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Physiologists discover how temperature influences our taste

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16.12.2005

The sweet taste of temperature

Why does a beer taste better if it comes from the fridge and does a warm beer taste bitter? Why is red Bordeaux wine best drunk at room temperature? And what causes that unique taste sensation of ice cream? Researchers from the Physiology section of the Katholieke Universiteit Leuven (K.U.Leuven, Belgium) have discovered, together with their Japanese and American colleagues, how the temperature sensitivity of our sense of taste works. Today, they publish their breakthrough in the top professional journal Nature.

How does taste recognition work?

People can distinguish five basic tastes: sour, sweet, salty, bitter, and umami (the Japanese term for the bouillon-like taste found in, for example, meat and mature cheeses). The perception of taste occurs in the taste buds in our tongue. These buds contain taste receptors, specialised proteins able to recognise sweet, bitter, and umami taste molecules in food and drinks. When taste molecules touch the taste receptors, microscopic channels – termed TRPM5 – open in the cell membrane of the taste buds. This causes an electric signal to arise in the taste buds that travels to the brain via nerve fibers, where it is translated into a specific taste sensation.

K.U.Leuven’s physiologists decipher the temperature sensitivity of our sense of taste

Physiologists from the university of Leuven have discovered that this Trpm5-channel in our taste buds is highly sensitive to changes in temperature. At 15ºC the channel scarcely opens, whereas at 37ºC its sensitivity is more than 100 times higher. The warmer the food or fluid in your mouth, that much stronger will TRPM5 react, and thus that much stronger is the electrical signal sent to the brain. For example, the sweet taste of ice cream will only be perceived when it melts and heats up in the mouth. If you serve the same ice cream warm, then the reaction of TRPM5 in your taste buds is much more intense and the taste of the melted ice cream is much sweeter.

Based on these findings, K.U.Leuven’s researchers now conclude in Nature that TRPM5 lies at the basis of our taste’s sensitivity to temperature. This was also confirmed in experiments on mice: taste responses increased dramatically when the temperature of sweet drinks was increased from 15°C to 37°C. This temperature sensitivity of sweet taste was entirely lacking in genetically altered mice that no longer produced the Trpm5 channel.

This research opens the way to the development of chemical substances influencing the functioning of the Trpm5-channels so as to suppress unpleasant tastes, for example, or to explore completely unprecedented and new taste experiences.

Finally, these results provide an explanation for a well known psychophysical experiment, whereby test persons experience taste sensations just by heating specific parts of the tongue. Leuven’s researchers attribute this phenomenon to a direct activation of TRPM5 in the taste buds. Indeed, at higher temperatures the sensitivity of TRPM5 increases to such a degree that it becomes activated in the absence of taste molecules, leading to a “thermal taste” signal to the brains.

Luc West | Source: alphagalileo
Further information: www.nature.com/nature/journal/v438/n7070/abs/nature04248.html

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