Microbial metabolites, but not other phenolics derived from grape seed phenolic extract, are transported through differentiated Caco-2 cell monolayers

► Qualitatively, no change in type/number of GSE compounds following GIT digestion. ► However, monomers were significantly increased after gastric digestion with significant decrease in polymers. ► None of the original GSE phenolic compounds passed the Caco-2 cell monolayer. ► In contrast, the two intestinal microbiota metabolites, passed the Caco-2 cell monolayer.