A Pectin Polysaccharide from Arnebia szechenyi Kanitz and Its Digestion Product: Physicochemical Properties and Immunostimulatory and Antioxidant Activities

The root of <i>Arnebia szechenyi</i> Kanitz, known as "Mongolia Zicao," has been widely used in traditional Chinese and Mongolia medicine. Herein, we aimed to characterize a pectin polysaccharide extracted from <i>A. szechenyi Kanitz</i> root (ASP), elucidate its structure, and evaluate potential immunomodulatory activities through in vitro assays. Sugar composition analysis and high-performance gel permeation chromatography (HPGPC) revealed that ASP is predominantly composed of GalA (45.44%), Gal (22.13%), and Ara (19.86%) with a homogenous molecular weight of 18.4 kD. ASP was identified as a typical pectin-like polysaccharide containing linear HG domains and potentially linked to complex branches with Ara and Glu residues. The monosaccharide analysis of the digestion product, D-ASP, supported this hypothesis. The Congo red test indicated the absence of a triple-helix structure in ASP and its digestion product D-ASP. ASP exhibited an irregular structure due to the branching fork, which disappeared after digestion, as observed by scanning electron microscopy. Additionally, ASP and D-ASP had certain antioxidant activities and significantly stimulated the release of cytokines (IL-1β, IL-6, TNF-a, NO), macrophage proliferation and phagocytic capability in RAW 264.7 cells in a dose-dependent manner. These findings outline the chemical and biological foundation for the development of novel drug candidates in the food and pharmaceutical industries.