Hot drinks and sweetness

Temperature has a strong influence on how we taste. The sweetness of diluted sugar solutions increases strongly with temperature. Merely cooling or heating the tongue is sufficient to cause sensations of taste in approximately 50% of subjects.
Several members of the TRP super family function as thermosensors and this has been studied by Talavera et al Nature 2007, vol 438, 1022- 1025 to attempt explain what is happening in the tongue. The TRP super family are Transient Receptor Potential channels .
TRPM5, is an intra-cellular calcium -activated, voltage-dependent channel of the TRP superfamily, and is highly expressed in taste buds of the tongue, where it has a key role in the perception of sweetness , umami and bitter tastes. Activation of TRPM5 occurs downstream of the activation of G-protein-coupled taste receptors and generates a depolarizing potential in the taste receptor cells:. Factors that influence TRPM5 activity are therefore expected to influence taste.
Talavera et al have shown that TRPM5 is a highly temperature-sensitive, heat-activated channel. Inward TRPM5 currents increase steeply at temperatures between 15 and 35 degrees centigrade
Increasing temperature between 13 and 35 degrees centigrade markedly enhances the gustatory nerve response to sweet compounds in mice. The strong temperature sensitivity of TRPM5 may underlie known effects of temperature on perceived taste in humans, including enhanced sweetness perception at high temperatures and ‘thermal taste’, the phenomenon whereby heating or cooling of the tongue evoke sensations of taste without any taste being involved.
Which is why a hot sweet cup of tea can taste so deliciously in certain circumstances. It’s the TRPM5 at work.

Martin Eastwood
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