Highly Branched Rhamnogalacturonan-I Type Pectin from Wolfberry: Purification, Characterization, and Structure-Prebiotic/Immunomodulatory Activity Relationship

Due to the difficulty in obtaining highly branched rhamnogalacturonan-I (RG-I) type pectin, the relationship between the extent of RG-I branching (EB) of pectin and prebiotic/immunomodulatory activity has not been systematically investigated. Moreover, it is only possible to establish a structure–activity relationship using pectin that is highly purified and accurately characterized. In this study, a homogeneous highly branched RG-I type pectin (LBP-P4, a final product) with dual proliferative effects on Bifidobacterium and macrophage was effectively purified for the first time using enzyme hydrolysis combined with ultrafiltration. The RG-I content and EB of LBP-P4 reached 97.32 and 77.12, respectively. Its two branches were composed of arabinan and arabinogalactan-II, containing → 5)-Araf-(1→, →3)-Araf-(1→, →3,6)-Galp-(1→ and →6)-Galp-(1→ residues). The structure–activity relationship analysis indicated that strong prebiotic/immunomodulatory activity of LBP-P4 was depended on its high EB, which was further confirmed by the molecular docking simulation between low/high branched pectin with β-1,6-galactosidase, α-l-arabinanase, and Toll-like receptor 4 (TLR4).