Microwave-assisted simultaneous extraction of liquiritigenin and glycyrrhizic acid from Licorice (Glycyrrhizae radix et Rhizoma)

Licorice (Glycyrrhizae radix et Rhizoma), one of the oldest and most frequently employed folk medicine in Asia and Europe, is widely used to treat diseases of the respiratory tract, gastrointestinal and cardiovascular system. A large number of metabolites have been isolated from licorice, including triterpene saponins, glycyrrhizic acid is normally being considered to be the main biologically active component. But liquiritin, liquiritigenin, isoliquiritigenin, isoliquiritin and glycyrrhetinic acid have proved to possess various activities. Licorice should contain at least 0.7% of liquiritigenin (C₁₅H₁₂O₄: 256.27, LQ) and 2.5% or more of glycyrrhizic acid (C₄₂H₆₂0₁₆: 822.93, GA) as marker compounds in the Korea Pharmacopoeia (KP), for which the current KP methods are reflux extraction for LQ (2 M HCl/90^oC/1 hr and CH₂Cl₂/40^oC/0.5 hr) and ultrasonic extraction for GA (70% EtOH, 1 hr, 2 times), respectively. This work aimed at providing an alternative method for the fast simultaneous extraction of both quality index constituents, LQ and GA for their HPLC determinations [1]. Microwave-assisted extraction (MAE), which was operated at 150 W for 4 min using 0.5 g of liquorice root powder (less than 5% in moisture, 80 mesh) and 50 mL of different solvents (70% & 100% EtOH, 70% & 100% MeOH, D.W.), was employed to compare its efficacy to that of the conventional KP method, respectively [2, 3]. The results indicated that MAE was more efficient than KP with reduction in extraction time from hours to min [4], as well as simultaneous extraction of both marker compounds with concentrations higher than standard limits of ≥0.7% in LQ and ≥0.25% in GA, respectively when using 100% MeOH solvent.

Fig. 1: HPLC Chromatograms on Liquiritigenin and Glycyrrhizic acid from Licorice powder with different solvents in microwave-assisted extraction (MAE) over conventional method (KP)

Keywords: Liquorice (Glycyrrhizae radix et Rhizoma), liquiritigenin, glycyrrhizic acid, microwave extraction, HPLC.

References:

[1] Pan X, Liu H, Jia G, Shu YY. Microwave-assisted extraction of glycytthizic acid from licorice root. Biochem Eng J 2000; 5: 173 – 177

[2] Korea Food and Drug Administration. Korea Pharmacopoeia. Shinil Books Company, 2008

[3] Zhang QY, Ye M. Chemical analysis of the Chinese herbal medicine Gan-Cao (licorice). J Chromatogr A 2009; 1216: 1954 – 1969

[4] Kwon JH, Bélanger JMR, Paré JJ, Yaylayan VA. Application of microwave-assisted process (MAP) to the fast extraction of ginseng saponins. Food Res Int 2003; 36: 491 – 498