Capsaicin
At some point we’ve all eaten something a little too spicy for our liking. How do you relieve the burning sensation in your mouth? Everyday Chemistries is here to help! Learn about capsaicin, the active chemical behind spicy food.
Capsaicin is the reason why hot peppers are called hot peppers, it is the chemical responsible for food tasting spicy. Capsaicin is an organic molecule that is found in well known plants like jalapeno peppers, cayenne peppers and numerous other chili peppers. It is naturally produced as a defense mechanism in plants: the burning or hot sensation produced by capsaicin is meant to deter animals from eating the plant. Ironically, not only are humans undeterred by capsaicin, we purposely add it to our food!
Contrary to popular belief, capsaicin is contained within the membrane that holds the seeds in chili peppers, not in the actual seeds themselves. The spiciness of a pepper is quantified by the Scoville Scale, which is a scale used to describe how much capsaicin is inside a pepper. The Scoville Scale was invented by a pharmacist by the name of Wilbur Scoville. Wilbur would dilute chili pepper extract in sugar water and ask volunteers if the drink was spicy. Depending on how many milliliters of sugar water was required for volunteers to report that the drink wasn’t spicy, the pepper was given a rating on the Scoville Scale (i.e. 1000 mL of sugar water = 1000 Scovilles.) Today, chemical instruments determine exactly how much capsaicin there is in hot peppers and report the concentration on the Scoville Scale.
When you eat capsaicin, you immediately feel the burning sensation on your tongue. The capsaicin molecule has a unique size and shape which allows it to interact with a receptor on your tongue called the TRPV1 Receptor. This interaction stimulates a chemical response in your body. Calcium ions will rush to the receptor triggering neurons to be released. Neurons are specialized cells in the body that communicate messages to the brain. As the TRPV1 Receptor is triggered, neurons tell your brain to feel a burning or spicy sensation in your mouth. The number of receptors in one’s mouth and the sensitivity of these receptors varies from person-to-person which is why there is a wide array of spice tolerances. Repeated exposure to capsaicin will increase the amount required to trigger the TRPV1 Receptor which is why people can build their tolerance to spice over time.
A common reaction to eating capsaicin is the desire to drink something - but should you drink milk or water? Well let’s take a look at the capsaicin molecule. It is made up of Hydrogen, Carbon, Nitrogen and Oxygen. These elements share electrons as part of a covalent bond. The negatively charged electrons are shared equally across the molecules and as a result, the molecule as a whole doesn’t have an electrostatic charge. This makes capsaicin a non-polar molecule. Like capsaicin, milk is also composed of non-polar molecule called casein proteins. Water on the other hand is composed of Hydrogen and Oxygen. Oxygen will hog the negatively charged electrons in the bond between Oxygen and Hydrogen. This gives Oxygen a partial negative charge and Hydrogen a partial positive charge. Since the electrons are not distributed equally in a water molecule, it is called a polar molecule.
This is the Capsaicin Molecule! Interact with the model to see what the molecule looks like.
This is part of a Casein Molecule! Interact with the model to see what the molecule looks like.
This is Water! Interact with the model to see what the molecule looks like.
This leads us to a very important concept in chemistry: like dissolves like. Non-polar molecules will only dissolve other non-polar molecules and polar molecules will only dissolve other polar molecules. Because of this phenomenon, the casein in milk will dissolve the capsaicin, removing it from the receptor and hence halting the burning sensation perceived by the brain. Water, being polar, cannot dissolve capsaicin and therefore cannot effectively relieve the spicy sensation. If anything, water will help spread capsaicin all over your mouth only making the spicy sensation worse. So always opt for milk or ice cream when eating spicy food - resist the urge for water!
Once you’ve ingested capsaicin, there is the dreaded aftermath a few hours later. Our bodies do not efficiently digest capsaicin. The chemical doesn’t get broken down by our digestion system so we end up excreting the chemical whole. Unfortunately for us, the same TRVP1 receptors that exist in the mouth also exist on our rear end. This explains the wildly uncomfortable burning sensation accompanied with excreting capsaicin. Fortunately, some people actually express a VR1 gene variant that aids in digesting capsaicin and can successfully break down the molecule.
So what have we learned? Although capsaicin deters garden pests such as squirrels and rabbits, humans enjoy it in cuisines around the world. The Scoville Scale measures the amount of capsaicin in a pepper. Your mouth is not actually on fire when you eat hot food, capsaicin is just triggering a response from your brain. Because capsaicin is nonpolar, drink milk to relieve your pain, not water. And finally, with respect to the VR1 gene variant, we learned that some people are just luckier than others.