The findings add to the fast-accumulating body of knowledge on how tastes are perceived, including salty, sweet, bitter, sour and umami (or savory) taste perception. But the authors of this latest research say that there is emerging evidence suggesting that people could be capable of distinguishing other flavors, such as fat or metallic tastes. Entitled "The Taste of Carbonation", the study has been published in the journal Science by researchers from the National Institutes of Health (NIH), and their colleagues from the University of California, San Diego.
They describe an enzyme – carbonic anhydrase 4 – responsible for sensing the taste of carbonation, “tethered like a small flag from the surface of sour-sensing cells in taste buds”. They write that it is this enzyme that interacts with the carbon dioxide in the drink, activates the sour cells, and sends a signal to the brain.
Senior author of the study and scientist at the NIH’s National Institute of Dental and Craniofacial Research Nicholas Ryba said: “Of course, this raises the question of why carbonation doesn’t just taste sour.”
He explained that carbon dioxide also stimulates the mouth’s somatosensory system, whichis responsible for sensations such as touch, temperature and pain. Therefore, the perception of carbonation reflects a combination of somatosensory information and taste information.
Ryba said: "When people drink soft drinks, they think that they are detecting the bubbles bursting on their tongue," he said. "But if you drink a carbonated drink in a pressure chamber, which prevents the bubbles from bursting, it turns out the sensation is actually the same. What people taste when they detect the fizz and tingle on their tongue is a combination of the activation of the taste receptor and the somatosensory cells. That's what gives carbonation its characteristic sensation."
The scientists found that if they inhibited or removed the carbonic anhydrase 4 enzyme from sour-sensing cells in mice – who perceive taste in a similar way to humans – it “severely reduced” their ability to taste carbonation.
However, the researchers said they do not know whether being able to perceive carbonation plays any important role.
"That question remains very much open and is a good one to pursue in the future," said Ryba.
(2009) Vol.326, pp. 443-445
"The Taste of Carbonation"
Authors: Jayaram Chandrashekar, David Yarmolinsky, Lars von Buchholtz, Martyn Goulding, William Sly, Nicholas J. P. Ryba, and Charles S. Zuker.