Biting into a spicy pepper in a chili or curry dish can be an exhilarating and occasionally painful experience. The chemical compound capsaicin --- and the chemically similar dihydrocapsaicin and nordihydrocapsaicin --- cause this distinctive burn. These chemical compounds are a part of a larger family of chemicals known as vanilloids, which are known for their strong and distinct flavors. Other types of vanilloids occur in foods such as vanilla, bay leaves and ginger.
Chemical Composition
Like all vanilloids, capsaicin has a hexagonal ring of carbon molecules and a side chain of molecules called a polar amide, which contains nitrogen, hydrogen, carbon and oxygen. The polar amide side chain prevents capsaicin from having an odor and lowers its volatility, meaning it does not break down easily. This side chain also produces the burning sensation you feel when you eat capsaicin.
Burning Sensation
When the capsaicin enters your mouth, the hydrocarbon side chain penetrates and binds to certain cell receptors. This opens the cell and allows calcium ions to enter, which in turn triggers a pain signal to your brain. This is the same reaction that happens when your cells are exposed to heat. The bond formed by the hydrocarbon side chain is strong, but it can be broken when capsaicin encounters certain chemicals. The casein protein in milk is one such chemical, and this is why drinking milk can quickly stop the burn from a hot pepper.
Negative Side Effects
While a moderate amount of capsaicin will only produce a slight burning sensation in your mouth and throat, eating it to excess can produce unpleasant side effects. High exposure can cause irritation in your mouth and throat that leads to difficulty breathing, tear production and nasal irritation. The National Pesticide Information Center estimates that orally administered capsaicin within the range of 0.5 g to 5 g per kilogram of bodyweight can lead to death in humans.
Capsaicin Content
The "Journal of Environmental Science and Health, Part B" published a comprehensive study of various pepper species in 2006, and found that peppers from the Capsicum chinense species have the greatest concentration of capsaicin in their fruit. This species includes habaneros. Peppers from the Capsicum frutescens species, such as Tabasco peppers, also scored highly for capsaicin content. Eating the capsaicin in these peppers will have a greater effect on your mouth than their milder cousins.
References
- "Journal of Environmental Science and Health, Part B"; Screening Capsicum Accessions for Capsaicinoid Content; George Antonious et al.; June 2006
- National Pesticide Information Center; Capsaicin General Fact Sheet; March 2009
- National Pesticide Information Center; Capsaicin Technical Fact Sheet; J. A. Gervais et al.; October 2008
- Frostburg State University; Fire and Spice; Fred Senese, Ph.D.
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