The Taste of Fermentation: Propionic Acid Is Judged More Pleasant Than Other Short Chain Fatty Acids

Short chain fatty acids (SCFAs), such as acetic, propionic and butyric acids have many health benefits, but they have been almost exclusively studied in the context of the gut, where they are produced as by-products of the gut microbiome. SCFAs, however, are also found in fermented foods as metabolites of beneficial microbes, and may signal to taste centers of the brain that these healthful bacteria are present and, if consumed, can colonize the gut and promote health. Two free fatty acid receptors (FFARs), FFAR2 and FFAR3, have been identified in taste tissue and have different binding affinities for SCFAs based on their carbon chain length, though both bind propionic acid. Our objective was to assess whether propionic acid is preferred over the other SCFAs. With nose clips on, 10 participants tasted five samples of a mildly sweet solution (200 mM glucose) mixed with (1) 20 mM acetic acid, (2) 20 mM propionic acid, (3) 20 mM butyric acid, (4) citric acid matched for sourness, or (5) the glucose solution neat. Participants ranked the five samples by preference, and then repeated the ranking without nose clips. All tests were done in duplicate. Participants ranked the glucose + propionic acid as highly as the glucose + citric acid and the glucose neat solutions both with and without nose clips unlike the other SCFAs. These results suggest that humans show preference for the taste of propionic acid, a metabolic by-product of fermentation. The observation indicates that the ingestion of health-promoting fermented foods may have been a positive evolutionary pressure resulting in short-chain fatty acid receptors in taste tissue. Future research will focus on identifying the receptors and signaling pathways involved in the taste detection of and preference for SCFAs in foods. This research was supported by NIH DC014286 and USDA HATCHNJ14120 to PASB.