Just this January a review paper came out detailing how capsaicin, the burning compound in chili peppers, interacts with TRPV1, the hot receptor, on trigeminal nerve cell endings in the mouth.* It turns out that we know a lot about how capsaicin works with TRPV1 to cause sensations of heat and pain.
Capsaicin has to make its way across the nerve cell’s membrane to activate TRPV1 from the inside. That’s why it takes a beat before you feel the pain when you eat some chili.
Once inside the nerve ending, it causes the TRPV1 channel to open up and allow ions to enter the cell. This ion movement, in turn, triggers all the sensations of heat and pain you get from capsaicin.
It’s interesting to note that heat—by which I mean hot temperatures—increases the effects of capsaicin: a food with capsaicin served at hotter temperatures will burn more than a food served at colder temperatures. Similarly, capsaicin makes a warm food seem hotter than it actually is.
Which specific tastes, such as sweet and bitter, do to capsaicin’s burn has been the subject of much controversy, because of the difficulties in carrying out proper experiments. How do you deliver the capsaicin to the mouth—it’s poorly soluble in water, so do you use papers or resins or even alcohol (which activates TRPV1 all by itself!)? What should the timing be—repeated deliveries of capsaicin may either increase or decrease sensitivity depending on the time in between applications and their frequency, so how often to deliver the solutions and for how long? How do you manage alternating capsaicin with the sweet etc. solutions—the order may be important—or do you deliver the solutions (capsaicin and other tastant) at the same time?
All manner of permutations of these parameters have been tried, and the only consensus (more or less) is that sweet tends to diminish the burn, and sour, if it does anything, increases it (or maybe decreases it…).
This consensus makes sense to me personally—as many of you know, I love Vietnamese food but am very sensitive to capsaicin. One item in Vietnamese food is the chili sauce, which comes in sweet and sour varieties at my local places. The number of red flecks of chili in each is pretty much the same. I can tolerate the sweet variety, but oh how the sour variety burns!
The Vietnamese sauce I'm talking about, from one of my favorite restaurants, Saigon Kitchen in Ithaca New York. (Photo from TripAdvisor)
One other aspect that presents a problem for these experiments: genetics, namely the genetics of our TRPV1 receptors. It is becoming clear that there are many genetic variants of this receptor, which confer differing degrees of sensitivity to capsaicin and also to other compounds such as alcohol, sweet compounds, and sodium chloride. To the best of my knowledge, no study of pairing chili peppers with other tastants has taken these genetic differences into account as yet.
My conclusion: it’s up to you to decide how much capsaicin you can tolerate and with what other foods. But if you are like me, sweet helps...and fat turns off TRPV1, and with it the burn. How? We don't know but it works.
*Gregory Smutzer and Roni K. Devassy. Integrating TRPV1 Receptor Function with Capsaicin Psychophysics. Adv Pharmacol Sci. 2016; 2016: 1512457. Published online 2016 Jan 14. doi: 10.1155/2016/1512457. You can find the full free article here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4738735/
** For more about the trigeminal nerve, see the Monday, February 29, 2016 post.
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