The new role of glutamate
―Can umami be sensed by both the tongue and the stomach?―

Our sense of taste plays the role of signalling which foods are good for us and which are harmful. A sweet taste signals a source of energy through sugars and carbohydrates. A salty taste signals the presence minerals that are essential to keep the mineral balance of body fluid. In the natural world, sour taste is a signal of food that has degraded or tastes of unripened fruit, A bitter taste, meanwhile, signals that something is harmful to the body, such as a toxin. On the other hand, umami is the taste of amino acids or nucleotides, and plays the role of signalling the presence of proteins, which are essential to human beings.

On the surface of the tongue, there can be found nodules and amongst these are nodules that serve to recognise different tastes, called taste buds. On these taste buds there are taste receptors, and it through these that the various tastes of sweet, sour, salty, bitter and umami are recognised by the body. For example, when the umami taste receptors on the taste buds come into contact with glutamate this information is relayed to the brain via the vagus nerve and the umami taste is recognised by the brain.

What is more, recent research has discovered that there are glutamate receptors not only on the tongue but also in the stomach. It has been ascertained that the pneumogastric vagus nerve only reacts to glutamate, and amongst amino acids it reacts only to glutamate. This suggests that when a piece of food enters the stomach, and glutamate receptors detect the presence of glutamate this information is relayed to the brain by the vagus nerve and an order is sent from the brain to the stomach to prepare for digestion of food.

The mechanism by which umami is recognized. Click to view diagram

The latest studies suggest that glutamate has an important function to operate normal digestion of dietary protein. In addition to this study, a research group is investigating the effect of glutamate added to a non-protein diet. Preliminary data suggests that glutamate has the possibility of regulating digestion of food -based protein and carbohydrate (due to nutrient homeostasis within normal limits).