Abstract
Τhe gut microflora metabolism of selected dietary flavan-3-ols was investigated using a static in vitro culture model. Pure procyanidin B2 and its associated monomer, (-)- epicatechin, generated a range of phenolic and phenyl carboxylic acid derivatives. The most abundant were mono- and dihydroxylated phenyl propan-2-ols, mono- and dihydroxylated phenyl valerolactones, a monohydroxylated valeric acid, a monohydroxylated propionic acid and a phenyl acetic acid.
Evidence is presented for the production of novel metabolites, from procyanidin B2, that retain the flavanol A-ring and the C4→C8 interflavan bond, including some of comparatively large mass (Mr ≥ 290) that retain the ‘dimeric’ nature of the substrate. It was confirmed that microbial metabolism favoured dehydroxylation at the position 4’- rather than the 3’-, and that both ɑ- and ß-oxidation occurred.
The in vitro metabolism of (+)-catechin and (-)-epigallocatechin by human faecal microflora produced fewer metabolites than (-)-epicatechin or procyanidin B2. The in vitro metabolism of crude black tea extracts, theaflavins (TFs) and thearubigins (TRs), did not produce detectable microbial metabolites.
Studies using co-cultured cells demonstrated that 3-(3’-hydroxy phenyl) propionic acid was absorbed, similar to, but significantly more slowly (P ≤ 0.05) than ferulic acid. Both compounds were absorbed by passive transcellular transport. The 3-(3’-hydroxy phenyl) propionic acid permeated in its free, unconjugated form, suggesting that is a potentially useful biomarker for examining health promoting effects.
Dosing rats intravenously and orally with [14C] procyanidin B2, pharmacokinetic parameters for the [14C] were established. It was demonstrated that a large fraction of the dose of the parent compound administered orally was degraded to different chemical entities by the gut microflora prior to absorption into the systemic circulation.