Smelling food flavours with your tongue
While many people equate flavour with taste, the distinctive flavour of most foods and drinks comes more from smell than it does from taste.
Scientists from the Monell Center report that functional olfactory receptors, the sensors that detect odours in the nose, are also present in human taste cells found on the tongue. The findings suggest that interactions between the senses of smell and taste, the primary components of food flavour, may begin on the tongue and not in the brain, as previously thought.
“Our research may help explain how odour molecules modulate taste perception,” said senior author Mehmet Hakan Ozdener, MD, PhD, MPH, a cell biologist at Monell. “This may lead to the development of odour-based taste modifiers that can help combat the excess salt, sugar and fat intake associated with diet-related diseases such as obesity and diabetes.”
Taste, which detects sweet, salty, sour, bitter and umami (savoury) molecules on the tongue, evolved as a gatekeeper to evaluate the nutrient value and potential toxicity of what we put in our mouths. Smell provides detailed information about the quality of food flavour — for example, is that banana, licorice or cherry? The brain combines input from taste, smell and other senses to create the multimodal sensation of flavour.
Until now, taste and smell were considered to be independent sensory systems that did not interact until their respective information reached the brain. Ozdener was prompted to challenge this belief when his 12-year-old son asked him if snakes extend their tongues so they can smell.
In the study, published online ahead of print in Chemical Senses, Ozdener and colleagues used methods developed at Monell to maintain living human taste cells in culture. Using genetic and biochemical methods to probe the taste cell cultures, the researchers found that the human taste cells contain many key molecules known to be present in olfactory receptors.
They next used a method known as calcium imaging to show that the cultured taste cells respond to odour molecules in a manner similar to olfactory receptor cells.
Together, the findings provide what is claimed to be the first demonstration of functional olfactory receptors in human taste cells, suggesting that olfactory receptors may play a role in the taste system by interacting with taste receptor cells on the tongue. Supporting this possibility, other experiments by the Monell scientists demonstrated that a single taste cell can contain both taste and olfactory receptors.
“The presence of olfactory receptors and taste receptors in the same cell will provide us with exciting opportunities to study interactions between odour and taste stimuli on the tongue,” said Ozdener.
Moving forward, the scientists will seek to determine whether olfactory receptors are preferentially located on a specific taste cell type, for example, sweet- or salt-detecting cells. Other studies will explore how odour molecules modify taste cell responses and, ultimately, human taste perception.
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