Degradation of Flavonoid Glycosides and Aglycones During in vitro Fermentation with Human Faecal Flora

Using an in vitro fermentation system, human faecal flora metabolism of quercetin-3rhamnoglucoside (rutin), hesperetin-7-rhamnoglucoside (hesperidin), naringenin-7rhamnoglucoside (naringin) and their respective aglycones quercetin, hesperetin, and naringenin were investigated. Substrate degradation and metabolite formation were determined by highperformance liquid chromatography and mass spectrometry. The three flavonoid glycosides were completely metabolized within the 72-h fermentation period, but differences in the degradation patterns were observed. Rutin degradation did not lead to detectable levels of free quercetin, whereas the aglycones of hesperidin and naringin were produced. Considerable amounts of hesperetin were accumulated in the hesperidin substrate within the first 8 fermentation hours. The fermentation of naringin however, led to a linear increase of the aglycone over the whole incubation period. It is concluded from these observations that the flavonoid structure and position of the glycosidic linkage affects the degradation pattern of flavonoid rhamnoglucosides. The metabolites were determined to be phenolic compounds such as hydroxy- and methoxyphenyl acetic and -propionic acids and an aldehyde.