Scientists discover evidence of 6th taste
By Carl Samson
A group of scientists led by researchers at the University of Southern California’s Dornsife College has published evidence pointing to a sixth basic taste.
What they discovered: The scientists found that the tongue responds to ammonium chloride through OTOP1, the same protein that detects sour taste. They cited salt licorice — a type of candy common in Scandinavian countries — as an example of food containing ammonium chloride.
“If you live in a Scandinavian country, you will be familiar with and may like this taste,” said USC Dornsife neuroscientist Emily Liman, who led the study.
What they worked with: After identifying OTOP1 in their previous research, the team hypothesized that the protein might also respond to ammonium chloride. Upon testing with lab-grown human cells, they found that ammonium chloride can activate OTOP1 receptors as effectively as or even better than acids.
Released ammonia moves inside the cell and raises the pH level, making it more alkaline. “This pH difference drives a proton influx through the OTOP1 channel,” said Ziyu Liang, first author of the study.
Further tests with mice showed that those genetically engineered to not produce OTOP1 drank water containing ammonium chloride with no issue. Meanwhile, normal mice were repulsed.
Possible evolutionary protection: Ammonium is somewhat toxic, the researchers said. They believe the ability to taste ammonium chloride has evolved to help organisms identify harmful substances.
“Ammonium is found in waste products — think of fertilizer — and is somewhat toxic,” Liman said. “So it makes sense we evolved taste mechanisms to detect it.”
The team also found that sensitivity to ammonium chloride varies among species, likely due to environmental differences. Chicken OTOP1, for one, is more sensitive to the compound than that of zebra fish — possibly because chicken coops are often filled with ammonium that should be avoided, Liman said.
What’s next: The scientists plan to conduct further research to determine whether ammonium sensitivity is conserved among other members of the OTOP proton family. For now, their findings show that ammonium chloride makes a candidate for the sixth basic taste, joining sweet, sour, salty, bitter and umami.
The scientists’ findings were published in the journal Nature Communications.
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