Smelling with your tongue

Identification of functional olfactory receptors in human taste cells opens doors to new approaches to modify food flavor.

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While numerous individuals compare flavors with taste, the particular kind of most foods and beverages comes more from smell than it does from the taste. Taste, which recognizes sweet, sour, bitter and umami (flavorful) molecules on the tongue, advanced as a gatekeeper to assess the supplement esteem and potential toxicity of what we put in our mouths.

Smell gives definite data about the nature of food flavor, for instance, is that banana, licorice, or cherry? The brain consolidates input from the taste, smell, and other senses to make the multi-modal sensation of flavor.

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 a new study by the Monell Center, scientists have reported that functional olfactory receptors, the sensors that detect odors in the nose, are also present in human taste cells found on the tongue. This is a mindblowing discovery that highlights the interaction between the senses of smell and taste, the primary components of food flavor, may begin on the tongue and not in the brain, as previously thought.

Senior author Mehmet Hakan Ozdener, MD, Ph.D., MPH, a cell biologist at Monell said, “Our research may help explain how odor molecules modulate taste perception. This may lead to the development of odor-based taste modifiers that can help combat the excess salt, sugar, and fat intake associated with diet-related diseases such as obesity and diabetes.”

During the study, scientists 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 then used a method known as calcium imaging to show that the cultured taste cells respond to odor molecules in a manner similar to olfactory receptor cells.

Plus, the discovery offers 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.

Ozdener said, “The presence of olfactory receptors and taste receptors in the same cell will provide us with exciting opportunities to study interactions between odor and taste stimuli on the tongue.”

Scientists still do not know what molecules activate the vast majority of the 400 different types of functional human olfactory receptors. Because the cultured taste cells respond to odors, they potentially could be used as screening assays to help identify which molecules bind to specific human olfactory receptors.

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 odor molecules modify taste cell responses and, ultimately, human taste perception.

The study published online ahead of print in Chemical Senses.