Cats have a much more refined sense of taste than previously thought, with new research showing that felines are highly sensitive to bitter flavors.
The discovery could help explain why cats so often turn up their noses at certain foods that may be fortified with bitter-tasting vitamins and minerals. The findings, published in the journal PLOS ONE, also provide intriguing clues on how sense of taste evolved in all mammals, including humans.
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"Cats are known as picky eaters," said Monell Center molecular biologist and study lead author Peihua Jiang. "Now that we know that they can taste different bitters, our work may lead to better formulations of cat food that eliminate the bitter off-taste associated with certain flavors and nutrients."
For the study, Jiang and colleagues examined DNA from domestic cats and identified 12 different genes for cat bitter receptors. The scientists then probed the receptor cells to see if one or more of 25 bitter-tasting chemicals activated them.
The researchers confirmed that at least seven of the identified 12 receptors did indeed have the ability to detect one or more bitter chemicals. It is likely that the other five receptors have this ability too, but that they may respond to bitter compounds not included in this particular study.
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Prior research determined that cats are unable to detect sugars. Other carnivores, such as sea lions and spotted hyenas, also lost their ability to taste sweet things. These mammals might have a heightened ability to detect salty and savory flavors.
Cats also seem to go for calorie-dense foods and foods with different textures, helping to explain why savory cat treats with slightly crunchy exteriors and soft interiors appear to be a universal feline fave.
A long-standing theory has held that the ability to taste bitter flavors evolved to protect humans and other animals from ingesting poisonous plants. That is now being questioned since, aside from the occasional chomping on kitty grass, cats go for meat and not plant products.
"Alternate physiological roles for bitter receptors may be an important driving force molding bitter receptor number and function," co-author Gary Beauchamp said. "For example, recent Monell-related findings show that bitter receptors also are involved in protecting us against internal toxins, including bacteria related to respiratory diseases."
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He added that "bitter taste could exist to minimize intake of toxic compounds from skin and other components of certain prey species, such as invertebrates, reptiles and amphibians."
In the study, the researchers also point out that other mammals have multiple receptors dedicated to tasting bitter flavors. Dogs have 15, ferrets have 14, giant pandas have 16 and polar bears have 13.