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Pure Appl. Chem., 2002, Vol. 74, No. 7, pp. 1189-1198

Licorice root. A natural sweetener and an important ingredient in Chinese medicine

Isao Kitagawa

School of Pharmaceutical Sciences, Kinki University, 3-4-1 Kowakae, Higashi-osaka, Osaka 577-8502, Japan

Abstract: This paper reviews our investigations on the chemical constituents of several kinds of botanically identified licorice roots, which led to the characterization of 13 then-new glucuronide-saponins named licorice-saponins (A­L), apioglycyrrhizin, and araboglycyrrhizin, together with glycyrrhizin and 18α-glycyrrhizin and also of 49 kinds of phenolic compounds and their glycosides (11 then-new). The restoration-promoting activity of licorice-saponin B2 for CCl4-intoxicated hepatocyte function and the structure­sweetness relationship of saponins were discussed. Biologically interesting, but isolable in minor quantities, several licorice-saponins were favorably synthesized from abundantly available glycyrrhizin. With 15 saponins and 49 phenolic compounds (including their glycosides) at hand, chemical evaluation of licorice root processings was undertaken. It was shown that the cortex contained a rich amount of phenolic compounds, whereas the xylem was rich in phenolic glycosides and the saponins contained were richer in the xylem than in the cortex. It was also found that roasted licorice root contained an increased amount of glycyrrhetic acid monoglucuronide, which was secondarily formed from glycyrrhizin through thermal hydrolysis and was known to taste 5 times sweeter than glycyrrhizin.