Rhamnogalacturonan I-Enriched Pectin, Flavonoids, and Alkaloids from Lotus Leaf Infusion in Regulating Glycolipid Absorption and Metabolism: Isolation, In Vitro Bioactivity Verification, and Structural Characterization

Lotus leaf is effective in regulating glycolipid absorption and metabolism, but the roles of small-molecule compounds and polysaccharides are unknown. In this study, the small-molecule compounds including flavonoids, alkaloids, and polysaccharides were gradually isolated from lotus leaf infusion by multi-column chromatography and applied to in vitro activity verification and structural characterization. Although flavonoids and alkaloids were effective in inhibiting pancrelipase and α-glucosidase, polysaccharides more effectively bounded bile acids, inhibited cholesterol micelle solubility, and stimulated the growth of Bifidobacterium than lotus leaf infusion. Polysaccharides, presented as spherical conformation in water, were identified as rhamnogalacturonan I-enriched (93%) low-ester pectin with multiple branches mainly composed of arabinan, arabinogalactan-type II, and galactan formed by →3)-Galp-(1→, →5)-Araf-(1→ and →4)-Galp-(1→ residues. Polysaccharides, which were a key constituent of lotus leaf infusion in regulating glycolipid absorption and metabolism, should be paid more attention and developed as a functional food ingredient.