Sixth 'Taste' Discovered - Calcium
Here's the new taste sensation — your tongue might be able to taste calcium.
The capability to taste calcium has now been discovered in mice. With these rodents and humans sharing many of the same genes, the new finding suggests that people might also have such a taste.
The four tastes we are most familiar with are sweet, sour, salty and bitter. Recently scientists have discovered tongue molecules called receptors that detect a fifth distinct taste — "umami," or savory.
"But why stop there?" asked researcher Michael Tordoff, a behavioral geneticist at the Monell Chemical Senses Center in Philadelphia. "My group has been investigating what we believe is another taste quality — calcium."
So assuming the human palate can detect calcium, what does the mineral taste like?
"Calcium tastes calcium-y," Tordoff said. "There isn't a better word for it. It is bitter, perhaps even a little sour. But it's much more because there are actual receptors for calcium, not just bitter or sour compounds."
One way we might regularly perceive calcium is when it comes to minute levels found in drinking water.
"In tap water, it's fairly pleasant," Tordoff said. "But at levels much above that, the taste becomes increasingly bad."
There may be a strong link between the bitterness of certain vegetables and their calcium level. High-calcium vegetables include collard greens, bok choy, kale and bitter melon. One reason some people might avoid these veggies, Tordoff suggests, is because of their calcium taste.
Ironically, while milk and other dairy products are loaded with calcium, the mineral tends to bind to fats and proteins, which prevents you from tasting it in these foods.
A taste receptor designed specifically for calcium makes sense for our survival, since the mineral is key to cell biology and good bones. Low calcium intakes have been implicated in several chronic diseases in people, including osteoporosis, obesity and hypertension.
"Many animals have a specific calcium appetite, which implies they can detect the mineral and consume sufficient quantities of it to meet their needs," Tordoff said.
To investigate how this calcium appetite worked, Tordoff and his colleagues gave 40 different strains of mice a choice between water and a calcium solution to drink.
"Most mice dislike calcium, but we found a very unusual strain that drinks it avidly," Tordoff said. "The PWK strain drank about four times more calcium than water."
By analyzing the DNA of this unusual strain, the researchers were able to identify two genes linked with consuming calcium.
One is a gene for a calcium-sensing receptor called CaSR, which has been found by other researchers in the kidney, brain and gut.
"We didn't know it was on the tongue before," Tordoff said.
The other is a gene known as Tas1r3. This is a component of the "sweet-taste" receptor — a finding that researchers described as "very unexpected."
By measuring the electrical activity of nerves linking the brain and tongue in mice, "we can now say with some certainty that calcium is tasted," Tordoff said.
While it remains to be seen if this discovery in mice also holds true for humans, "there are some tantalizing reports that suggest it does," Tordoff said. "We know people have the sweet-taste gene, Tas1r3, and the gene involved with the calcium-sensing receptor, CaSR. We don't know if we have the same forms of genes as the mice have, but it seems pretty likely they have the same function."
Confirming the existence of calcium taste receptors in people will require scientists to look at fresh human tongues. Tordoff said, tongue in cheek, that "hopefully we won't have to be sitting by as somebody dies to wait to chop their tongues off — we're not ambulance chasers. There are cases where people have cancer of the tongue and have to get them removed."
If calcium taste receptors are found in people, future research could then investigate whether it is possible to bypass these molecules, Tordoff told LiveScience.
"People don't consume as much calcium as nutritionists would like, and one reason for this is that foods high in calcium don't taste good to many people," Tordoff said. "Tweaking its taste could encourage a calcium-deficient population to consume more of this key nutrient."
Tordoff and his colleagues detailed their findings Aug. 20 at the national meeting of the American Chemical Society in Philadelphia.
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