Smelling with your tongue? Olfactory receptors for detecting odors present in tongue cells

26 Apr 2019 --- Functional olfactory receptors, the sensors that detect odors in the nose, are also present in human taste cells found on the tongue, according to new findings from research at the Monell Chemical Senses Center in Philadelphia, US. The study was published online on Oxford Academic, ahead of print in Chemical Senses. This latest discovery suggests that interactions between the senses of smell and taste may begin in the tongue and not the brain, as previously thought, highlighting an opportunity of formulating healthier food and beverages for future industry applications.

“This research opens new research avenues on exploration of interaction and modulation between odor and taste sensation,” senior author and cell biologist at Monell, Dr. Mehmet Hakan Ozdener, tells FoodIngredientsFirst. 

“Flavor modulated taste sensation at the taste cell level is critically important for the perception and recognition of taste molecules, therefore the understanding the interaction of each ingredient molecules at cellular level with the different sensory receptors would help food and beverage industry,” he explains.

While most people will equate flavor with the sense of taste, findings from this latest study demonstrate that the distinctive flavor of most foods and drinks arises from smell. With this knowledge, the industry may look towards reformulating products to suit demands for healthier selections. “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,” says Dr. Ozdener.

Even preceding this discovery, industry players have been experimenting with scent as a mode of enhancing flavor experiences. In October 2018, SZENT announced the launch of its flagship product lineup – bottled water, equipped with the brand’s proprietary scent ring infused with all-natural oils, which channels the flavor experience through the user’s sense of smell, avoiding the need for artificial sweeteners or additives.

A single taste cell can contain both taste and olfactory receptors
Until now, taste and smell were considered to be independent sensory systems that did not interact until their respective information reached the brain. Taste, which is the sense that detects sweet, salty, sour, bitter and umami (savory) molecules on the tongue, evolved as a survival instinct to assess the nutrient value and potential toxicity of what we put in our mouths. Smell provides detailed information about the qualities of food flavors (i.e., “Is this banana, licorice, or cherry?”). The combination of inputs from taste, smell and other senses creates the multi-modal sensation of flavor.

In the study, 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.

Subsequently, the research team used a method known as calcium imaging to analyze the way in which the cultured taste cells responded to odor molecules in a manner similar to olfactory receptor cells.

Together, the findings from both study segments provide 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. Additionally, it was confirmed 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 odor and taste stimuli on the tongue,” says Dr. Ozdener.

In addition to providing insight into the nature and mechanisms of smell and taste interactions, the findings also may provide a tool to increase understanding of how the olfactory system detects odors. Scientists have yet to uncover which molecules activate the vast majority of the 400 different types of functional human olfactory receptors and because the cultured taste cells respond to odors, the researchers say they could potentially be used as screening assays to help distinguish these unidentified molecules.

Moving forward, the scientists will seek to determine whether olfactory receptors are preferentially located on a specific taste cell type (i.e., sweet- or salt-detecting cells). Other future studies will further explore how odor molecules modify taste cell responses and ultimately, human taste perception.

By Benjamin Ferrer