Structure and Immunoactivity of Low Molecular Weight Pectin-Complex Decorated Diverse Oligosaccharide Domains from Roots of Platycodon grandiflorum (Jacq.) A. DC

As a traditional functional food, Platycodon grandiflorum (Jacq.) A. DC. has long made significant contributions to human health and the prevention of chronic diseases. Herein, a pectin-complex type polysaccharide from P. grandiflorum termed PGP3-2 (M_w = 6.233 × 10³ g/mol) was isolated and purified and further characterized by various chemical, chromatographic, and spectral techniques. The backbone of PGP3-2 was formed by three repeating "→⁴GalA¹→²Rha¹→" units and a homogalacturonan region with degree of polymerization of nine. Characteristically, three distinct oligosaccharide side chains, i.e., arabinooligosaccharide, glucooligosaccharide, and galactooligosaccharide, are embedded in C-4 positions of the 2-rhamnosyl moieties via covalent bonding to form the complex structure domain of PGP3-2. Preliminary bioactivity assays demonstrated that PGP3-2 exhibited an early immunomodulatory activity. This research establishes a robust theoretical basis for the development of P. grandiflorum in both food and medicinal applications.