Exploring in vitro production of colonic microbial metabolites from diverse protein sources using human ileal digesta

We explored the relationship between protein fermentation metabolites and ileal digesta composition, using ileal digesta from ileostomates, who ingested nine different protein sources, incubated in the Simulator of the Human Intestinal Microbial Ecosystem (SHIME®). NH₃, short-chain fatty acids, branched-chain fatty acids (BCFA), H₂S, tryptophan derivatives, and biogenic amines were measured in proximal and distal colon vessels. The relative changes in most metabolites were positively correlated with their amino acid precursors in ileal digesta. In both colon vessels, the relative change of NH₃ was a good predictor for the production of other metabolites. Indole was strongly associated with oxindole, 5-HT, and tryptamine and the sum of Trp metabolites in the distal colon. Per gram ingested protein, zein and whey may produce the highest levels of NH₃ and BCFA in the proximal colon and BCFA in the distal colon, whereas whey and pigeon peas may result in the highest levels of H₂S.