Resumen del póster presentado a la VI International Conference on Polyphenols and Health celebrada en Buenos Aires (Argentina) del 16 al 19 de octubre de 2013.Proanthocyanidin structure features (i.e, interflavanic bond A- or B-type) seems to influence their biological activity. Among others, A-type proanthocyanidins have proven to inhibit the adhesion of pathogenic bacteria to uroepithelial cells of the urinary tract, a property not found for B-type proanthocyanidins. Scientific evidence indicates that the physiological effects of proanthocyanidins could be due to the metabolites formed in the tissues and, mainly, by the colon microbiota during their passage through the gastrointestinal tract. On the other hand, proanthocyanidins and/or their microbial-derived metabolites could exert a selective effect on inhibition or stimulation on the intestinal microbiota that, in turn, would affect microbial metabolizing capacity. The aim of this study was to explore differences in colonic catabolism between A- and B-type proanthocyanidins, by means of experiments in mice fed with cranberry (rich in type-A proanthocyanidins) and grape seed (rich in type-A proanthocyanidins) extracts. After a 3-week adaptation time, JAXc3H/OuJ female mice (n=30) were divided into three groups and maintained in a specific diet (control, 1% cranberry extract and 1% grape seed extract) for 4 weeks. Faecal samples were collected at 5 different times and analysing for phenolic metabolites by UPLC-ESI-MS/MS and for microbial counting of Lactobacillus, Bifidobacterium, Enterobacteria, Clostridiumgroups and Escherichiacoli species. Results indicated differences in the metabolism of A-type and B-type proanthocyanidins related to changes in some microbial groups.Peer reviewe