Last night I was cutting up some of my homegrown Serrano chilies.  I made a pretty good salsa with them (thanks to iNow for the recipe).  However, I wasn’t prepared for the extreme heat of the peppers.  I bit into one and my mouth almost literally caught on fire.  I ignored the pain though and finished the salsa.  About an hour later my hand started to burn and no amount of soap and water would significantly reduce the pain.  As of right now, I’m still feeling it.

Being the naturally curious person, I wanted to find out more about why my hand felt like it was being knawed on by a million angry Gremlins.

Enter Capsaicins, the active ingrediant of the spicy heat of chilis:

Its a hydrophobic compound (which would explain why the water didn’t help) colorless and odorless but certainly not tasteless.  It’s also an irritant for all mammals. Capsaicin is the most abundant of the capsaicinoid molecules found in chili peppers.  The structure was first defined in 1919 by E. K. Nelson.

The capsaicins are found most abundantly in the placental tissue of the fruit.  That is mainly the inner membranes and the white tissue holding the seeds, known as the pith, but not actually in the seeds themselves and in small amounts in the outer skin.  Birds, which lack capsaicin receptors eat chilies and distribute their seeds after they pass safely through their digestive tracts.

In diluted form, the capsaicins are great for food, but can cause burning sensations when exposed in high concentrations to mucus membranes and skin, as I have discovered.  The Scoville scale is a relative measure of how hot a pepper is, on the basis of perception.  To demonstrate the scale, a bell pepper would get a zero rating, jalapenos are 2500-8000 (I assume non-pickled).  My serranos would be rated around 10000 to 23000 and habeneros are 100000 to 350000.  The Dorset Naga (yes grown in Dorset, England) tops the scales at 876,000 to 970,000.  Nothing beats pure capsaicin, however, which weighs in at a hefty 15000000 on the Scoville scale.

So why do these capsaicins hurt so much?  Its because they interact with sensory neurons.  Capsaicins bind to vanilloid receptor subtype 1, an ion channel receptor which can also, incidently be stimulated by heat and abrasions.  When opened, the channels allow calcium cations to pass through, depolarizing the cell membrane potential.  From here, the electrical signal propogates down the neuron and is percieved ultimately in the brain.

So the reason why chilies make you feel like your toungue or hands are on fire, is because that’s exactly how your brain intepretes the neuronal signals.  Of course, you know that there’s no actual heat present but, in this case perception is reality.  Its nice to know that, while it may feel like you tounge is going to fall off, the capsaicins probably won’t cause real physical damage.  However, it is an irritant, so injesting a large amount can be reasonto call the poison control center.

On the plus side, capsaicinoids have been useful in medicine, from treating topical pain in neuropathy to treating cancers and diabetes.  Capsaicins can be a part of a healthy diet, as shown in epidemiological studies.  Regions, such as Thailand, which use a healthy amount of chilies in their cooking have lower incidence of GI cancers.  Capsaicins have been shown to promote apoptosis in lung cancer cells. New research also suggests that capsaicins could help reduce drug dependency.

So chilies taste good and are good for you, as long as you don’t over-ingest.

I can’t wait to go home and try my hot salsa.

This entry was posted on Friday, August 8th, 2008 at 11:47 am and is filed under biochemistry, medicine, neurobiology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.