Measurement of caffeic and ferulic acid equivalents in plasma after coffee consumption: small intestine and colon are key sites for coffee metabolism

Previous studies on coffee examined absorption of phenolic acids (PA) in the small intestine, but not the contribution of the colon to absorption. Nine healthy volunteers ingested instant soluble coffee (∼335 mg total chlorogenic acids (CGAs)) in water. Blood samples were taken over 12 h, and at 24 h to assess return to baseline. Many previous studies, which used glucuronidase and sulfatase, measured only PA and did not rigorously assess CGAs. To improve this, plasma samples were analyzed after full hydrolysis by chlorogenate esterase, glucuronidase and sulfatase to release aglycone equivalents of PA followed by liquid–liquid extraction and ESI-LC-ESI-MS/MS detection. Ferulic, caffeic and isoferulic acid equivalents appeared rapidly in plasma, peaking at 1–2 h. Dihydrocaffeic and dihydroferulic acids appeared in plasma 6–8 h after ingestion (T_max=8–12 h). Substantial variability in maximum plasma concentration and T_max was also observed between individuals. This study confirms that the small intestine is a significant site for absorption of PA, but shows for the first time that the colon/microflora play the major role in absorption and metabolism of CGAs and PA from coffee.