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

The root of Arnebia szechenyi 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 A. szechenyi Kanitz 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.