Writing in the journal Chemical Senses​, the US-based researchers noted that whilst ‘considerable’ data has indicated that fat may be a sixth basic taste​​, evidence demonstrating that the sensation of nonesterified fatty acids (NEFA) - which are the proposed stimuli for ‘fat taste’ – provide a different taste has been lacking until now.

"The taste component of fat is often described as bitter or sour because it is unpleasant, but new evidence reveals fatty acids evoke a unique sensation satisfying another element of the criteria for what constitutes a basic taste, just like sweet, sour, salty, bitter and umami,”​ said Professor Richard Mattes of Purdue University – who led the study.

Using perceptual mapping techniques, the team demonstrated that NEFA have a taste sensation that is distinct from the other basic tastes. However, Mattes warned that the taste of fat should not be confused with the feel of fat, which is often described as creamy or smooth.

"Most of the fat we eat is in the form of triglycerides, which are molecules comprised of three fatty acids,"​ he said. "Triglycerides often impart appealing textures to foods like creaminess. However, triglycerides are not a taste stimulus. Fatty acids that are cleaved off the triglyceride in the food or during chewing in the mouth stimulate the sensation of fat."​

"Fatty taste itself is not pleasant. When concentrations of fatty acids are high in a food it is typically rejected, as would be the case when a food is rancid,”​ Mattes added.

The team proposed that the new taste, which would be the sixth basic taste, should be referred to as ‘oleogustus’.

“By building a lexicon around fat and understanding its identity as a taste, it could help the food industry develop better tasting products,”​ said Mattes.

Fat study

Because there are no familiar words to ask people to use to describe the taste of fat, the 102 study participants were given multiple cups of solutions each containing a compound that tastes salty, sweet, umami, bitter, sour or fatty.

Participants were asked to sort the solutions into groups based on which had similar taste qualities. Odor, texture and appearance were all controlled by the team to ensure they matched.

Mattes and his colleagues revealed that the panellists easily segregated sweet, salty and sour samples, confirming they understood the task.

Initially, the fatty samples were grouped with bitter because bitter is the vernacular descriptor for unpleasant taste sensations.

However, when asked to sort samples including bitter, umami and fatty stimuli, panellists grouped the fatty acids together and separately from the other samples, Mattes said.

“Although some overlap was observed between these NEFA and umami taste, this overlap is likely due to unfamiliarity with umami sensations rather than true similarity,”​ said the authors.

“Shorter chain fatty acids stimulate a sensation similar to sour, but as chain length increases this sensation changes,”​ they added. “Fat taste oral signalling, and the different signals caused by different alkyl chain lengths, may hold implications for food product development, clinical practice, and public health policy.”​

While more testing will need to be done before oleogustus can officially join the taste family, these results could be the first step to fat being recognised as a taste in its own right, the authors said.

Indeed, Mattes and his colleagues are also analysing data from more than a thousand participants in a study related to the genetics of fat taste at the Denver Museum of Nature & Science's Genetics of Taste Lab.

Source: Chemical Senses​

Published online ahead of print, doi: 10.1093/chemse/bjv036​​

“Oleogustus: The Unique Taste of Fat”​

Authors: Cordelia A. Running, Bruce A. Craig, Richard D. Mattes