Impact of flavor enhancers on the structure and function of the intestinal microbiome

Introduction: The human intestinal microbiome plays a vital role in human health and is influenced by both dietary and non-dietary factors. Food additives like monosodium glutamate (MSG) are commonly used in the food industry as taste enhancers; however, their impact on the gut microbiome is still not well understood. Glutamate acts as a signaling molecule in the enteric nervous system, affecting neuroendocrine responses, suggesting that the gut microbiome could also be responsive to MSG.

Goals: Using an in vitro simulator of the human intestinal microbial ecosystem (SHIME®) this study investigated the effects of MSG on the colonic microbiome in a case-control design focusing on transcriptional and metabolic responses.

Materials and Methods: SHIME® is a chemostat system that can simulate the luminal colon region via different bioreactors representing the stomach/small intestine, as well as proximal (PC) and distal colon (DC). The study was conducted using a defined community of eight bacterial strains (SIHUMIx) representing the important gut phyla Firmicutes (Blautia producta, Clostridium butyricum, Clostridium ramosum, Lactobacillus plantarum, Anaerostipes caccae), Bacteroidetes (Bacteroides thetaiotaomicron), Actinobacteria (Bifidobacterium longum), and Proteobacteria (Escherichia coli). We applied MSG in a mixture with a defined medium containing 25% starch at a concentration of 0.5 mg/mL, which was adjusted to pH 2 and then heated by autoclaving.

Results: Over a three-week period (stabilization, treatment, and post-treatment phases), shifts in microbial community composition and gene expression patterns were analyzed. In addition, short-chain fatty acid (SCFA) profiling was performed. As expected, the relative abundance of members of the synthetic communities varied in the different simulated gut compartments. In the proximal colon, B. thetaiotaomicron, L. plantarum, E. coli and C. butyricum were predominant, while the distal colon was dominated by B. thetaiotaomicron, B. producta, E. coli and A. caccae. The application of MSG led to a reduction in the abundance of B. thetaiotaomicron, L. plantarum, and C. butyricum in the proximal colon, as well as a decrease in B. thetaiotaomicron and E. coli, and an increase in B. producta in the distal colon. A reduction in SCFA concentrations was detected across both colon regions. Further findings, including transcriptomic data and detailed results, will be presented in the frame of the poster.