Effects of Modifiers on the Supercritical Extraction of Licorice (Glycyrrhiza glabra) and the Morphology of Licorice Tissue

Optimal extraction conditions such as pressures, temperatures, and modifiers on glycyrrhizin extraction from licorice were investigated using supercritical $CO_2\;(SC-CO_2)$ at 3 mL/min flow rate. Morphology of licorice tissue, after glycyrrhizin extraction, was examined by SEM, and absolute density ($g/cm^3$) measurement and glycyrrhizin content were determined by HPLC. Pure $SC-CO_2$ had no effect on glycyrrhizin extraction, but recovery of glycyrrhizin ($32.66{\pm}0.77%$) was enhanced when water was used as modifier. The highest recovery was $97.22{\pm}2.17%$ when 70% (v/v) aqueous methanol was added to 15% (v/v) $SC-CO_2$ at 50 MPa and $60^{\circ}C$. Under optimal extraction conditions, 30 MPa pressure and $60^{\circ}C$ heating temperature, glycyrrhizin recovery reached maximum ($102.67{\pm}1.13%$) within 60 min. Licorice tissue was severely damaged by excessive swelling, and absolute density of licorice residues was highest when aqueous methanol was used as a modifier.