Jing Cheng, Qianhui Liu, Rui Zhu, Dedian Yu, Lixia Chen, Hua Li
Astragalus membranaceus polysaccharides (APS), bioactive macromolecules derived from the roots of Astragalus membranaceus (Fisch.) Bge., exert immunomodulatory, anti-inflammatory, antioxidant, and metabolic regulatory effects. However, the molecular features and compositional profiles of APS are strongly influenced by extraction procedures, purification strategies, and subsequent chemical or physical modifications. This review comprehensively evaluates APS extraction, structural characterization, biological activities, and application, with particular emphasis on the evidence linking preparation-dependent structural variation to biological responses. Emerging extraction strategies may enhance recycling efficiency; however, there is insufficient reporting on their relevance to polysaccharide integrity, residual solvent safety, and large-scale reproducibility. Structurally, APS comprises diverse polysaccharide architectures, including α-(1 → 4)-D-glucan-like regions, pectic domains such as rhamnogalacturonan I and homogalacturonan, and arabinogalactan-related side chains. Available evidence suggests that molecular weight, monosaccharide composition, branching architecture, and chemical modification may influence biological responses. However, because many APS preparations remain incompletely characterized and structural and bioactivity analyses are often conducted across different studies or non-comparable fractions, causal structure-activity relationships remain difficult to establish. Reported biological activities are mainly supported by cellular and animal studies and involve immune regulation, redox modulation, metabolic regulation, and gut microbiota-associated mechanisms. Future studies should integrate reproducible APS preparation with standardized structural characterization, mechanistic validation, and clinical evaluation to better define the links between preparation, structural variation, and biological activity.