Flavonoid aglycones, degradation

Lin YT, Hsiu SL, Hou YC, Chen HY, Chao PD. 2003. Degradation of flavonoid aglycones by rabbit, rat and human fecal flora. Biol Pharm Bull 26 747-751. 

Justesen, U., Arrigoni, E., Larsen, B.R., and Amado, R., Degradation of flavonoid glycosides and aglycones during in vitro fermentation with human faecal flora, L bensmitt. Wissensch. Technol, 33, 424, 2000. 

Biliary excretion and enterohepatic circulation ensures that flavonoids are continually subjected to further metabolism and degradation by colonic microflora. Only 50% of a dose of rutin was excreted in the urine after 48 h [61] less than 1% was in the form of its aglycone (quercetin), with the remainder being characterized as phenolic acids. In a recent study involving administration of C-quercetin to human volunteers, Walle et al. [62] showed that up to 81% of the oral dose was recovered as carbon dioxide in a 72-h period only 2-5% was excreted in the faeces, with 3-6% excreted in the urine. These studies demonstrate that quercetin undergoes extensive intestinal, bacterial, and systemic metabolism, resulting in a complex mixture of metabolites with altered bioactivity. 

Gut microflora is known to play a prominent role in the gastrointestinal metabolism of flavonoids. Enzymes released by the resident microbes have the ability to gradually hydrolyze the glycosides into aglycones, which are absorbed by the intestine. The unabsorbed aglycones that pass through the small intestine are degraded by colonic... 

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