History and the immunostimulatory effects of heat-processed licorice root products with or without honey

In traditional Chinese medicine, the dried root of Glycyrrhiza uralensis Fisch. (licorice root) is usually used after stir-baked with honey. However, in Japanese traditional Kampo medicine, processed licorice root is prepared by roasting without honey.

We summarized our previous studies on the processed licorice root products to review the effectiveness of the processing for licorice root.

We summarized our previous studies about processed licorice root. The first report was about investigating the successive literatures of traditional medicine in China and Japan about the processing of licorice root. Next was the report about chemically analyzing for prepared various kinds of processed licorice root samples. The last reports were evaluating in vitro effects of the extracts of these samples and heated honey on granulocyte colony-stimulating factor (G-CSF) secretion in cultured intestinal epithelial cells.

Before the Song dynasty in mainland China, the processing of licorice root for the internal usage had been roasted without any drug adjuvants. Then, clinicians had also used honey-roasted licorice to treat throat pain since the Song dynasty, and honey-roasted licorice has been used as the substitute to roasted licorice since the end of the Qing dynasty. While the descriptions using honey have been disappeared in 18th century in Japan. We found that the conversion between liquiritigenin and isoliquiritigenin or between liquiritin and isoliquiritin in licorice root by heating was accelerated by using honey as drug adjuvant. The inducible effect of G-CSF of licorice root was not augmented by roasting, but significantly augmented by stir-baked with honey. Heated honey also had this activity, and isomaltose contributed the appearance of this activity among the constituents in honey. The best activity was appeared when isomaltose was heated at 180 °C for 60 min or at 200 °C for 15-30 min, and the average molecular weight of the active product was 790 kDa.

By our previous studies, we believe that the processing method in China is better than that in Japan for licorice root, since the immunostimulatory effects are appeared in honey used as drug adjuvant when honey is heated. Among the ingredients of honey, isomaltose can be used as the marker compound to choose a conforming honey product for the processing of licorice root.