At the beginning of the 20th century, Japanese scientist Kimi Ikeda first proposed the use of fresh taste as the fifth basic taste besides sweet, sour, salty, and bitter. About 80 years later (1985), the scientific community officially agreed to his viewpoint. According to a report in the 5th issue of Nature Communications magazine, scientists from the Dornish School of Literature, Arts, and Sciences at the University of Southern California in the United States have discovered evidence for a sixth basic taste, which is called "ammonium chloride". For decades, scientists have recognized that the tongue has a strong response to ammonium chloride, but it is uncertain which receptors are responsible. In recent years, they have discovered that protein OTOP1 is a proton channel that enables cells to detect acidity. They hypothesize that this protein may also react with ammonium chloride as it affects the acid levels in cells. In this study, scientists introduced OTOP1 into human cells cultured in the laboratory and exposed some of them to acid or ammonium chloride. They found that ammonium chloride effectively activated the OTOP1 receptor just like acid. Mouse testing confirmed that mice carrying OTOP1 were able to avoid ingesting ammonium chloride, while mice with OTOP1 removed did not mind the taste. Ammonium and gaseous ammonia (decomposition products of amino acids) are usually toxic to organisms. Many animals have the ability to detect and respond to ammonium or ammonia in the environment. Researchers speculate that the ability to taste ammonium chloride may have evolved to help organisms avoid harmful substances. Researchers also observed differences in the reaction to ammonium chloride among species. For example, the OTOP1 channel of chickens is more sensitive, while zebrafish is less sensitive to ammonium chloride. Researchers plan to further explore the reaction of OTOP1 receptors to ammonium chloride, hoping to reveal more about their evolutionary significance. Although saying that a certain food has a "ammonium chloride" flavor is not a very intuitive way to describe it, perhaps foodies will come up with a better name for it, so that it can one day be added to the list of basic flavors. (Reporter Zhang Jiaxin) (Xinhua News Agency)