The role of human gut bacteria in bioactivation of polyphenolic isoflavones and pyranoanthocyanins

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Plant-derived flavonoids and other polyphenols are proposed to have beneficial effects on human health. The intestinal microbiota may play a key role in the conversion of polyphenolic compounds following their intake with food and dietary supplements. Bacteria present in the human gut have been shown to catalyze not only the deglycosylation and deconjugation of polyphenolics but also the transformation of the resulting aglycones. The bacterial metabolites thereby formed may have biological activities that differ from those of the parent compounds. The project aims to elucidate the role of human gut bacteria in the bioactivation of selected isoflavones and pyranoanthocyanins ingested with diet. Of the isoflavones, daidzein is known to be activated to equol exclusively by intestinal bacteria. Equol-forming strains will be isolated and their activity verified in vivo using a gnotobiotic rat model. Whereas daidzein is known to be released from O-glycosides in the human gut, its formation from C-glycosides still needs to be demonstrated. Thus, the relevance of bacterial daidzein formation from its 8-C-glucoside, puerarin, will be clarified by in vitro fermentation experiments. Similarly, the O-deglycosylating activity of gut bacteria may result in bioactivation of pyranoanthocyanins. To test this hypothesis, members of these anthocyanin-derived pigments, such as pinotin A, will be included in studies relating to bacterial deglycosylation and further conversion. The data obtained within the project will contribute to the benefit/risk assessment of the tested polyphenols.