Arabinogalacturonan in functional food “Astragalus membranaceus root”: Structure and immunomodulatory activity

Huangqi (Astragalus membranaceus root) is a widely recognized functional food with impressive health benefits. The primary biomacromolecules in A. membranaceus , polysaccharides, are hypothesized to contribute to these health advantages. However, the precise structure and bioactivity of these polysaccharides remain unclear. In this study, the predominant water-soluble polysaccharides were extracted from A. membranaceus root. A homogeneous fraction with molecular weight of 42.0 kDa, designated APS-I, was purified. The monosaccharides of APS-I comprised arabinose and galacturonic acid in a molar ratio of 34:21. The precise structure of APS-I was elucidated by using nuclear magnetic resonance spectroscopy (NMR) and tandem mass spectrometry (MS). The backbone was identified to be α-(1 → 4)-D-galacturonan, which was substituted at O-3 by α-L-Araf-(1→ [5)-α-L-Araf-(1] n → and α-L-Araf-(1→, respectively. This confirmed it as an arabinogalacturonan. The immunomodulatory activity of APS-I was assessed by using macrophage cells. Our findings indicated that arabinogalacturonan could induce NO, IL-6, TNF-α and IL-1β production, demonstrating their potential as an immunoregulatory compound. Notably, TLR4 receptor was involved in the regulation of immune response and may be a target for APS-I.