This project aims to elucidate the effect of pea seed coat fractions on the gut microbiota in more detail to establish the role microbiota play in anti-diabetic effects.
The consumption of peas has been shown to improve glucose tolerance and reduce the adverse effects of type 2 diabetes, although through largely unknown mechanisms. One plausible mechanism is through the modification of microbial populations and activity in the gastrointestinal tract, which can support improved intestinal health and reduced gut permeability. In this project we looked to determine whether peas improve intestinal integrity through modifications of the microbiome, and whether benefits were cultivar dependent. This was done by feeding seed coats from different pea cultivars that varied in polyphenol content as well as the effect of processing with hydrolysis to liberate anthocyanidin monomers from proanthocyanidin chains, and subsequently challenging with an in?estinal pathogen. Experiments were performed in rats and mice in the context of a high fat diet challenge as well as a low fat diet. In addition to in vivo studies, direct antimicrobial activity and enzyme inhibition was tested in vitro. The key findings of the study are that peas have a substantial effect on the composition and activity of the microbiome, and that the effects differ between pea cultivars dependent on their proanthocyanidin content. We found that peas that contained proanthocyanidins had the most striking effects on the microbiome, with substantial depletion of subsets of the microbial population. Consistent with our in vivo findings, microbes that were substantially reduced by the inclusion of peas containing proanthocyanidins were also highly sensitive in the in vitro assays. These results indicated that pea proanthocyanidins modify the microbiome through direct antimicrobial activity. For peas that did not contain substantial proanthocyanidins, we found that microbial short chain fatty acid (SCFA) production was enhanced in both rats and mice, and that these effects could be associated with improved metabolic outcomes. Counter to our original hypothesis, peas that contained substantial amounts of proanthocyanidins reduced SCFA production and increased susceptibility to infection. However, these negative effects on SCFA production and infection susceptibility disappeared if the seed coats were hydrolyzed. Additionally, hydrolyzed peas containing proanthocyanidins had the strongest benefit by reducing weight gain when mice were challenged with a high fat diet, but did not adversely affect growth on a low fat diet. Overall, this research is highly supportive of the use of peas in improving health outcomes, but highlights the need for processing of peas with high proanthocyanidin content. Furthermore, pea cultivars could be selected to support personalized nutrition based on their microbial modifying properties. This work also identifies the potential for the development of antimicrobial treatments using pea proanthocyanidin extracts.