Scientists discover new (disgusting) taste

To the ranks of sweet, salty, sour, bitter and umami, researchers say they are ready to add a sixth taste — and its name is, well, a mouthful: "oleogustus."

Announced in the journal Chemical Senses last month, oleogustus is Latin for "a taste for fat."

"It is a sensation one would get from eating oxidized oil," explains Rick Mattes, a professor of nutrition science at Purdue University and one of the study authors.

Now, as we reported earlier this year, scientists have been trying to make the case for fat as a sixth taste for a while now. To qualify as a primary taste, a flavor needs to have a unique chemical signature and trigger specific receptors on our taste buds. When it comes to fat, scientists know the chemical stimuli (fatty acids), and previous research has shown that people have fat receptors in our mouths. But the definition of a primary taste also requires that people be able to distinguish the taste — which has been a sticking point.

That's partly because when people think of the taste of fat, they tend to conjure its mouthfeel — which is the result of triglycerides, Mattes says. "That gives the richness, the creaminess, viscosity and so on," he tells NPR's Rachel Martin.

Triglycerides are the overwhelming source of fat in our diet, Mattes explains. "But that is not the taste part," he says. "The taste part is when we cleave off part of that triglyceride, the fatty acid part." And once it's been cleaved off, the taste that remains is not exactly pleasant.

Mattes and his colleagues had 28 tasters sample lookalike mixtures with different tastes. They found that more than half of the people in their study were able to distinguish fatty acids from the other tastes.

Found in high concentrations in rancid foods, oleogustus actually operates as a protective mechanism of sorts — offering a warning sign to stop eating whatever it is one is tasting. In this respect, it's a bit like bitterness.

But Mattes is careful to offer a caveat.

"At very low concentrations, it may — we don't know this yet — but it may have exactly the opposite effect, the same way bitter stimuli, if you put it just in a glass of water, almost everybody would say it's unpleasant. But in the right context, bitterness adds to the overall appeal of chocolate, of coffee, of wine, many of the foods that we enjoy."

For the most part, though, oleogustus remains something of a paradox: fatty, but still not delicious. It may be tough to wrap your mind around the idea that fatty acids do not equal fatty goodness, but most in the food industry already have, Mattes says.

"The food industry goes to great lengths to keep concentrations of these fatty acids below detection, because they are unpleasant," he says. Copyright 2019 NPR. To see more, visit https://www.npr.org.