The flowers from Pueraria, which are called Puerariae Flos, have been used since ancient times for recovery from alcohol intoxication. We elucidated the microbial transformation of the main isoflavones (1, 1a and 2) by using 29 commercially available human intestinal bacterial strains together with the bioactivation of the hepatoprotective activity of their metabolites. Tectoridin (1a), which contains only one glucosyl moiety, was metabolized to its aglycone 1b by various bacterial strains. On the other hand, the metabolism of 1 and 2, which both have disaccharide groups, was limited to specific bacterial strains. The metabolites 1c and 2c obtained from the Peptostreptococcus productus strain were completely different from those produced by the other strains. These metabolites were identified as 6-hydroxygenistein and 6-hydroxybiochanin A, respectively. The glycosides 1, 1a and 2 did not show any hepatoprotective activity, whereas aglycones 1b and 2b showed moderate activity. Furthermore, the hepatoprotective activity of the demethylated metabolites 1c and 2c was extremely potent. Although not all people have P. productus in their gastrointestinal tract, the O-demethylated compounds might become one of the bioactivated metabolites when Puerariae Flos is administered orally.

Intestinal bacteria play an important role for the metabolism of soy isoflavonoids. When soy foods are consumed, the soy isoflavone glucosides are metabolized into their aglycones and the related isoflavonoids by intestinal bacteria. We designed an in vitro microbial metabolic system using 29 commercially available human intestinal bacterial strains and elucidated the metabolism of soy isoflavone glucosides. The strains were classified into three categories, which were 14 facultative anaerobes, 13 obligate anaerobes, and 2 aerobes. Almost all facultative anaerobe strains metabolized soy isoflavone glucosides to their aglycones. The ratio of metabolism from glucoside to aglycone was different in each strain. Contrary to the facultative anaerobes, some of the obligate anaerobes did not metabolize soy isoflavone glucosides at all. Both the aerobic bacteria hardly metabolized soy isoflavone glucosides. The bacterial growth speed might show good correlation to the metabolizing speed of both glucosides. Therefore, the speed of metabolism would be different in each bacterial strain, too.

The Pueraria flowers, Puerariae Flos [Puerariae Lobatae Flos (the flowers of P. lobata) and Puerariae Thomsonii Flos (the flowers of P. thomsonii)], have been used as crude drugs to counteract the overconsumption of alcohol in Japan and China. Both types of Puerariae Flos contain a large amount of isoflavones and saponins. Simultaneous analysis of the total saponin and isoflavone fraction within the flowers has proven difficult thus far; however, profile analysis of saponin and isoflavone levels was attempted in this study by using HPLC coupled to an evaporative light scattering detector (ELSD). A characteristic peak of kakkalide was common in the chromatograms of extracts originating from the flowers of P. lobata, though original habitats were different. Tiny peaks of saponins were also observed in chromatograms of all specimens derived from P. lobata. In the chromatograms of six out of eight extracts of Puerariae Thomsonii Flos originating from Guangdong, China, characteristic twin peaks corresponding to tectorigenin 7-O-xylosylglucoside and tectoridin were observed. The distinctive twin peaks were not found in the chromatograms of the extracts produced in Hunan and Sichuan. Although the amounts of total saponins and isoflavones obtained from Puerariae Lobatae Flos were almost the same, those of Puerariae Thomsonii Flos varied remarkably and were not related to habitat. A good yield of a new isoflavone glycoside was obtained from some specimens of Puerariae Thomsonii Flos; the structure was determined to be 6-hydroxygenistein 6,7-di-O-glucoside.