Capsaicin
Capsaicin is a toxin that is the main active component of chili peppers and gives them their "spicy" or "hot" taste. It is a potent irritant for mammals, including humans, for which it produces a sensation of burning in any tissue with which it comes into contact. Capsaicin and several related amides are produced as secondary metabolites by chili peppers, likely as deterrents against eating by mammals and against the growth of fungi. Pure capsaicin is a hydrophobic, colorless, highly pungent crystalline solid.
Natural function
Capsaicin is present in large quantities in the placental tissue, the internal membranes and, to a lesser extent, the other fleshy parts of the fruits of plants in the genus Capsicum. The seeds themselves do not produce any capsaicin, although the highest concentration of capsaicin can be found in the white pith of the inner wall, where the seeds are attached.The seeds of Capsicum plants are dispersed predominantly by birds. In birds, the TRPV1 channel does not respond to capsaicin or related chemicals, but mammalian TRPV1 is very sensitive to it. This is advantageous to the plant, as chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, whereas mammals have molar teeth that destroy such seeds and prevent them from germinating. Thus, natural selection may have led to increasing capsaicin production because it makes the plant less likely to be eaten by animals that do not help it disperse. There is also evidence that capsaicin may have evolved as an anti-fungal agent. The fungal pathogen Fusarium, which is known to infect wild chilies and thereby reduce seed viability, is deterred by capsaicin, which thus limits this form of predispersal seed mortality.
The vanillotoxin-containing venom of a certain tarantula species '' activates the same pathway of pain as is activated by capsaicin. It is an example of a shared pathway in both plant and animal anti-mammalian defense.
Uses
Food
Because of the burning sensation caused by capsaicin when it comes in contact with mucous membranes, it is commonly used in food products to provide added spiciness or "heat", usually in the form of spices such as chili powder and paprika. In high concentrations, capsaicin will also cause a burning effect on other sensitive areas, such as skin or eyes. The degree of heat found within a food is often measured on the Scoville scale.There has long been a demand for capsaicin-spiced products like chili pepper, and hot sauces such as Tabasco sauce and Mexican salsa. It is common for people to experience pleasurable and even euphoric effects from ingesting capsaicin. Folklore among self-described "chiliheads" attribute this to pain-stimulated release of endorphins, a different mechanism from the local receptor overload that makes capsaicin effective as a topical analgesic.
Research
A capsaicin transdermal patch for the management of this particular therapeutic indication was approved in 2009, as a therapeutic by both the U.S. Food and Drug Administration and the European Union. One 2017 review of clinical studies found, with limited quality, that high-dose topical capsaicin compared with control provided moderate to substantial pain relief from post-herpetic neuralgia, HIV-neuropathy, and diabetic neuropathy.Although capsaicin creams have been used to treat psoriasis for reduction of itching, a review of six clinical trials involving topical capsaicin for treatment of pruritus concluded there was insufficient evidence of effect.
Low-quality evidence indicates that oral capsaicin may decrease LDL cholesterol levels moderately.
Pepper spray and pests
Capsaicinoids are also an active ingredient in riot control and personal defense pepper spray agents. When the spray comes in contact with skin, especially eyes or mucous membranes, it produces pain and breathing difficulty in the affected individual.Capsaicin is also used to deter pests, specifically mammalian pests. Targets of capsaicin repellants include voles, deer, rabbits, squirrels, bears, insects, and attacking dogs. Ground or crushed dried chili pods may be used in birdseed to deter rodents, taking advantage of the insensitivity of birds to capsaicin. The Elephant Pepper Development Trust claims that using chili peppers as a barrier crop can be a sustainable means for rural African farmers to deter elephants from eating their crops.
An article published in the Journal of Environmental Science and Health, Part B in 2006 states that "Although hot chili pepper extract is commonly used as a component of household and garden insect-repellent formulas, it is not clear that the capsaicinoid elements of the extract are responsible for its repellency."
The first pesticide product using solely capsaicin as the active ingredient was registered with the U.S. Department of Agriculture in 1962.
Equestrian sports
Capsaicin is a banned substance in equestrian sports because of its hypersensitizing and pain-relieving properties. At the show jumping events of the 2008 Summer Olympics, four horses tested positive for capsaicin, which resulted in disqualification.Irritant effects
Acute health effects
Capsaicin is a strong irritant requiring proper protective goggles, respirators, and proper hazardous material-handling procedures. Capsaicin takes effect upon skin contact, eye contact, ingestion, and inhalation. The in mice is 47.2 mg/kg.Painful exposures to capsaicin-containing peppers are among the most common plant-related exposures presented to poison centers. They cause burning or stinging pain to the skin and, if ingested in large amounts by adults or small amounts by children, can produce nausea, vomiting, abdominal pain, and burning diarrhea. Eye exposure produces intense tearing, pain, conjunctivitis, and blepharospasm.
Treatment after exposure
The primary treatment is removal of the offending substance. Plain water is ineffective at removing capsaicin. Capsaicin is soluble in alcohol, which can be used to clean contaminated items.When capsaicin is ingested, cold milk may be an effective way to relieve the burning sensation due to caseins in milk, and the water of milk acts as a surfactant, allowing the capsaicin to form an emulsion with it.
Weight loss and regain
As of 2007, there was no evidence showing that weight loss is directly correlated with ingesting capsaicin. Well-designed clinical research had not been performed because the pungency of capsaicin in prescribed doses under research prevented subjects from complying in the study. A 2014 meta-analysis of further trials found weak evidence that consuming capsaicin before a meal might slightly reduce the amount of food consumed, and might drive food preference toward carbohydrates.Peptic ulcer
One 2006 review concluded that capsaicin may relieve symptoms of a peptic ulcer rather than being a cause of it.Death
Ingestion of high quantities of capsaicin can be deadly, particularly in people with heart problems. Even healthy young people can suffer adverse health effects like myocardial infarction after ingestion of capsaicin capsules.Mechanism of action
The burning and painful sensations associated with capsaicin result from "defunctionalization" of nociceptor nerve fibers by causing a topical hypersensitivity reaction in the skin. As a member of the vanilloid family, capsaicin binds to a receptor on nociceptor fibers called the vanilloid receptor subtype 1. TRPV1, which can also be stimulated with heat, protons, and physical abrasion, permits cations to pass through the cell membrane when activated. The resulting depolarization of the neuron stimulates it to send impulses to the brain. By binding to TRPV1 receptors, capsaicin produces similar sensations to those of excessive heat or abrasive damage, such as warming, tingling, itching, or stinging, explaining why capsaicin is described as an irritant on the skin and eyes or by ingestion.Clarifying the mechanisms of capsaicin effects on skin nociceptors was part of awarding the 2021 Nobel Prize in Physiology or Medicine, as it led to the discovery of skin sensors for temperature and touch, and identification of the single gene causing sensitivity to capsaicin.
History
The compound was first extracted in impure form in 1816 by Christian Friedrich Bucholz.In 1873 German pharmacologist Rudolf Buchheim and in 1878 the Hungarian doctor Endre Hőgyes stated that "capsicol" caused the burning feeling when in contact with mucous membranes and increased secretion of gastric acid.
Capsaicinoids
The most commonly occurring capsaicinoids are capsaicin, dihydrocapsaicin, nordihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin.Capsaicin and dihydrocapsaicin are the most pungent capsaicinoids. Nordihydrocapsaicin, homocapsaicin and homodihydrocapsaicin are about half as hot.
There are six natural capsaicinoids. Although vanillylamide of n-nonanoic acid is produced synthetically for most applications, it does occur naturally in Capsicum species.
| Capsaicinoid name | Typical relative amount | Scoville heat units | Chemical structure | |
| Capsaicin | CPS | 69% | 16,000,000 | |
| Dihydrocapsaicin | DHC | 22% | 16,000,000 | |
| Nordihydrocapsaicin | NDHC | 7% | 9,100,000 | |
| Homocapsaicin | HC | 1% | 8,600,000 | |
| Homodihydrocapsaicin | HDHC | 1% | 8,600,000 | |
| Nonivamide | PAVA | 9,200,000 |