Metabolites in contact with the rat digestive tract after ingestion of a phenolic-rich dietary fiber matrix

Grape antioxidant dietary fiber (GADF) is a phenolic-rich dietary fiber matrix. The aim of this work was to determine which phenolic compounds come into contact with colonic epithelial tissue after the ingestion of GADF. By use of HPLC-ESI-MS/MS techniques phenolic metabolites were detected in feces, cecal content, and colonic tissue from rats. Free (epi)catechin (EC) was detected in all three sources, and more than 20 conjugated metabolites of EC were also detected in feces. Fourteen microbially derived phenolic metabolites were also identified in feces, cecal content, and/or colonic tissue. These results show that during transit along the digestive tract, proanthocyanidin oligomers and polymers are depolymerized into EC units. After ingestion of GADF, free EC and its conjugates, as well as free and conjugated microbially derived phenolic metabolites, come into contact with the intestine epithelium for more than 24 h and may be partly responsible for the positive influence of GADF on gut health.This work was supported by the Spanish Ministry of Education and Science (Research Grants AGL2004-07579-C04-02 and -03; AGL2009-12374-C03-03/ALI; and SAF2008-00164), the Instituto de Salud Carlos III and European Regional Development Fund (ISCIII-RTICC, RD06/0020/0046), the Generalitat de Catalunya (2009SGR1308), 2009CTP 00026 and Icrea Academia award 2010 granted to M. Cascante and the European Commission (Etherpaths Project KBBE-Grant Agreement 222639). J.P.-J. thanks the Spanish Ministry of Science and Innovation for granting her a Sara Borrell postdoctoral contract (CD09/00068).Peer reviewe