Scientists from the University of Southern California have discovered a sixth basic sense the human tongue can feel – ammonium chloride. Their research published in the journal Nature Communications on October 5 suggests that protein receptors on the tongue that help detect the sour taste also respond to ammonium chloride, which is a popular ingredient in some Scandinavian candies.
Salt licorice has been a popular candy in some northern European countries at least since the early 20th century and its ingredients consist of salmiak salt, or ammonium chloride.
The recent research uncovered the protein OTOP1, which plays a vital role in detecting sour tastes. It functions as a channel for hydrogen ions when exposed to acidic sour foods, like lemonade and vinegar. The team hypothesised that ammonium chloride might also activate OTOP1 due to its impact on hydrogen ion concentration within cells.
The research then introduced the gene responsible for the OTOP1 receptor into lab-grown human cells, allowing them to produce the OTOP1 receptor. These cells were then exposed to ammonium chloride exposure. The study found that ammonium chloride strongly activated the OTOP1 channel, leading to a rise in pH and fewer hydrogen ions. This pH difference led to an influx of hydrogen ions through OTOP1, detectable through changes in electrical conductivity across the channel.