Structural Characterization and Immunomodulatory Activity of Acid-Extracted Polysaccharides from Chestnut ( Castanea Mollissima Blume)

Chestnut (Castanea mollissima Blume) is a nutrient-rich nut; however, the immunomodulatory potential of its polysaccharides remains underexplored. In this study, three extraction methods (hot water, acid, and alkaline) for chestnut polysaccharides were compared in terms of yield and immunomodulatory activity. Two homogeneous polysaccharides, CP-1a and CP-1b, were purified and characterized. Structural analysis revealed that CP-1a possesses a novel backbone of →4)-β-D-Galp-(1→ and →4)-α-D-Glcp-(1→ residues with O-6 branches. In vitro assays with RAW 264.7 cells showed that CP-1a significantly enhanced proliferation, phagocytosis, and M1 polarization by promoting cytokine secretion and activating the TLR4/NF-κB pathway. In vivo, CP-1a restored splenic immune cell proportions and enhanced peritoneal macrophage function in immunosuppressed mice. These findings identify CP-1a as an immunostimulatory chestnut polysaccharide and support its potential for functional foods or therapeutic applications.