Inulin reduces production of TMA during fermentation of red meat by the human gut microbiota in vitro

Objective: Certain metabolites produced by the gut microbiota, like the biogenic amine Triethylamine (TMA) appear to increase the risk of cardiovascular disease upon colonic fermentation of choline or L-carnitine. Here, we investigated the ability of the prebiotic inulin to impact gut microbiota protein fermentation and production of potentially toxic metabolites using NMR based metabonomics and in vitro faecal batch cultures. Methods: Fermentation of meat digested using an in vitro digestion process were conducted using 24 h pH-controlled anaerobic batch cultures and fresh faeces from 5 healthy human donors (n=5). For each donor, faecal fermentations of the negative control (no substrate), inulin (1% w/v), beef (0.5% w/v) and beef + inulin (1.5% w/v) were run over 24 h. Cell free supernatant samples taken at 0, 5, 10 and 24 h fermentation were analyzed with proton magnetic resonance spectroscopy (1H-MRS) and multivariate analysis (MVA) to determine the change in metabolite profiles. Fecal microbiota composition is being analyzed by fluorescent in situ hybridization and 16S rRNA community profiling. Results: Metabonomic analysis suggested that inulin improved faecal microbiota protein metabolism, by increasing the consumption of amino acids, such as tryptophan and phenylalanine, but at the same time reducing the production of potentially toxic metabolites including TMA, 5-Aminopentanoate (a precursor of cadaverine) and phenol. Conclusions: In the presence of inulin, fermentation of meat by the gut microbiota was associated with reduced production of toxic metabolites. This supports the notion that increased consumption of fermentable fiber or prebiotics like inulin may be one means of reducing the production of harmful metabolites by the gut microbiota.