Optimisation of the microwave-assisted extraction process for four main astragalosides in Radix Astragali

An efficient microwave-assisted extraction (MAE) technique was employed in extracting astragalosides I–IV from Radix Astragali. Astragalosides were quantified by liquid chromatography-electrospray ionisation mass spectrometry (LC-ESI/MS). The MAE procedure was optimised, validated and compared with other conventional extraction techniques. MAE gave the best result due to the highest extraction efficiency within the shortest extraction time. The optimal conditions of MAE were: employing 80% ethanol as solvent, ratio of solid/liquid 1:25 (g/ml), temperature 70 °C, irradiation power 700 W and three extraction cycles, each 5 min. Scanning electron microscopy (SEM) images of Radix Astragali materials after different extractions were obtained to provide visual evidence of the disruption effect. This is the first report on combining MAE with LC-ESI/MS for the extraction and quantification of astragalosides I–IV in Radix Astragali. The developed MAE method provided a good alternative for the extraction of triterpenoid saponins in Radix Astragali as well as other herbs.