Help, fire in my mouth!
Ahh, the hot pepper! Few foods can be claimed to be loved (or hated) by so many. Whatever your stance on feeling the burn may be, these peppers have been an indispensable spice through history, and still are around the globe. Mexican and Asian food, for example, still make heavy use of this plant. Though the spice may bring the heat, it is undeniable that this adds a unique flavour to foods. We all have different tolerance for spice; while some of us may be running for a drink at the mere sight of a chili, others gobble them down with relish, some people even competing in chili eating competitions. This burning sensation is caused by capsaicin and several related substances that are collectively known as capsaicinoids. This name was taken from the latin name for the pepper genus and shared with these substances, since they can be found in various members of this genus.
Capsicum is a genus native to the Americas and belongs to the family Solanaceae, which also includes tomatoes, potatoes, eggplants, and tobacco. Domesticated species such as Capsicum annuum, Capsicum baccatum, Capsicum chinense, Capsicum frutescens, and Capsicum pubescens are a source of chilli (tabasco, halapeño, habanero), and are used in spicing many other foods.
Capsaicin was first extracted by the German pharmacist Bucholz in 1816 and was then called capsicin. Thirty years later, it was isolated in a purer form by Thresh and named capsaicin. It structure was partly explained in 1919, with the first confirmed complete synthesis arising in 1930. In addition to capsaicin (69%), various related compounds are found in peppers including dihydrocapsaicin (22%), nordihydrocapsaicin (7%), homodihydrocapsaicin (1%), and homocapsaic (1%).
The effects of capsaicin are as a result of their irritation of our bodily heat sensors. By binding to specific sensory cells that detect heat and pain, it triggers nerve impulses that travel to the brain. These sensors are proteins that are known as subtype 1 (VR1) vanilloid receptors. As they are designed to sense heat and pain, their triggering tells our brain that we are hot, even though the temperature may be perfectly normal.
Capsaicin is a defensive compound that some plants have evolved to protect themselves from different animals. That being said, evolution is a funny thing; who could have known that humans would be so masochistic and enjoying this burning sensation? Now, in an ironic twist, this spiciness that was developed to keep creatures from eating this plant is exactly why we eat them!
In terms of the intensity of the burning sensation in peppers, it is measured by a scale introduced by Amercian pharmacist Scoville in 1912, which is named after him. According to the Scoville scale, a hot pepper has 100-500 units, halapeño chilli has 2500-8000, tabasco chilli has 30,000-50,000, habanero chilli has 100,000-350,000, and pure capsaicin as many as 16,000,000 units (yikes). That's surely enough to burn the love of spice out of any mouth! The Scoville test is an organoleptic test, meaning that it is measured using the senses of volunteer testers. In order to do this, the required amount of a sample is extracted in a prescribed quantity of alcohol before a series of different diluted solutions is prepared with water. A group of 5 trained testers find the point of dilution in which most of them (at least 3/5) can no longer detect a burning sensation. The dilution rate is then Scoville's estimate of the intensity of the burning sensation. Pure capsaicin can still be detected even when diluted by a factor of 15 million! This means it's so hot that you could dissolve a knife's tip worth of it in 1000 litres of water and still taste it! Thankfully, only small amounts (rarely above 0.1%) are found in most hot pepper species. This compound is only produced in the fruiting body of the plant, and is strongest and most concentrated in the flesh near the seeds.
Capsaicin does not actually cause chemical burns, just the sensation of burning. Large amounts of pure capsaicin can be life-threatening, but consuming hot peppers is not a threat as it does not actually damage the gastrointestinal mucosa. For those of you who have experienced this burning before, you probably wanted to reach for a glass of water to extinguish the flames. Let us tell you, that's a mistake! Capsaicin is actually not very soluble in water, so this does not help much. It is, however, more soluble in fat, so rinsing the mouth with something oily or fatty will help. That being said, even with this method, it will take some work since it can be felt still at such weak dilutions.
In opposition to capsaicin and its activation of heat receptors, menthol from peppermint activates cold receptors. Though this may make you think that you can use menthol to nullify capsaicin with menthol, this is unfortunately untrue as the two substances act on different receptors. If the receptors are nullified by actual heat or cold, however, then the effects will be nullified.
As a result of their strong taste, hot peppers are good for stimulating appetite and the secretion of digestive juices in individuals with poor digestion. Similar effects can be achieved by using very bitter or aromatic plants. Peppermint preparations are used externally for relieving pain (for example in shingles). It is also used to stimulate blood flow, especially in cellulite and cold feet.
The hot peppers and their relatives came to Europe only after the invasion of the Americas. In antiquity and the Middle Ages, however, a different plant was used for this spicing purpose. Sharing the same name in English, pepper (from the Piper genus) comes in a range of varieties, but rather than containing capsaicin uses piperine for its taste. Pepper was the spice of the rich, and its worth was greater than that of gold! It is no surprise that Columbus's expedition to India was funded primarily in order to find a new route by which to get pepper to Europe. That being said, he found neither, instead stumbling upon the Americas and the chili pepper.
After a second voyage in 1493, Columbus brought this plant to Europe, where it was soon used as pepper for the poor.
Other plants have a spicy taste too...
Plants of the Brassicaceae family such as horseradish, wasabi, cabbage, and mustard contain senevolous glycosides, while some of the Amaryllidaceae such as onions and garlic contain derivatives of iline. Both of these substances contain sulphur, but they are actually quite different in chemical structure. As long as they are in the plant, these compounds are not volatile. When the plants are cut, broken, or chewed, however, a chemical reaction occurs that releases volatiles that burn the oral and nasal cavities. Piperine is not volatile and capsaicin is only partially volatile, which is why these spices are only felt when we eat them and the sensation stays mostly limited to our mouths. Another burning substance is gingerol, found in ginger.