New flavour profile? Scientists uncover tongue's sixth basic taste

Researchers have made a groundbreaking discovery, establishing ammonium chloride as a sixth basic taste sensation, alongside sweet, sour, salty, bitter, and umami.

This revelation sheds light on the tongue's ability to detect this distinct taste, primarily found in some Scandinavian candies.

The study, published in the journal Nature Communications, uncovers the underlying mechanisms of this taste perception, which has eluded scientists for decades.

Ammonium chloride taste in Scandinavian candies

The research highlights ammonium chloride's unique taste, a favoured ingredient in certain Scandinavian confections.

Neuroscientist Emily Liman, a co-author of the study from the University of Southern California, told the Independent that residents of Scandinavian countries may already be familiar with and appreciate this taste.

Salt licorice, a popular candy in northern European nations, commonly contains salmiak salt or ammonium chloride.

Tongue's response mechanism

While previous knowledge indicated the tongue's reaction to ammonium chloride, identifying the specific protein receptors responsible had remained elusive.

Recent research had previously uncovered the protein OTOP1, which plays a pivotal role in detecting sour tastes. It functions as a channel for hydrogen ions when exposed to acidic sour foods, like lemonade and vinegar.

Researchers hypothesised that ammonium chloride might also activate OTOP1 due to its impact on hydrogen ion concentration within cells.

Scientists introduced the gene responsible for the OTOP1 receptor into lab-grown human cells, allowing them to produce the OTOP1 receptor.

These cells were then subjected to acid or ammonium chloride exposure, and their responses were meticulously measured.

The study found that ammonium chloride robustly activated the OTOP1 channel, rivalling or surpassing acid's activation levels.

Small quantities of ammonia from ammonium chloride entered the cell, leading to a rise in pH and fewer hydrogen ions.

This pH difference drove an influx of hydrogen ions through OTOP1, detectable through changes in electrical conductivity across the channel.

Taste bud cells from normal mice exhibited a significant increase in action potentials in response to ammonium chloride, while cells lacking OTOP1 showed no such response, confirming OTOP1's role in perceiving ammonium chloride.

Researchers noted that the OTOP1 channel displayed varying sensitivity to ammonium chloride among different species.

This divergence suggests that the ability to taste ammonium chloride may have evolved as an adaptation to avoid consuming potentially harmful substances rich in ammonium.