Review of Astragalus membranaceus polysaccharides: Extraction process, structural features, bioactivities and applications

Astragalus membranaceus possesses the function of enhancing immunity, protecting the liver, diuretic, anti-aging, anti-stress, anti-hypertensive, and more extensive antibacterial effects. Polysaccharides, one kind of the major active ingredients of A. membranaceus, are considered to be responsible for their versatile use. Now, a systematic summary of research progress and prospects of polysaccharides from A. membranaceus polysaccharides (AMPs) is necessary to facilitate their further study and application. In this review, the optimal extraction methods, structural features, biological activities, and applications of AMPs were emphasized. The structure-activity relationships are also analyzed and elucidated. Solvent, ultrasonic, microwave, enzyme-assisted, ultra-high pressure, and combined methods have been used to extract AMPs. Among them, solvent extraction is the most commonly used method because it is simple and easy to operate, but the efficiency needs to be improved further. The ultra-high pressure method is the most efficient but has a low economic return. AMPs exhibited various bioactivities, including immunomodulation, antitumor, and antidiabete. The structure-activity relationships revealed that different structure configurations, chain conformations, and physical properties would have different bioactivities. However, the new method for purification of certain polysaccharides, detailed structure-activity relationships (SAR), mechanisms of bioactivities, and quality control of AMPs need to be extensively investigated.