What Makes a Hot Pepper So Hot?

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Habanero peppers are rather mild by today's standards.

Habanero peppers are rather mild by today’s standards. Image by Hans.

Spicy peppers can provide culinary delight, or gastronomical torture for those with sensitive stomachs. So what is it – from a chemistry perspective – that makes those hot peppers so hot?

Capsaicin in Hot Peppers

For simplicity’s sake, we’ll limit the scope of this article to a single hot pepper constituent: capsaicin (IUPAC chemical name, (E)-N-[(4-Hydroxy-3-methoxyphenyl)methyl]-8-methylnon-6-enamide).

Scientists assign capsaicin in pure form a Scoville heat value of 16,000,000.

The Scoville value is subjective. Raters determine heat by means of tasting increasing dilution of pepper solutions.

The jalapeño pepper, for example, possesses a Scoville rating of up to 4,000, while a habanero pepper rates at about a 250,000 on the scale.

By comparison, a ghost pepper has a rating of up to 1,000,000. Hot enough?

Still hotter is the Carolina Reaper, registering an amazing 1,500,000 to 2,000,000 Scoville units.

What is it about such peppers that “turns on” the heat?

Before we answer that, let’s briefly discuss the chemistry of capsaicin.

The primary heat ingredient in hot peppers, capsaicin.

The primary heat ingredient in hot peppers, capsaicin. Image by Arrowsmaster.

What is Capsaicin?

The pungent organic (carbon-based) compound, capsaicin, is essentially a vannilylamine molecule (related to vanilla) combined with 8-methyl-6-nonenoic acid to form the amide.

To the uninitiated, this would seem a combination unlikely to result in an intensely hot taste, as vanilla is not hot – but to the chemist, it makes perfect sense.

Structurally, the chemically reactive groups within a molecule of capsaicin include ether (–COC–) , alcohol (–OH), amide (–CONH₂–) and alkene (–C=C–) linkages.

A component of capsaicin: 8-methyl-6-nonenoic acid - image by author.

One of two components of capsaicin: 8-methyl-6-nonenoic acid. Copyright image by Vincent Summers, all rights reserved.

What gives this simple chemistry so powerful a taste is capsaicin’s reaction with so-called transient receptor potential channel sensors (TRP) – in particular, the TRPV1 sensor.

TRP Channel Sensors

TRPV1 is sensitive to certain chemicals, most notably the vanilloids (compounds resembling vanilla – hence the V in TRPV1). TRPV1 is a cationic (positively charged ions) channel sensor; an algogenic (pain-producing) protein.

It functions as a polymodal sensor, meaning there is more than one way the sensation of pain originates. Excessive temperature triggers pain. So too, does the ordinarily non-damaging stimulant capsaicin. The pain that the capsaicin produces is mediated somewhat by an influx of extracellular calcium ions.

Research is ongoing to discover all of the nuances of this relationship.

Vanillylamine

Vanillylamine is a vanilloid (related to vanilla). Image by Edgar 181.

Does Capsaicin Enhance Flavor or Serve as a Warning?

Since capsaicin does not ordinarily damage the body, but in great excess can kill an organism, the question arises, is the capsaicin and TRPV1 mechanism designed to warn us that hot peppers are dangerous, or is it merely to inform us when we’ve achieved the correct flavor?

We might best answer this question by considering the additional question: Are there any advantages to including capsaicin in our diet?

Benefits of Consuming Capsaicin

There appear to be a number of health benefits from the responsible eating of capsaicin-containing food.

Hot peppers are helpful in reducing heart rate, blood clotting, insulin level, and free radicals. This is because hot peppers are rich in vitamins, minerals, fiber, phytochemicals, and antioxidants.

Additionally, a good healthy dose of peppers can help regulate body weight by lowering appetite, raising body temperature, and burning fat calories.

Curiously, although capsaicin is best known for its ability to inflict pain, when made into an analgesic cream, it has actually been used in the reduction of pain, such as that experienced by arthritics and post-operation patients.

Capsaicin: Beneficial and Chemically-Interesting Substance

Capsaicin may be the hottest part of your next meal – even if the dish is served cold. This interesting chemical can soothe arthritis pain as well as spice up a curry – and it’s all due to a chemical structure that’s related to vanilla, of all things.

Chemistry: It’s what’s for dinner.

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