Science behind Spiciness

Whether for pain or pleasure, at some point in your life you will probably have eaten a hot chilli. Having lost a bet at lunch, It makes a great forefit for any competition between school friends.

While my mouth was on fire after eating a "birds eye" chilli I wondered exactly what it is about chillis which causes such a reaction, so I decided to do some research on it.

The tongue has a multitude of different receptors for different flavours and sensations, including one called "TRP-VR1" (Vanilloid Receptor 1) which detects  actual heat- if you were to eat something which has a high temperature these receptors are activated, letting a flood of ions through a protein channel, travelling through the nervous system and reaching the brain, which interprets the signal as "ouch", and so pain is felt.

Capsaicin

The active ingredient in any chilli is a molecule called capsaicin- C₁₈H₂₇NO₃. This molecule binds to the receptor, forming a waxy layer over it and signals it to open the protein channels making your brain feel heat pain on your tongue or wherever the capsaicin contacted. (The eyes, inside of the nose and other mucous membranes also contain these receptors, which is why getting any in your eyes or up your nose hurts all the same) the waxy nature of capsaicin from its hydrocarbon tail means it is non soluble in water, explaining why water does nothing to help wash away or cool down the mouth.

Bird's eye chilli

There is a scale to measure the "heat" of a chilli called the Scoville scale, devised by an American pharmacist, Wilbur Scoville in 1912 (whose birthday happens to be toady). In the test to determine how hot a chilli is, a panel of at 5 "expert taste testers" eat an exact weight of dried chilli dissolved in alcohol to extract the capsaicin and then are given a sugar water drink until at least 3 of the 5 agree there is no heat left. Of course the test is no perfect and often has varying ranges for the same chilli due to the human perception of when there is any heat left. The scale graduates in 100s of Scoville heat units (SHU). At the lowest end is a bell pepper, at 0 SHU and paprika at 100 SHU. Nice heat you might find in a mild tesco curry would be around 500 to 1000 SHU. Above 20,000 SHU is usually not considered to be a nice heat on its own, like Tabasco sauce. Hot supermarket curries may have 100,000 SHU. The birds eye chillis we buy and use in school are about 200,000 to 300,000 SHU. When I eat them my eyes and nose stream and I can't feel my mouth for a good 15 minutes, past this point there is only discomfort. My uncle
used to keep some naga chillis which are 750,000 SHU, and I have seen videos of people who do the most ridiculous chilli challenges online  using the famed "ghost pepper" which comes in at 1,000,000 SHU. The hottest pepper officially ever grown was the Carolina reaper, achieving a painful 2,200,000 SHU- about 10 times as hot as the ones I have had. 

The Carolina Reaper

But all of these chillis have extra flesh and other chemicals in them which hold off the heat of pure capsaicin. The chemical is used in higher concentrations in pepper spray, which comes in at 5,000,000 SHU. Pure crystal capsaicin  is pretty awful stuff, peaking at between 15,000,000 to 16,000,000 SHU. This kind of heat can just blow your head off-and has been made illegal in the United Kingdom as of 2013. 

Chillis make these chemicals as a defence mechanism, as most animals are affected by it, and wouldn't ever dare eat it again after the painful ordeal. Farmers who try to breed the hottest chillis tend to make harsh environments, apparently sometimes even cutting off branches of the plant in an effort to make them "feel as if they are being eaten, so they make their chillis hotter" I have heard stories about some chilli farmers verbally abusing their plants in an effort to make them hotter, although I don't really see the science behind it. 

Birds are one of the few animals which are not affected by hot peppers because they don't possess any TRPVR1 receptors. 

In nature there are compounds made by specific plants which actually do a better job than capsaicin can do on your receptors. 

Euphorbia poissonii, a highly toxic plant grown in Nigeria contains a chemical called Tinyatoxin, which clocks in at 5,300,000,000 SHU- over 300 times hotter than pure capsaicin, and 1000 times hotter than law enforcement grade pepper spray. Nigerian farmers reportedly use the plant's fluids as a pesticide.

Euphorbia Poisonii

Above: Tinyatoxin-(5,300,000,000 SHU)

Below: Resiniferatoxin-(16,000,000,000 SHU)





Even Tinyatoxin's heat pales in comparison to the King of chemical heat: Resiniferatoxin. Although the only difference between it and Tinyatoxin is the ether group on the carbon ring on the right side of the diagram this chemical is the ultra active analog of capsaicin, making the police's pepper spray seem harmless. It weighs in at 16,000,000,000 SHU of course this and Tinyatoxin's Scoville heat ratings have been estimated based on chemical analysis, because as little as 10 grams of it is a fatal dose, overloading the nerves which signal pain, and giving respiratory failure. Very very small mixtures of these chemical, although it seems illogical, have been used as effective pain medication due to numbing effects and are even being used in treatment of Peripheral neuropathy, to help nerve pathways refire.

 Left: Euphorbia Resinifara

Resiniferatoxin is found in Euphorbia Resinifera- a type of little cactus in north Morocco. As if spikes weren't enough to keep animals away from a cactus! I think I'll stick to the bird's eye chillis...