Conversion of dehydrodiferulic acids by human intestinal microbiota.

Plant cell wall associated dehydrodiferulic acids (DFA) are abundant components of cereal insoluble dietary fibers ingested by humans. The ability of human intestinal microbiota to convert DFA was studied in vitro by incubating 8-O-4- and 5-5-coupled DFA with fecal suspensions. 8-O-4-DFA was completely degraded by the intestinal microbiota of the majority of donors, yielding homovanillic acid, 3-(3,4-dihydroxyphenyl)propionic acid, and 3,4-dihydroxyphenylacetic acid as the main metabolites. The transient formation of ferulic acid and presumably 3-(3-hydroxy-4-methoxyphenyl)pyruvic acid suggests an initial cleavage of the ether bond. In contrast to 8-O-4-DFA, the 5-5-coupled DFA was not cleaved into monomers by any of the fecal suspensions. Only the side chains were hydrogenated and the methoxy groups were demethylated. The cleavage of DFA by human intestinal microbiota, which depended on their coupling type, may affect both the bioavailability of DFA and the degradability of DFA-coupled fiber in the gut.