Bioavailability of intact proanthocyanidins in the rat colon after ingestion of grape seed extract.

Current evidence shows that monomeric flavonoids are known to be only slightly absorbed in the small intestine, but the metabolism of oligomeric and polymeric proanthocyanidins (PAC) in the colon is poorly understood. The objective of this study was to optimize the analysis of grape seed extract (GSE) in feces and use that method to assess the presence of PAC in the colon after ingestion of GSE. Rats were fed a diet ad libitum containing 0.25% (w/w) GSE for 10 days. Feces were collected daily and colonic contents at sacrifice on day 10, respectively. The recovery of fecal PAC using a solid-phase extraction (SPE) method was >70%. PAC were separated by normal-phase HPLC with fluorescence detection, and subsequent peak confirmation was done by MS-ion trap. The concentration of colonic contents at day 10 was 13.9 mg/kg for monomer, and those for oligomers (dimers-hexamers) were 33.4, 84.6, 87.2, 57.3, and 35.7 mg/kg, respectively. The concentration of monomeric and oligomeric PAC in daily feces was similar among days. In the mass balance analysis, approximately 11% of ingested PAC was recovered in the feces. These findings indicate that ingested PAC were present in the colon as the intact parent compounds and thus may contribute to the health of the gastrointestinal tract.