Tip of the Tongue: The 7 (Other) Flavors Humans May Taste
For all our sophistication in the kitchen, the scientific understanding of how we taste food could still use some time in the oven. Dating back to ancient Greece and China, the sensation of taste has historically been described as a combination of a handful of distinct perceptions. Western food research, for example, has long been dominated by the four “basic tastes” of sweet, bitter, sour and salty.
Our ability to sense the five accepted categories comes from receptors on our taste buds. These tiny sensory organs appear mostly on the tongue, the roof of the mouth and in the back of the throat.
In the mouth itself, though, food scientists continue to discover new receptors and new pathways for gustatory impressions to reach our brain. Here are some taste sensations vying for a place at the table as a sixth basic taste.
The element calcium is critical in our bodies for muscle contraction, cellular communication and bone growth. Being able to sense it in our chow, therefore, would seem like a handy tool for survival.
Calcium clearly has a taste, however, and counterintuitively most mice (and humans) don’t like it. People have described it as sort of bitter and chalky – even at very low concentrations. Tordoff thinks our calcium taste might actually exist to avoid consuming too much of it.
An over-sensitivity to calcium-rich foods such as spinach could help explain why four out of five Americans don’t get enough calcium. “There is a strong relation between people not liking vegetables and calcium,” said Tordoff.
That calcium receptor might also have something to do with an unrelated sixth-taste candidate called kokumi, which translates as “mouthfulness” and “heartiness.” Kokumi has been promulgated by researchers from the same Japanese food company, Ajinomoto, who helped convince the taste world of the fifth basic taste, umami, a decade ago.
Spicy-food lovers delight in that burn they feel on their tongues from peppers. Some Asian cultures consider this sensation a basic taste, known in English as piquance (from a French word). Historically, however, food scientists have not classified this undeniable oral sensation as a taste.
That’s because certain piquant compounds, such as capsaicin from peppers, directly activate our tongue’s touch, rather than taste-bud, receptors. The key piquancy receptor is called TRPV1, and it acts as a “molecular thermometer,” said John E. Hayes, a professor of food science at Penn State.
Normally, nerves with this receptor send a signal of hotness to the brain when exposed to substances around 107.6 degrees Fahrenheit (42 degrees Celsius), the heat pain threshold for humans. Capsaicin fits into this the TRPV1 receptor and lowers the activation temperature to 95 degrees Fahrenheit (35 degrees Celsius) – cooler than body temperature.
Hence, “all of a sudden the receptor is sending signals to brain about ‘oh, hot!’” said Hayes, though the food itself is not necessarily hot temperature-wise. These TRPV1 receptors appear all over the body, which is why exposed mucous membranes in the nose or the eyes also feel the burn of pepper spray, for example.
At the opposite end of taste sensation from piquance’s peppers is that minty and fresh sensation from peppermint or menthol. The same trick of sensory perception is at work here – activated touch receptors, called TPRM8 in this case, fool the brain into sensing coldness at normal oral temperatures, said Hayes.
Yet another controversial “taste” is our registering of metals, such as gold and silver, in the oral cavity. Some Asian cultures place gold and silver leaf, as it’s called, atop curry dishes and candies, while Europeans fancy a bit of these metallic foils on pastries. The silver foil garnish is known as “vark” when used on Indian sweets, as in the picture.
The jury is still out on whether our tongues can taste fat, or just feel its creamy texture. Clearly, many of us enjoy fatty foods, from well-marbled steak to pretty much fried anything.
“Fat is a tremendous source of calories,” said Linda Bartoshuk, a physiological psychologist at the University of Florida “Eating fat is encouraged by our brains to have us survive.”
1. Carbon Dioxide
Yet another strong sixth taste candidate: carbon dioxide (CO2). When dissolved in liquids, this gas gives soda, beer, champagne and other carbonated beverages their zingy fizz. [Infographic: All About Champagne]
That familiar tingling was thought to result from bubbles bursting on the tongue, and had therefore been consigned to the touch category. “It’s tricky because CO2 was always considered a trigeminal stimulus,” said Tordoff.
Thus, for those celebrating this New Year’s with a traditional glass of champagne, take delight in the range of tastes – whether official or not – that our tongues and brains affords us.