Metabolites and Changes in Antioxidant Activity of A-Type and B-Type Proanthocyanidin Dimers after Incubation with Rat Intestinal Microbiota.

Metabolism of B-type EC dimer, A-type EC dimer, A-type ECG dimer, and A-type EGCG dimer was compared in vitro after incubation with rat intestinal microbiota for 0-24 h. A "dimeric" catabolite (m/z 815.6) was detected in four procyanthocyanidin dimers. Although the early cleavage of the C4-C8 interflavan bond and the reductive cleavage of the C-ring occurred in both B-type and A-type dimers, the degradation routes of these two types of dimers might somewhat differ. A dimeric catabolite C1 and more low molecular weight phenolic acids were detected in the metabolites of A-type EC dimer, but not in B-type EC dimer. The antioxidant capabilities of the A-type dimers were enhanced significantly after incubation for 6 h, whereas the antioxidant capacity of B-type EC dimer decreased. The results suggested that changes in antioxidant activity of procyanidin dimers after bioconversion by rat intestinal microbiota were not only structure dependent but also incubation condition dependent.