Besides the the six tastes (it’s six because of fat, see a previous post), we also have other sensations in our mouth. We can sense when something is spicy hot, as when food has cayenne or wasabi, and when it has a chemical coolant, such as the menthol in chewing gum. These sensations are different from tastes because they rely on little (molecular little) tubes on the nerve cells. They are not in our taste buds but in our mouth and throat. These little tubes allow certain molecules to enter the cells and change some of the chemical reactions that are going on inside. This is how we perceive spicy hot, temperature, and a few other things no one is quite sure.

These little tubes are known as TRP ion channels. They let ions and some small molecules in and out of cells. Because they are made out of proteins that look like each other, biologists have checked that the human genome codes for at least 28 different TRP ion channels. The fun part for scientists is that most of them have unknown functions. One of them, trpa1, seems to detect low temperatures (under 15°C) but also the hotness related to mustard. Maybe there is some room for culinary experimentation with mustard or wasabi ice creams. (Exotic ice creams are now all the rage. Heston Blumenthal churned mustard ice cream early on, but I’ve never tried it.) The little ion tubes can be desensitized by certain chemicals, which opens up other culinary possibilities.

Sour and salty seem to use mainly TRP channels, but the other tastes use specialized cell membrane molecules called GPCR. The GPCR communicate to the inside of the cell the presence of some molecule on the outside. Say you have just eaten a nice piece of chocolate cake. The sucrose from the sugar will find its way to a taste bud. A taste bud has many taste receptor cells (often abbreviated TRC) and each cell will have a different collection of GPCR. Sucrose will stick only to one type of GPCR called T1R2+T1R3. The GPCR with the captured sucrose moves along the cell membrane and with the help of other molecules produces camp, which is then used to activate enzymes and start other reactions in the taste receptor cells that will signal the brain that a sucrose was inside your mouth.

We have one GPCR for sweet, one for umami, and it looks like one for fat. But we have over 30 for bitter. We cannot tell one bitter taste from another: the GPCR for bitter tend to be on the same taste receptor cell, so the brain cannot tell them apart.