Some new research sheds light on why chili plants are spicy:
It has been thought that the chemicals known as capsaicinoids, which surround the seeds and give peppers their characteristic heat, are the chili’s way of deterring microbes. But if so, then microbial infestation should bring selective pressure on chilis — the more bugs, the hotter the peppers should be.
That has never been shown in the wild. Now, however, in a study of wild chili plants, Joshua J. Tewksbury of the University of Washington and colleagues show that the variation in heat reflects the risk that the plants will be attacked by a seed-destroying fungus.
My own little vegetable garden has been hard hit by fungus this year, but the hot peppers are in full bloom. Now I know why – capsaicin is the original fungicide.
Of course, that still doesn’t explain why capsaicin tastes “hot,” and why spicy food “burns” our tongue. For that, we need to investigate the physiology of taste. It turns out that capsaicin – this plant protectant – binds to a special class of vanilloid receptor inside our mouth called VR1 receptors. After binding capsaicin, the neuron is depolarized, and it signals the presence of spicy stimuli.
But here’s the strange part: VR1 receptors weren’t designed to detect capsaicin. They bind spicy food by accident. The real purpose of VR1 receptors is the detection of heat. They are supposed to prevent us from consuming food that is too hot, in the thermal sense. (That’s why our VR1 receptors are clustered in our tongue, mouth and skin.) So when they are activated by capsaicin the sensation we experience is that of excessive heat. We start to sweat and get the urge to drink lots of water. But that pain is just an illusory side-effect of our cell receptors. There is nothing “hot” about spicy food.