Ultrasound-assisted extraction, optimization, isolation, and antioxidant activity analysis of flavonoids from Astragalus membranaceus stems and leaves.

Astragalus membranaceus is a medicinal and edible species in China, with a variety of biological activities. This study evaluated the reuse potential of A. membranaceus waste as a source of food antioxidants. Antioxidant and antifungal activities of flavonoids, polysaccharides, and saponins from A. membranaceus stems and leaves were evaluated. Results showed that inhibition rate of flavonoids on six tested fungi reaches 100 % at a concentration of 5 mg/mL, and the antioxidant test demonstrated satisfactory antioxidant activity. On this basis, an extremely economical ultrasonic-assisted extraction of flavonoids from A. membranaceus stems and leaves was developed and optimized via response surface methodology (RSM). Optimized conditions included an extraction time of 35 min, ethanol concentration of 75 %, liquid-solid ratio of 40 mL/g, and extraction temperature of 58 °C, in which the extraction yield of flavonoids was 22.0270 ± 2.5739 mg/g. The total flavonoids were separated and purified using activity-guided isolation technology, and frac. ccd with strong antioxidant activity were analyzed via HPLC-MS/MS. Results showed that main components are isoquercitrin and astragalin. This study can provide a potential innovative application for the development of natural food antioxidants from A. membranaceus waste.