It is commonly known that there are not just four, but five tastes: salty, sweet, bitter, sour and umami, also referred to as the fifth taste. Most of us learned in school that the distribution of taste buds on the tongue could be depicted as a map. Even though it has been since proven that the so-called “tongue map” is wrong, there is still the widespread misconception that sweetness may be detected at the tip of the tongue, saltiness and sourness on the sides of the tongue, and bitterness at the back of the tongue, near the throat. Umami is often missing from these kind of “maps.”
Scientific studies have shown that each of the thousands of taste buds on our tongues host roughly 100 taste cells that contain specialised receptors for each of the five recognised taste qualities. These findings suggest that the idea of different taste sections coexisting on the tongue is simply untrue. Tastes are therefore not allocated to specific areas of the tongue. Instead, it appears that they may be detected to the same extent all over the tongue, with some areas being more sensitive to certain tastes. While salty and sour taste sensations are both detected through ion channels, sweet, bitter, and umami tastes are detected by other specialised receptors. In 2000, researchers from the University of Miami identified the taste receptor specific to detect umami taste. The amino acid glutamic acid is evoking the distinctive umami taste. Glutamic acid occurs in all foodstuffs that are rich in proteins, as well as those which have been allowed to ferment.
The existence of further lingual receptors in humans is currently being discussed. In rodents, for example, receptors for the detection of free fatty acids have been found that are believed to play a role in signalling energy dense, fat containing foods. Whether taste receptors for detecting other than the five basic tastes of sweetness, saltiness, sourness, bitterness and umami exist remains to be determined.