (AFM) imaging demonstrated a highly branched and rough surface morphology. Thermal analysis revealed EPS decomposition at 216.33 °C and 260.45 °C, indicating good thermal stability. In vitro experiments using RAW264.7 cells demonstrated that EPS (200–400 µg/mL) significantly enhanced nitric oxide (NO) production and pro-inflammatory cytokine secretion (TNF-α and IL-6), while also increasing the activities of antioxidant enzymes (SOD, CAT, and GSH-Px), highlighting its potent antioxidant capacity. At a higher concentration (600 µg/mL), EPS exhibited anti-inflammatory effects by promoting IL-10 secretion, suggesting a balanced immunomodulatory function. These findings underscore the potential of L. plantarum L 3 EPS as a promising postbiotic agent with dual antioxidant and immunomodulatory properties.