C-ring cleavage metabolites of catechin and epicatechin enhanced antioxidant activities through intestinal microbiota.

• Quantitative analysis of 21 microbial metabolites of (epi)catechin was performed. • The antioxidant activities of 12 metabolites were evaluated. • C-ring opened significantly increased the antioxidant activities of (epi)catechin. • Dehydroxylation at the C-3′ or C-4′ mostly deprived their antioxidant activity. The changes in DPPH radical-scavenging capability of catechin and epicatechin during 24 h incubation with fecal microbiota in vitro and the targeted analysis of the characteristic metabolites by using UPLC-Q-TOF indicated that increase in antioxidant activity was synchronous with the accumulation of C-ring cleavage metabolites. Therefore, C-ring cleavage metabolite, 1-(3′,4′-Dihydroxyphenyl)-3-(2′′,4′′,6′′-trihydroxyphenyl)propan-2-ol (3,4-DHPP-2-ol), was separated from incubation liquid. The antioxidant activities of this metabolite and other 11 metabolites were examined through DPPH and ABTS free radical scavenging capacity and ferric reducing antioxidant capability (FRAC). The results indicated that all metabolites with the structure of 3′,4′-dihydroxylated had high antioxidant activity, especially 3,4-DHPP-2-ol, whose EC 50 was 5.97 μM in DPPH assay, 2 times as high as that of catechin, and 1.8 times as high as that of epicatechin. But the metabolites with the structure of monohydroxylated or unhydroxylated on the benzene ring hardly exhibited antioxidant activity. [ABSTRACT FROM AUTHOR]