Ultrasound‐assisted extraction of ginsenosides in supercritical CO2 reverse microemulsions

Ultrasound‐assisted extraction of ginsenosides from ginseng in supercritical CO2 reverse microemulsions formed by bis(2‐ethylhexyl) sodium sulfosuccinate (AOT) was studied. Prior to extraction the ginseng was soaked in water for 12 h. It was found that ultrasound significantly enhanced supercritical CO2 reverse microemulsion extraction. The ginsenoside extraction yield from supercritical CO2 reverse microemulsion with ultrasound of 20 kHz, 15.2 W cm−2 and 3/6 s was 2.63 times that without ultrasound at 24 MPa extraction pressure, 45 °C extraction temperature, 4 h extraction time, 5 MPa separation pressure, 55 °C separation temperature and 2 L h−1 CO2 flow rate with 140 mL of 0.07 mol L−1 AOT/ethanol. The maximum extraction yields of ginsenosides from different concentrations of reverse microemulsions were obtained at different ultrasonic intensities. The extraction yield with 20 kHz ultrasound was higher than that with 38 kHz ultrasound at suitably low intensity; however, it was lower at high intensity. The yield improvement may be basically attributed to the mechanical and thermal effects of ultrasound.