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The carbon dioxide in your favorite soda pop tastes sour to your tongue, thanks to an enzyme that converts CO2 into protons that sour-sensing cells can detect.

That means your Coca Cola isn’t just packed with high-fructose sweetness, but, perhaps counterintuitively, its carbonation delivers a delicious squirt of sour too, according to a new study in mice, published Thursday in the journal Science.

“The same taste cell has all the machinery to turn carbon dioxide into protons and then detect the protons as sour taste stimuli,” said Alexander Bachmanov, who was not involved in the study.

The discovery is of particular interest in the food and beverage world, Bachmanov said, because carbonation has long been recognized as a complex phenomenon for the mouth. Even if the sour-sensing cells signal that the carbonation is sour, there are more elements to the process of actually tasting, say, soda water.

“If you think about carbonation, it has more than one attribute,” he said. “One is sourness, which we perceive, but there is probably also some tactile sensation how the bubbles form and burst, tickling the tongue.”

The researchers, led by longtime taste researcher Charles Zuker, now at Columbia University Medical Center, conducted the study using mice that had been genetically altered to lack sour-sensing cells. They found that such mice could not detect carbon dioxide, as seen in the chart. While the study was carried out with mice, the mechanism is expected to have been preserved in other mammals.

Zuker and his colleagues posed a natural evolutionary question: Why would mammals have developed such an excellent carbon dioxide detector?

“CO2 detection could have evolved as a mechanism to recognize CO2-producing sources — for instance, to avoid fermenting foods,” they wrote.

One happy irony of such a hypothesis is that the very same mechanism that allowed our deep ancestors to recognize and avoid fermentation allows modern humans to intentionally create the fermented beverages beer and champagne.

Or, our carbonation-detecting skills could be an accident. The sour-cell enzymes might be maintaining the pH balance of the taste buds, and the tang of soda water is just fallout.

Accident or adaptation, from sparkling wine to Coca Cola to energy drinks to the carbonated yogurt popular in Iran called doogh, humans love carbonation in its many forms. Though their share of the beverage market might be slipping a bit, the world’s population still spends half its drink money on carbonated quenchers.

Zuker’s company Senomyx develops artificial flavors, and have disclosed that they have a partnership with Coca Cola, among other companies.

via Sour: It’s What Carbonation Tastes Like | Wired Science | Wired.com.

Tags: bachmanov, beverage, carbonation, coke, enzyme, genetics, science, taste