Natural deep eutectic solvent-ultrasonic-enzyme combination assisted extraction: Establishment of an integrated method and application on Astragalus polysaccharides

Astragalus polysaccharide (APS) is among the main active components in Astragalus membranaceus (AM), which is an important industrial crop widely used both as medicine and food in East Asia. To improve the extraction yield and quality of APS, a novel, concise and efficient extraction method, namely NaDES-Ultrasound-Enzyme combination assisted extraction (NUECAE), was established for APS in present study. The extraction parameters were optimized, and purified homogeneous polysaccharides were obtained with column chromatography. The structure features and bioactivities of APS obtained both with traditional methods (tAPS) and novel methods (nAPS) were evaluated in comparison. The results revealed that under the optimal extraction parameters: ChCl-Lac content 10 %, solid-liquid ratio 1:30 (g/mL), cellulase (1 U/mg), extraction time 30 min, and extraction temperature 75 °C, the extraction yield of APS was 14.3 %, which was almost twice as high as that of traditional heated water extraction (HWE, 7.6 %). Three homogeneous polysaccharides were isolated from nAPS and tAPS, respectively. The average molecular weight of nAPS were relatively smaller, while monosaccharide analysis showed that the monosaccharide type of both APS are almost the same, but the relative contents were altered. In addition, nAPS exhibited slightly stronger antioxidant activity in vitro. In comparison with reported methods, NUECAE is an innovative, efficient, and environmentally-friendly method for the extraction of polysaccharides from herbal resources. Specifically, the integrated method requires lower time, temperature, and energy consumption, while it can exhibit sharply higher yield and provide higher quality polysaccharide extracts.