Ultrasonically enhanced extraction of luteolin and apigenin from the leaves of Perilla frutescens (L.) Britt. using liquid carbon dioxide and ethanol

• Luteolin and apigenin were successfully extracted from the leaves of P. frutescens.
• Ultrasound enhances the liquid CO2 and ethanol extraction of luteolin and apigenin.
• In-depth examinations were done into the effect of the operating parameters.
• The ultrasonic cavitation may facilitate the mass transfer of luteolin and apigenin.

The present study reports on the ultrasonic enhancement of the liquid carbon dioxide (CO2) extraction of luteolin and apigenin from the leaves of Perilla frutescens (L.) Britt., to which ethanol is added as a cosolvent. The purpose of this research is also to investigate the effects of the particle size, temperature, pressure, irradiation power, irradiation time, and ethanol content in the liquid CO2 solution on the extraction yield using single-factor experiments. We qualitatively and quantitatively analyzed the yields in the extract using HPLC (high-performance liquid chromatography). The liquid CO2 mixed with ethanol was used at temperatures of 5, 20 and 25 °C with extraction pressures from 8 to 14 MPa. The yields of luteolin and apigenin in the extraction were clearly enhanced by the ultrasound irradiation, but the selectivity of the extract was not changed. The yields of luteolin and apigenin in the extract were also significantly improved by adjusting the operating temperature, the irradiation time, and the ethanol content in the liquid CO2 solution, but no change in the selectivity of the extract was observed.