Scientists have discovered that in addition to detecting sweet, sour, salty, bitter, and umami tastes, the tongue responds to ammonium chloride as a sixth basic taste.
The study was published Thursday in the journal nature communications It has been suggested that protein receptors on the tongue that help detect sour tastes also respond to ammonium chloride, a popular ingredient in some Scandinavian candies.
“If you live in a Scandinavian country, you may be familiar with this flavor and may like it,” says study co-author Emily Lehman, a neuroscientist at the University of Southern California.
Salted licorice has been a popular candy in some Nordic countries since at least the early 20th century, and its ingredients consist of salmiak salt, or ammonium chloride.
Scientists have known that the tongue responds to ammonium chloride in some way, but the specific protein receptors on the tongue that respond to ammonium chloride remain unknown despite decades of extensive research. It wasn’t explained.
Recent research has shed further light on this process, revealing a protein that detects sour taste through a protein receptor on the tongue called OTOP1.
This protein resides within the cell membrane of the tongue and forms channels through which hydrogen ions, an important component of acidic and sour foods, move into the cell.
OTOP1 plays a key role behind other acidic foods, such as lemonade, which is rich in citric and ascorbic acids, and vinegar, which imparts a tangy, sour taste when it hits the tongue.
Because ammonium chloride also affects the concentration of hydrogen ions within cells, the researchers wondered if ammonium chloride could cause OTOP1.
To study this, scientists introduced the gene behind the Otop1 receptor into human cells grown in the lab, allowing the cells to produce the OTOP1 receptor.
The researchers then exposed these cells to acid or ammonium chloride and measured the response.
“We found that ammonium chloride is a very strong activator of the OTOP1 channel. It activates as much or more than acids,” Dr. Lehman said.
It was found that small amounts of ammonia from ammonium chloride migrated within the cell.
Ammonia is alkaline, so it increases the pH and decreases hydrogen ions.
According to the scientists, this pH difference facilitates the influx of hydrogen ions through OTOP1, which could be detected by measuring changes in electrical conductivity across the channel.
To measure this, the scientists used taste bud cells from normal mice and genetically engineered mice that do not produce OTOP1.
They measured how much electrical responses the taste cells produced when ammonium chloride was introduced.
Taste bud cells from normal mice showed a sharp increase in action potentials upon addition of ammonium chloride, whereas taste bud cells from mice lacking OTOP1 were unable to respond to salt.
This confirmed that OTOP1 responds to ammonium chloride.
The scientists also found that mice with functional OTOP1 protein did not find the taste of ammonium chloride appealing and did not drink salt-laced water, whereas mice without the protein did not find the taste of ammonium chloride appealing, even at very high concentrations. I also discovered that I didn’t care about the solution either.
“This was really the clincher. This shows that the OTOP1 channel is essential for the behavioral response to ammonium,” Dr. Lehman said.
The researchers also found that the OTOP1 channel appears to be more sensitive to ammonium chloride in some species than in others.
They suspect that the ability to taste ammonium chloride was an adaptation that helped the organisms avoid ingesting harmful biological substances containing high concentrations of ammonium.
“Ammonium is found in waste products (think fertilizer) and has some degree of toxicity, so it makes sense that we evolved a taste mechanism to detect it,” explains Dr. Lehman. However, he added that more research is needed to understand the differences between species.