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Part 4: Chemistry of chili peppers
 As
mentioned in Part-3 of this series, chili hotness is measured in
Scoville Heat Units (SHU) which was originally a subjective
measure characterized by organoleptic (mouthfeel) evaluation by
a panel of human testers. An extract of the chili pepper was
sequentially diluted by orders of magnitude and tasted by the
panel until they felt it was not at all hot. The dilution factor
(say 10, 100, 1000 etc) was then determined to be the SHU. Now
it is determined precisely by HPLC (High Pressure Liquid
Chromatography) by equating 15 Scoville units to 1 ppm (part per
million) capsaicin (which affords the pungency to the chilies).
The Central American species Capsicum chinense is characterized
by an SHU of ~300000. A proprietary cultivar, red savina
habanero, rates at around 560000 SHU while the jalapeno,
considered hot by American standards, come in around 5000 SHU.
Let us understand what contributes to the heat.
Capsaicin (8-methyl-N-vanillyl-6-nonenamide)
is the active component of chilli peppers. It is a volatile
phenolic chemical similar in structure to vanillin, present in
the placenta that bears the seeds in the chili pepper. It is an
irritant for mammals, including humans, and produces a sensation
of burning in any tissue with which it comes into contact.
Capsaicin and its analogs are called capsaicinoids and are
produced by chilli peppers, probably as deterrents against
herbivores perhaps through an evolutionary process. Capsaicin is
a flavorless, odorless chemical concentrated in the veins of
chillies. Capsaicin and dihydrocapsaicin constitute 80-90 per
cent of the total capsaicinoids in a chili pepper.
 When
chili pepper is consumed the capsaicinoids bind to a receptor in
the mouth lining. This is the same receptor that registers pain
from heat (temperature) and hence a burning feeling is
recognized. It then stimulates the brain to release a
neurotransmitter called substance P which triggers a cascade of
events. The mouth starts salivating, the tongue burns, the nose
runs, the eyes might start to water, and a sweat breaks on the
face. The heart beats faster and the endogenous painkillers
called endorphins are secreted from the brain to” douse the
flame” so to speak and pretty soon the pain mitigates. Repeated
exposure to capsaicinoids depletes the receptors of the taste
buds in the mouth thereby enabling one to eat hotter chillies
and build a tolerance.
What can be done to combat the heat of the
chilies? Capsaicin is a hydrophobic molecule and hence not very
soluble in water. One cannot wash away the capsaicin by drinking
water, beer, or wine since doing so will scatter the capsaicin
over a wider area in the mouth causing greater burn. The best
extinguishers are: milk, cream, cheese, bread, and potatoes.
 The
amount of capsaicin in peppers varies widely and dependent on
the genetics of the plant. Capsicum chinense has 2 per cent
capsaicin (weight per dry weight of the chilli) and the red
savina habanero has 3.7 per cent capsaicin. The only pepper
without capsaicin is the bell pepper which is sweet to the
taste. In addition to capsaicinoids, chili peppers also contain
essential oils which give fruity flavors. Chillies are also high
in vitamin C (twice the amount found in citrus fruits). Ripe and
dried chillies are high in vitamin A and beta carotene.
Capsicum oleoresin is a chili extract used to
make ultra hot sauce and also the chemical riot control agent,
pepper spray. Chilies have had other uses in the past besides
spicing up a meal; the Incas of Panama used to tie strings of
chilies to their boats to ward off sharks.
Part 1 |
Part 2 |
Part 3
Sethuraman
Subramanian
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