Structural Characterization and In Vitro Biological Activity of an Extracellular Polysaccharide from Lactobacillus paracasei SMR-0128

Lactobacillus paracasei produces bioactive exopolysaccharides, but their structures remain poorly defined. Here, an exopolysaccharide fraction, LPP (12.3 kDa), was isolated from L. paracasei SMR-0128. LPP was mainly composed of rhamnose and mannose, with glucose, glucuronic acid, N-acetylgalactosamine, arabinose, glucosamine, galactose, and xylose. Methylation and diagnostic NMR data indicated abundant terminal and substituted Rha/Man residues, possible branching sites, and acidic and acetyl/N-acetyl-related features; however, the complete repeating unit could not be resolved. LPP was therefore characterized as a Rha- and Man-rich branched acidic heteropolysaccharide containing multiple terminal and substituted residues, while its complete repeating-unit architecture remained unresolved. Functionally, LPP enhanced phagocytosis, nitric oxide production, and cytokine secretion in RAW264.7 macrophages under basal conditions, while modulating NF-κB-related signaling and reducing selected inflammatory mediators in LPS-stimulated cells. These findings support further investigation of LPP as a probiotic-derived immunostimulatory polysaccharide.