A Novel Hydrophilic Colloidal Polysaccharide from Rosa roxburghii Tratt: Structural Characterization, Rheological Behavior and Immunomodulatory Activity

Rosa roxburghii Tratt is recognized as an edible and medicinal plant valued for its nutritional and medicinal properties. Polysaccharides are among its key bioactive constituents. A homogeneous polysaccharide, designated RTW-1, was extracted and purified from the fruit of Rosa roxburghii Tratt. Its molecular mass was determined by HPLC to be 2.16 × 103 kDa. Monosaccharide composition and methylation analysis showed that RTW-1 is mainly composed of glucose, arabinose, and galacturonic acid in a molar ratio of 1.00:0.48:0.74. The uronic acid content was measured as 55.21%, and the degree of esterification was 58.30%. The glycosidic linkages identified included (→2,3,4)-Manp-(1→, →4)-Arap-(1→, →4)-GalAp-(1→, T-Rhap, →4)-Glcp-(1→, and (→2,3,4)-Xylp-(1→). Shear-thinning behavior was revealed by rheological analysis. At 30 mg/mL, the thixotropic loop area reached 143.8 Pa/s, which was 20 times higher than that at 12 mg/mL. In RAW264.7 macrophages, cell proliferation was promoted by RTW-1. At 80 μg/mL, phagocytic activity was increased by 88%, and NO production was enhanced by 3.1-fold. Concentration-dependent upregulation of TNF-α, IL-6, IL-1β, and IL-10 mRNA expression was observed by qRT-PCR, with maximum increases of 3.2-, 4.1-, 2.8-, and 2.5-fold, respectively. In conclusion, RTW-1 possesses favorable gel-forming and immunostimulatory properties and shows potential for promoting intestinal immune activity, suggesting its promise as a functional food ingredient.