A Novel Polysaccharide from Walnut Dregs: Structural Features and Immunomodulatory Effects via Activation of MAPK Signaling Pathway

A novel acidic polysaccharide (WDP) was purified from walnut dregs, and its structural characteristics and immunomodulatory function were investigated. WDP had a weight-average molecular weight (Mw) of 351.94 kDa and consisted mainly of rhamnose, arabinose, galactose, glucose, xylose, mannose, galacturonic acid, and glucuronic acid. Methylation and NMR analyses further demonstrated that the backbone of WDP comprised →4)-α-D-GalpA-(1→, →3,6)-β-D-Galp-(1→, →6)-β-D-Galp-(1→, →4)-β-D-Galp-(1→, and →4)-α-D-Glcp-(1→ residues, with branched chains consisting of terminal α-L-Araf-(1→ residues or α-L-Araf-(1→5)-α-L-Araf-(1→ fragments attached to the O-3 position of →3,6)-β-D-Galp-(1→ residues. In vitro assays indicated that WDP modulated immune responses in RAW264.7 cells by enhancing their phagocytosis; increasing NO release and the secretion of IL-1β, IL-6 and TNF-α; and activating the MAPK signaling pathway, suggesting its potential as an immunomodulatory agent. These results provide a scientific foundation for the development of walnut dregs-derived functional foods with immune-enhancing properties.