Our tongues can detect odours, study suggests

The tongue does not just detect taste, but might pick up on odours too, according to research shedding new light on how we perceive flavour.

The tongue has long been known to detect whether something tastes sweet, sour, salty, bitter or umami (savouriness) thanks to cells that carry taste receptors, proteins that interact with particular molecules in food.

But now it seems the tongue might have more muscle than previously thought when it comes to determining flavour, with researchers revealing taste cells also bear odour-detecting proteins.

Experts said the findings call into question the idea that the taste of food and its odour are detected separately in the mouth and nose respectively, and only combined in the brain to produce an overall impression of flavour.

Instead, they said, it might be that odour molecules also trigger a response in the mouth, for example by tweaking a taste. However, the team stressed the results do not undermine the importance or role of the nose in picking up aromas.

“I am not saying that [if you] open your mouth, you smell,” said Dr Mehmet Hakan Ozdener of the Monell Chemical Senses Center in Philadelphia, who led the research.

But, he added, the findings open up the possibility of using odours to trick us into healthier eating, for example by adding a very low concentration of an odour to a food to make us think it is sweeter than it is, thereby reducing the need for sugar and helping tackle the obesity. “This is a unique opportunity,” said Ozdener.

Writing in the journal Chemical Senses, Ozdener and colleagues report how they first used genetically modified mice to flag up the location of olfactory receptors, revealing they do indeed turn up on taste cells.

The researchers then turned to human taste cells, finding they contain telltale proteins known to be important in other cells that can detect odours.

The team discovered that human taste cells responded to fragrances, including a clove-scented compound called eugenol, even though the concentration of these substances was below the level necessary to trigger a taste response.

They also found evidence that taste cells might bear both odour and taste receptors that interact with similar molecules, backing up the idea that signals from the receptors might interact.

However, Ozdener said it was not yet clear whether signals from the olfactory receptors get sent directly to the brain, or whether the information is first combined in the mouth.

Prof Johannes Frasnelli from the Université du Québec à Trois-Rivières, who was not involved in the study, said previous research had shown olfactory receptors are not confined to the nose.

“We know that olfactory receptors can be found in many tissues other than the olfactory mucosa and in many cases we do not yet know the function and implications of this,” he said. “For example, olfactory receptors are located on sperm cells; they seem to play a role in guiding the cells to the egg.”

Prof Charles Spence of the University of Oxford also welcomed the research, but said it was too early to talk of using it to tackle obesity.

However, Spence said the research might help to unpick some of the unexplained phenomena around taste, pointing out that previous experiments have found people could still discriminate between foods that are only expected to differ by their odours, even when their nose was not involved.

“There is more to taste than we realised,” he said. “We think it is all very well understood, it’s simple, and yet there are some strange things in there awaiting explanation, and the discovery of this kind of sensitivity might be part of that emerging story.”