Ultrasound-Assisted Extraction of Soyasaponins from Hypocotyls, and Analysis by LC-ESI-MS

A rapid high-performance liquid chromatographic method with electrospray mass spectrometric detection has been developed for determination of soyasaponins in hypocotyls. Ultrasound-assisted extraction (UAE) was used to prepare the sample, because it was simpler and more effective than conventional extraction methods for extraction of soyasaponins from soybean hypocotyls using methanol, ethanol, or acetonitrile as solvents. Maximum yields of total or individual soyasaponins extracted by UAE were highly dependent on the extraction solvent and on the operating conditions. The maximum amount of total soyasaponins was extracted by use of 40% ethanol in water. The effects of extraction temperature and time were also investigated, and the stability of soyasaponins during UAE was examined. Soyasaponins could be extracted without decomposition from soybean hypocotyls by three-fold UAE with 40% ethanol at 25 °C for 20 min. The calibration plot was linear (r2 > 0.991) in the concentration range 0.01–1.0 mg L−1 for each soyasaponin, with a lower limit of quantification less than 4.0 ng m L−1. Intra-day and inter-day relative standard deviations (RSD) were less than 9.2 and 13.1%, respectively. The method was applied to routine analysis of soyasaponins in hypocotyls.