Determination of Flavonoids in Licorice Using Acid Hydrolysis and Reversed-Phase HPLC and Evaluation of the Chemical Quality of Cultivated Licorice

Licorice contains flavonoids and triterpenoids as the major bioactive components. Most of the flavonoids are the glycosidic form of liquiritigenin (LIQ), isoliquiritigenin (ISO) and formononetin (FOR). A reversed-phase HPLC method for the quantification of LIQ, ISO and FOR in licorice was developed. This method does not measure each glycoside but measures the aglycones using acid hydrolysis. All calibration curves showed good linear regression (r > 0.9998). The method showed good precision for intraday (RSD < 2.14%) and interday (RSD < 0.51%) assays. The limit of detection was 0.031 mu g for LIQ, 0.011 mu g for ISO and 0.006 mu g for FOR. The limit of quantification was 0.31 mu g for LIQ, 0.11 mu g for ISO and 0.06 mu g for FOR. The flavonoid contents along with the glycyrrhizin content of cultivated licorice from seedling plants in Japan and commercial wild licorice were investigated. This new method could be extremely useful for evaluating the quality of licorice.