Effects of Post-harvest Storage and Drying Temperatures on Four Medicinal Compounds in the Root of Chinese Licorice (Glycyrrhiza uralensis)

The root of Chinese licorice (Glycyrrhiza uralensis) is used worldwide as a medicinal herb. The goal of this study was to understand changes in the concentrations and compositions of four medicinal compounds—glycyrrhizic acid (GL), liquiritin (LQ), liquiritigenin (LG), and isoliquiritigenin (ISLG)—in the root of Chinese licorice during post-harvest treatment. The effects of post-harvest storage temperatures (−80, −30, −13, 4, and 25°C) and drying temperatures (30, 40, 50, and 60°C) on concentrations of the four medicinal compounds were investigated. GL and LQ concentrations in roots stored at −30 and −13°C for 1–2 weeks tended to be 4% to 13% higher than GL and LQ concentrations in roots dried directly in a vacuum freeze dryer (controls). LG concentrations in roots stored at 4°C for 2 weeks were nearly 60-fold higher and ISLG concentrations at 25°C for 1 week were 10-fold higher than LG and ISLG concentrations in the controls. In addition, low temperature (30 and 40°C) drying compared to vacuum freeze drying (controls) increased LG and ISLG concentrations without decreasing GL and LQ concentrations. This study provided an approach to increase the target compound concentrations in Chinese licorice for different market demands (drugs, cosmetics, and food).