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

As a traditional functional food, <i>Platycodon grandiflorum</i> (Jacq.) A. DC. has long made significant contributions to human health and the prevention of chronic diseases. Herein, a pectin-complex type polysaccharide from <i>P</i>. <i>grandiflorum</i> termed <b>PGP3-2</b> (<i>M</i>_w = 6.233 × 10³ g/mol) was isolated and purified and further characterized by various chemical, chromatographic, and spectral techniques. The backbone of <b>PGP3-2</b> 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 <i>C</i>-4 positions of the 2-rhamnosyl moieties via covalent bonding to form the complex structure domain of <b>PGP3-2</b>. Preliminary bioactivity assays demonstrated that <b>PGP3-2</b> exhibited an early immunomodulatory activity. This research establishes a robust theoretical basis for the development of <i>P</i>. <i>grandiflorum</i> in both food and medicinal applications.