Cracking open a cold can of Coke and taking a bubbling swig will have your taste buds dancing—and now scientists know why. A
new study shows that cells in taste buds that respond to sour stimuli also seem to be the ones responsible for tasting the carbonation's fizz [NPR].
The fact that we can taste the carbon dioxide in a fizzing soda has previously puzzled scientists, since the human tongue is usually thought to only sense five flavors—bitter, sweet, salty, sour, and umami (also called savory). However, the new study, published in Science, shows that the sour taste buds have an enzyme that interacts with carbon dioxide, so it's not the bursting bubbles that you taste, it's the C02 itself. The researchers discovered this tricky bit of chemistry by studying mice.
They gave the animals sips of club soda or a little buzz of carbon dioxide gas and recorded how the tongue signaled the sensation to the brain. Both soda and the gas produced similar sensations. But when they tested mice bred to have no sour taste buds, the brain never got its sensory alert. Further probing uncovered the enzyme responsible [AP]. The mechanism should be the same in humans, according to the scientists.
The discovery of a C02-sensing taste bud is not only interesting to soft drink manufacturers, but also to evolutionary biologists. After all, Coca-Cola didn't usher in a new era of carbonated beverages until the late 1800s, so why would our sour-tasting cells have evolved to taste carbon dioxide? The study's authors write,
“CO2 detection could have evolved as a mechanism to recognize CO2-producing sources—for instance, to avoid fermenting foods.”
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 [Wired.com].
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Image: flickr / roland