Ultrasound-Assisted Extraction, Characterization, and Antioxidant Activities of the Polysaccharides from Fermented Astragalus membranaceus

This study aimed to optimize the ultrasound-assisted extraction (UAE) of polysaccharides from fermented <i>Astragalus membranaceus</i> (FAPS) and to investigate the physicochemical properties and antioxidant activities of the extracted polysaccharides. Using a combination of single-factor experiments and response surface methodology based on a Box-Behnken design, we improved the extraction of crude FAPS without deproteinization. Under optimal conditions (50 °C, 60 min, 8 mL/g, 480 W), the yield of crude FAPS obtained by UAE (7.35% ± 0.08) exceeded the yield from convectional hot water extraction (6.95% ± 0.24). After protein removal, the FAPS was subjected to comprehensive chemical analyses, including HPLC, HPGPC, FT-IR, UV spectroscopy, and a Congo red assay. The results showed that FAPS had a significantly higher carbohydrate content compared to the non-fermented group (95.38% ± 6.20% vs. 90.938% ± 3.80%), while the protein content was significantly lower than that of the non-fermented <i>Astragalus</i> polysaccharides (APS) group (1.26% ± 0.34% vs. 6.76% ± 0.87%). In addition, FAPS had a higher average molecular weight and a lower Mw/Mn ratio compared to APS. The primary monosaccharides in FAPS were identified as Glc, Ara, Gal and GalA, with a molar ratio of 379.72:13.26:7.75:6.78, and FAPS lacked a triple helix structure. In vitro, antioxidant assays showed that FAPS possessed superior antioxidant properties compared to APS. These results emphasize the significant potential of FAPS as an antioxidant, possibly superior to that of APS. The results of this study suggest that fermentation and UAE offer promising applications for the development and utilization of <i>Astragalus membranaceus</i> for human and animal health.