Procyanidin B2 catabolism by human fecal microflora: partial characterization of 'dimeric' intermediates.

The catabolism by human fecal microflora of pure procyanidin B2 ((-)-epicatechin-4beta-->8-(-)-epicatechin) has been investigated using a static in vitro culture model. For the first time, 24 catabolites were detected by LC-MS(n) with M(r) greater than 290 indicating that they could not have formed from just one of the epicatechin units in the procyanidin structure. Structures have been assigned on the basis of the fragmentation in the ion trap mass spectrometer and with regard to catabolic pathways known to occur in fecal microorganisms. Twenty of these 'dimeric' catabolites produced fragment ions characteristic of flavanols and/or proanthocyanidins. One catabolite was identified tentatively as either 6- or 8-hydroxy-procyanidin B2. Thirteen were characterized as having been microbially reduced in at least one of the epicatechin units. Five contained an apparently unmodified epicatechin unit but in at least one case this was shown to consist of the B-ring of the "upper" epicatechin unit and the A-ring of the "lower". These 'dimeric' catabolites were detected up to 9h after the start of the incubation and collectively accounted for approximately 20% of the substrate.