That fruit fly hovering over your kitchen counter may be attracted to more than the bananas that are going brown; it may also want a sip of your carbonated water. Fruit flies detect and are attracted to the taste of carbon dioxide dissolved in water, such as water found on rotting fruits containing yeast, concludes a study appearing in the August 30 issue of the journal Nature. Scientists at the University of California, Berkeley, who conducted the study, suggest that the ability to taste carbon dioxide may help a fruit fly scout for food that is nutritious over that which is too ripe and potentially toxic. The research is partly funded by the National Institute on Deafness and Other Communication Disorders (NIDCD), one of the National Institutes of Health.
Fruit flies contain similar versions of many human genes, which is why we study them for a variety of health issues, including taste, says James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. This research raises the question of whether people also may have the ability to taste carbon dioxide and perhaps other chemicals in food. If this were found to be true, our sense of taste could be even more complex than we realize. Currently, scientists recognize five tastes in humans: sweet, salty, bitter, sour, and umami, or savory. Before todays findings, fruit flies were known to be able to taste sweet, bitter, and salty.
The researchers note that a fruit flys attraction for the taste of carbon dioxide is on a much smaller scale than for sugar, so it may be used more as a possible flavor enhancer as opposed to a full-fledged taste. This makes sense, they say, since carbon dioxide offers no nutrition to the fly.
In humans, taste occurs by way of taste cells, sensory cells that are clustered in the taste buds of the mouth, tongue, and throat, and that express certain proteins, called receptors. These receptors are activated by specific chemicalscalled tastantsfound in foods and drinks.
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NIH/National Institute on Deafness and Other Communication Disorders