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Questions about how capsaicin works...

Here are some things I'm wondering about:

Why do some peppers burn the throat, while others the tongue, etc. For example, I have one sauce that makes me feel like I burned the tip and sides of my tongue on hot coffee. A distinct and predictable pattern. But other sauces do not.

Why do I sometimes reach the point of numbness, when other times, the burn keeps building and building, never easing up? Is there a trick to triggering the "numb" response?

If the burn is cause by the alkali nature of capsaicin, then why doesn't the vinegar and citrus juice used in sauces decrease the heat? Will the capsaicin not bind with the acids?
 
The burn is not caused by the "alkali nature" of capsaicin. Perhaps your are thinking of alkaloid, but that means something different. Capsaicin binds to TRPV1 receptors (vanilloid receptor subtype 1) which are typically responsible for heat sensation.

I'm not really sure what causes the different burns, but its possible the different capsaicinoid compounds are responsible for this effect.
 
Capsaicin is not alkaline which means it is not a base. It will not suck up the H+ ions in the water like a normal base such as baking soda would. Capsaicin is a lipid of sorts, and has a nice little fatty acid tail coming off of it, which means it actually repels water for the most part (hydrophobic) and would much rather dissolve in another lipid or a non-polar solvent (lipophilic). This generally means it won't have any major effect on pH.

That being said, the pain in different parts of your mouth tends to be caused by different types of capsaicinoids. There is dihydrocapsaicin, nordihydrocapsaicin, homocapsaicin, etc. The main differences between these compounds is the end of the fatty acid tail. Some of the tails are completely saturated (no double bonds) and some aren't. These different molecular shapes change how the molecule will trigger the pain response in different parts of your mouth. We can probably infer from this that the ion channels that will cause the pain from capsaicinoids differ slightly between the tongue/throat/lips/etc. I couldn't find much information on WHY they cause different reactions, but the body works in very complex ways and can treat two very similar compounds quite differently.

I hope this helps.
 
This was brought up not that long ago and Matt is correct. The different types of capsaicinoids effect different parts of the mouth.
 
Where are you guys getting this information about different parts of the mouth? I've seen it mentioned plenty of times.
 
There's a number of studies that have been done that I've had a hard time locating online. Here's an article that outlines some of it.
http://www.fiery-foo...re-of-capsaicin

Capsaicin and Dihydrocapsaicin are said to cause an intense burning all over the mouth.

Nordihydrocapsaicin is said to be the least irritating, causing a steady warming sensation that hits mostly the front of the mouth.

Homodihydrocapsaicin is said to create a numbing sensation and a very sharp burn, particularly at the back of the throat that continues to build and is hard to wash out.

I'll have to keep looking for sources, my apologies. When I'm not writing a research paper I get lazy and just type from the old noggin...
 
I've got some undergrad students in a class I'm teaching who are doing a senior project on capsaicinoid extraction and they asked me the very same question. Didn't have an answer for them, so did a journal search and found only one article ("sensory properties of naturally occurring capsaicinoids", Krajewska and Powers, Journal of Food Science, 1988). It basically says what mrz1988 posted (probably the source for the article you posted).

Yeah, as to why, I have no idea. Asked some I my biochem colleagues and they couldn't give an answer, and they didn't care to find out (not chileheads - biochemists are weak and cant handle the heat). If anybody ever figures it out, definitely post something!
 
Weird things I have experienced lately ...
My Datil sauce is by far creates the most pain in my mouth, even thoughdatils are only about as hot as a habaneros.

Melinda's jolokia sauce causes a lot of heat pain too of course, but it also causes a very warn feeling in my chest that lasts most of the day. That is the only thing so far to give me a feeling in my chest (not talking about heart burn or reflux).

Also, I was experimenting in the kitchen today, doing a lot of tasting. The off and on burn over several minutes made my tongue go almost numb. For dinner tonight ( four hours later), I put a lot of home pickled jalapenos in my bowl of chili, and didn't feel the slightest thing as far as pain, although I was sweating profusely and having my eyes water/nose run.

I don't know how it all works!
 
As for the why part, likely because of the way taste receptors (taste buds) are distributed. There's some controversy on them being distributed in the classic sweet, salty, sour, bitter pattern most people learn about in grade school, but different nerves do receive taste information from different parts of the tongue, and that is pretty much divided as anterior 2/3, posterior 1/3, and some overlap of the posterior part with the "root" of the tongue and epiglottis, which would be more of the back of the mouth and throat type sensations. You can also taste some from the palate too. The different types of capsaicin might preferentially signal receptors carried by the different nerves. This actually sounds like something that would be fun to research, but I'm pretty sure funding priority should go to more serious problems than tasting capsaicin.
 
Actually taste receptors are not responsible for the heat. Does it not burn coming out? Or how about when you get it on your skin or in your eyes?
 
Sounds like that portion is controlled by your body's absorption of the fatty acids, after all we are made up of lipids. That could still cause nerve pain. When you rub your eyes it's generally the same type of pain, when I eat spicy food the after-pain is always the same every time, I think the mouth would have to do more with having lots of available bonding sites connected to different nerve groups, affected by the shape of the capsaicin molecule.
 
I had another, less scientific thought on the subject lately. Why would a particular sauce only burn the back of my tongue? Maybe because I had been sampling sauces earlier that day, which had made the bulk of my tongue go numb? If the pain receptors in the back were all that hadn't been "spent", then I would only feel the burn in that area.
 
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