Sweet TRPM5

Today is National Chocolate Fondue Day and here is an interesting fact: even though hot and cold chocolate have the same amount of sugar, you may find that hot chocolate tastes sweeter.

So why is that? Let me remind you how our taste perception works. When we eat or drink, tasty compounds interact with specialized receptors in the taste buds of our tongue and palate, causing an electrical excitation of taste receptor cells. This excitation is then sent to our brain for the final interpretation of each taste.

Obviously, the electrical excitation of taste receptor cells is controlled by ion channels, and for sweet taste, it’s the TRPM5 ion channel that is believed to play a major role. TRPM5 is highly expressed in taste buds of the tongue and is activated downstream of specialized G-protein-coupled taste receptors that bind sweet compounds.

In 2005, Bernd Nilius Group showed that TRPM5 is a temperature-sensitive ion channel that is activated by heat. They found that increasing the temperature between 15 and 35°C markedly enhances the gustatory nerve response to sweet compounds in normal mice, but not in mice without TRPM5.

Since TRPM5 is activated by both sweetness and heat, hot chocolate creates a stronger electrical excitation of taste receptor cells than cold chocolate, making it appear sweeter to our brain.

That’s why chocolate connoisseurs suggest tasting chocolate at around 18-20°C, where it will taste less sweet, and you’ll get more of the chocolate flavor.

But today is Chocolate Fondue Day! So go ahead, melt your chocolate, grab some marshmallows, bananas, strawberries or whatever you like, and enjoy the hot sweetness brought to you by TRPM5.