Spicing up Chemistry
Spices have been used in cooking since Roman times, and were believed to be important as antiparasitic agents and as gastrointestinal protectants in the diet
Capsaicin (1) is responsible for the 'hotness' of chilli peppers. Part of the molecule is structurally similar to vanillin, and so belongs to a class of compounds called vanilloids. The other part has an amide group and an extended hydrocarbon chain, making capsaicin a member of the alkylamide family. Molecules with both these parts are called capsaicinoids.
Scientists have been investigating how the body responds to chillies. In the mouth, lips, throat, tongue and nasal cavity, capsaicin binds to the membrane at the ends of nerve cells, specifically sensory neurons, where it is recognised by a specific protein (a sensory receptor) located in the membrane. They believe that this protein (TRPV1) is important in the detection of noxious stimuli, including abrasion, heat, acids, and vanilloids. TRPV1 provides a channel for Ca2+ ions. When activated by a stimulus, the channel allows Ca2+ ions into the sensory nerve cell and this causes a signal to be sent to the pain-processing centres in the brain.2 The fact that capsaicinoids bind to the receptor that responds to a thermal stimulus explains why chillies are 'hot'. The 'hot' response releases endorphins in the brain, which have pain-relieving properties similar to opiates. Maybe this is why people get addicted to curries?
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