Identification of microbial metabolites derived from in vitro fecal fermentation of different polyphenolic food sources.

OBJECTIVE: The biological effects of dietary polyphenols are linked to their bioavailability and catabolism in humans. The colon, with its symbiotic microbiota, is an active site where complex polyphenolic compounds are possibly modified to smaller and more absorbable molecules. The aim of this study was to identify the major metabolites derived from microbial colonic fermentation of some common polyphenol-rich foods. METHODS: An in vitro fecal fermentation model was applied to 16 polyphenol-rich foods and polyphenolic precursors. Phenolic metabolites were identified by high-performance liquid chromatography coupled with tandem mass spectrometric detection. RESULTS: Twenty-four phenolic fermentation metabolites were characterized. Some metabolites were common to several polyphenol-rich foods, whereas others were characteristic of specific sources. CONCLUSION: The metabolites identified in vitro likely are generated in the human colon after consumption of polyphenol-rich foods. Their occurrence in plasma and/or urine should be considered when evaluating the bioavailability of polyphenols from specific food groups in humans and in the definition of markers of exposure to specific foods or food groups in epidemiologic studies. However, the search for these and other microbial metabolites after a feeding study in vivo should consider their possible further conjugation at the level of the liver.

Bioavailability of catechins from ready-to-drink tea.

OBJECTIVE: Because consumption of teas may be associated with potential health benefits due to its content in polyphenols and in Western countries the consumption of tea is equally divided between the hot and the ready-to-drink (RTD) cold versions of this typical beverage, the aim of this work was to study the absorption and metabolism of flavan-3-ols in human volunteers after the ingestion of a commercial RTD tea. METHODS: A feeding study was carried out in 20 healthy human volunteers and urine samples were collected for 24h after tea ingestion. Flavan-3-ols-derived molecules were identified and quantified in urine samples by high-performance liquid chromatography with tandem mass spectrometric detection. RESULTS: Eight relevant metabolites were identified in urine, all modified flavan-3-ols with the exception of unmetabolized gallic acid. The urinary excretion of flavan-3-ols was equal to 7.2% of the intake with tea. Gallic acid, which was abundant in the RTD tea used in this study, reached a 4.5% of the drunken amount. CONCLUSIONS: The bioavailability values observed are in agreement with previous reports, although the dosage of polyphenols ingested in this study is remarkably lower. Moreover, the use of a group of 20 volunteers, more than the average number of subjects used for usual human acute-feeding studies involving polyphenols, provides additional credibility to the results. After drinking the RTD ice tea used in this study, the internal compartments are exposed to non-marginal doses of flavanols and flavanol metabolites up to 24h.