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Oleogustus: Fat May Become the Sixth Taste

There's a new flavour in town, and its name is oleogustus—the taste of fat.

For a while now, researchers have been proposing that fat should be the sixth primary taste alongside sour, sweet, bitter, salty and umami (savoury). However, finding enough evidence to classify fat as a distinctive flavour has been the main problem. But recently, new research on how we perceive fatty tastes may be the stepping stone that oleogustus needs in order to be accepted.

What constitutes a primary flavour?

To be considered a basic taste, a flavour must meet five criteria. First, there must be a chemical stimulus, which then activates specific receptors on our taste buds. The chemical signal must travel from the receptors to the brain, and the brain must be able to identify and process the taste. Finally, the entire process has to trigger physiological effects on the rest of the body.

So does fat meet all of these criteria? For the most part, yes. Researchers have determined that the chemical stimuli for fat are fatty acids, which also have receptors in our mouths and intestines. The tricky part though is determining if fat can be specifically perceived by the brain, independent of factors such as aroma, texture and other flavours.    

Leaving an unpleasant aftertaste

When we think about the taste of fat, we often associate it with the creamy texture that comes with it. This texture is caused by triglycerides, which are composed of several fatty acid chains. However, triglycerides are not the main source of taste as they have no effect on our taste buds. It's actually the fatty acids themselves that provide the flavour, and the fatty taste is released after triglycerides are broken down during chewing.

In its true form, fat is considered to be a very unpleasant flavour—similar to the taste of rancid food. Like bitterness and sourness, the unpalatable taste left by oleogustus may act as a protective measure to stop ourselves from eating unsafe and moldy food.

A distinguishing taste test

In a study done by Purdue University, 102 participants were given numerous cups containing mixtures that each tasted sweet, salty, bitter, sour, umami or fatty, and they were asked to group them together based on similar flavours. Texture, odour and appearances were all controlled for.

The participants were able to distinguish sweet, salty and sour flavours with ease, but when it came down to the fatty mixtures, they initially classified them as being bitter due to the unpleasant taste. Later, when they were asked to group together bitter, umami and fatty samples, the participants grouped the fatty flavours together and were able to distinguish them as being separate from the rest. Based on these results, there is growing evidence that fatty acids can be differentiated as a separate flavour.

Can we accept oleogustus as the sixth taste?

While most people have a hard time describing the taste of fat, they're still able to tell that it's different from the basic flavours. However, our conscious perception of oleogustus isn't quite the same. When we eat something salty, we instantly identify it as saltiness, but with fatty acids, we don't have the same instant perception. The brain's ability to perceive fat is still a debatable topic, as more evidence is needed to determine if fat is actually distinct enough by itself.

So far, researchers are going the extra mile by studying the genetics behind the taste of fat. There's still a long way to go, but with the growing evidence that fat is independent from the other primary flavours, oleogustus may soon become the official sixth taste.  
 

Taste is only one of the many senses that our bodies possess. Find out more about the rest of them by checking out Senses on Science World Resources and by visiting our Body Works Gallery!