This Week's Experiment - #261 Pepper Hot
I got the idea for this week's show while eating dinner. I was eating a spicy meal at a Chinese restaurant, and it suddenly occurred to me that the
"hot" taste of the Chinese mustard was very different from the "hot" taste of
the Kung Pow Chicken. To get a taste of an interesting area of science, you
will need several of the following:
hot cinnamon candy
hot sauce
horseradish
ginger
peppermint candy
wintergreen candy
spearmint candy
What do all those things have in common? They all stimulate your trigeminal
nerve. This nerve branches to your mouth, nose and eyes and it is very
sensitive to certain chemicals. Depending on the chemical, the sensation can
register as heat, cold, or pain. Depending on how concentrated the chemicals
are, you can get the pleasant cooling of an afterdinner mint, or the blazing
pain of a mouth full of very hot peppers.
The hot sensation of my Kung Pow Chicken and the hot and sour soup came from
peppers. You can get a similar sensation by tasting some hot sauce. Peppers
contain capsaicinoids, a group of chemicals that are concentrated in the
seeds and the white membranes on the inside of the pepper. Capsaicinoids
stimulate the thermal and pain receptors in the trigeminal nerve, producing a
sensation that can range from pleasantly warm to very hot. The capsaicinoids
are dissolved in oil, which is why water does not seem to help much in
getting rid of the heat from a really hot pepper. Water and oil don't mix,
so the water does not remove the chemical. Milk works better, as the
capsaicinoids will dissolve in the milk fat, and it can then carry the
irritant away.
The hot mustard that came with my egg roll produced a very different
sensation. Instead of a sensation of heat on my tongue, the mustard sent a
strong, almost painful sensation into my nose and sinuses. Mustard and
horseradish contain isothiocyanates. These chemicals vaporize and are easily
carried into the nose. There they stimulate the same group of nerves, but
with a very different sensation. It is not really heat, but more of a pain
or "bite." Since they vaporize so easily, the sensation does not last nearly
as long as the heat from peppers.
Mints act on the same nerves in a very different way. Instead of registering
as heat, mints contain menthol, which stimulates the trigeminal nerve with
the sensation of cold. Menthol dissolves in oil like the capsaicinoids from
a pepper, but it also vaporizes like the isothiocyanates from horseradish.
This means that you feel the mint in your mouth and your nose. This can be
mild or almost as painful as a hot pepper, depending on how concentrated it
is.
Other foods contain chemicals that stimulate the trigeminal nerve, such as
ginger (gingerols), onions (Diallyl sulfide) and black pepper (pipperine).
Since it is not really a taste or a smell, many sources list it as a separate
sense, the trigeminal sense. The next time you want to investigate your
sixth sense, head for your nearest Chinese restaurant. Be sure to have some
steamed dumplings for me. Yum!
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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