Wednesday, March 12, 2014

Are Chilies Spicy, Hot, Or Piquant?

Biology concepts – fruit, spice, capsaicin, Scoville heat units, TRPV1 heat sensor, taste, true berry

Preface: I had intended on finishing our series on taste sense with a single post on how spicy foods are a taste exception. But the information and exceptions kept pouring out of the literature; every turn gave me a new feature to look at in more depth. So, instead of a single post, here is the first in a series on spicy foods and how our sensation of spiciness or coolness is related to many biological concepts and functions. We experience these daily without ever thinking about them, but the exceptions will show just how inventive life can be.

Here is the fruit of the jalapeno pepper. It is formed from
a single ovary, where the pericarp (ovary wall) is made up
of the exocarp, mesocarp, and endocarp. The placenta is
also called the septum, and on the sides of it are the
capsaicin glands.
Quick, name the spiciest fruit you've ever tasted. Spicy fruit? Is this some bizarre candy commercial? Nope. I bet we've all had a spicy fruit – how about jalapeno fruits, or habanero fruits?

Chili peppers are indeed considered fruits. They are true berries, but they are the exception in berries, as they don’t have a fleshy middle; they're mostly hollow. They form from a single ovary, and the chili is the entire ovary wall ripened into an edible form called a pericarp.

The capsaicin (the dominant spicy molecule in chili peppers) is present in all the fruit structures, but there are higher concentrations in the seeds and the ribs (septa) that hold the seeds to the inner face of the fruit wall. Even the hottest peppers have tastes other than spice, but it's really a matter of how much capsaicin is packed into the flesh that determines the overall sting of the pepper.

Chili peppers got the name "pepper" because they were spicy, like the black pepper plant, but there's no botanical relationship between these two kinds of plants. Chili peppers are from the genus Capsicum. There are about 27 species in the genus, but each species comes in several varieties – bell peppers and jalapenos come from the same species. The Capsicum genus is just one of the 90 or so genera in the family Solanacae, the nightshades. This is a diverse family of plants, including potatoes, tomatoes, tobacco, petunias, and even some trees.

Fusarium fungi preferentially grow on fruits. They are
the primary cause of pre-dispersal seed mortality. Humans
are susceptible to infections with the fungus, and eating
bread made from contaminated grain is lethal. In the
2000’s the US proposed using fusarium mycotoxins as
a way of killing drug crops in South America.
Why would plants make their fruits, leaves, and stems spicy? As a defense, I would guess. It seems that this discourages many an herbivorous predator. A 2008 report shows that Fusarium fungus has a hard time growing on plants that produce capsaicin, but easily infects those that do not.  The development and increase in capsaicin levels is a result of evolutionary pressures applied by fungal chili plant pathogens.

But on the other hand, why put the hot stuff in the fruits? Don’t you want animals to eat the fruits and then spread the seeds around in their feces? Isn’t that the point of making a fruit – to entice some animal to disperse your seeds? It makes one wonder.

For what ever reason they do it, there's a new king of the spicy fruits: the Carolina Reaper. Bred in South Carolina specifically to be the world’s spiciest pepper, the Reaper weighs in at a whopping 1.6 million Scoville heat units. Here is a video of some nut downing one, but be careful – there's vomiting involved. That should give you some idea of this pepper’s powerful potency.

What’s a Scoville heat unit (SHU), you ask? In the test originally designed by pharmacist Wilbur Scoville in 1912, this number referred to the number of squirts of sugar water needed to extinguish the flames in your mouth after you bite a pepper. Later, SHU became more scientifically defined as the number of dilutions needed to make a given mass of chili flesh lose its sting. But this was still a subjective measure, with different people reporting different dilutions as necessary.

Born in January 1865, Wilbur Scoville’s middle name was Lincoln,
after the President who would be assassinated later that same year.
He was a pharmacist at Parke Davis when he devised the Scoville
Organoleptic Test for hot food spice, but he was famous for other
reasons in pharmacy. He wrote several textbooks that were used up
until the 1960’s. On the right is the madness Scoville wrought. This is
the Carolina Reaper, bred only to be hot. It is grown only in one plot
in South Carolina, appropriately named Pucker Butt Farms. Notice
that the person is not wearing gloves. I really hope he didn’t rub
his eyes or pick his nose after this.
Nowadays, scientists use a laboratory test called high performance liquid chromatography (HPLC) to measure the amount of capsaicin in each sample. One part capsaicin per million parts pepper is equal to 15 Scoville units (or approximately 18 µM capsaicin/SHU). Pepper eaters agree that the HPLC method gives SHU values about 20-40% below those of the old methods.

The 1.6 million SHU for the Carolina Reaper is about 100,000 units more than the previous record holder, the Trinidad Morgua Scorpion pepper, which is still the spiciest pepper that grows in the wild. Take note that the value is the average for a batch of the peppers grown at the same time at the same place, but the SHU will vary from pepper to pepper.

For the Reaper, at least one individual pepper has been measured at more than 2.2 million SHU, and a Morgua Scorpion individual has come close to this at 2.01 million SHU. The individual differences can come from slight variations in environmental and soil conditions between plants.

A 2013 study found that temperature will affect capsaicin levels. For several pepper cultivars, as the growing temperature increased, so did the capsaicin levels. But the effect was the opposite in jalapenos; higher growing temperatures led to lower capsaicin levels.

The cause of all this spiciness – capsaicin. It's not a protein, but is more aptly described as a nitrogen containing fatty acid – yet another amazing fat. It is one of many compounds called vanilloids, named after one member, the vanillin molecule that gives us vanilla taste and aroma.

Capsaicin is an alkaloid fatty acid. The long hydrocarbon
tail makes the molecule fat soluble but water insoluble.
It also adds to the molecular weight and reduces its
volatility. This is lucky, nobody wants a snoot full of
capsaicin. Some people live for the hot food, enough to
wear it as a permanent marker on their body.
The fact that capsaicin is a fat is pertinent to eating hot peppers. Chemists say, “Like dissolves like,” meaning that a fat will be soluble in fat, but not in water. So when eating spicy foods, remember that drinking water isn’t going to douse the fire no matter how much you drink. Alcohol will work, but beer doesn’t have enough alcohol to make a difference.

The best bet to take the sting out of your curry is whole milk. Why? Because whole milk has sufficient fat to draw the capsaicin off your tongue, and milk also contains a protein called casein. Casein is lipophilic (lipo = fat, and philic = loving), so it will take the capsaicin off your tongue too. You won’t look very manly, but at least you’ll survive.

Many “professional” chili eaters don’t worry about the manly thing at all. After proving how strong they are by eating a ghost pepper or a Carolina Reaper, they will often fill their mouth with Cheez Whiz, or even shove cheesecake up their nose to try and placate their burning nasal membranes!

Pure capsaicin is rated at 16 million SHU, so even the hottest Carolina Reaper is only 1/8 as spicy as theoretically possible. Of course there is no way you could make a pepper that contains only capsaicin.  The chili with the best public relations firm is the Ghost Pepper (Bhut Jolokia) of India. The Ghost is all the rage in culinary spice these days, but it only carries a 1 million SHU warning. I wonder if your mouth can actually feel (not taste) the difference between a Carolina Reaper, a Morgua Scorpion and a Ghost Pepper. I’m not planning to investigate my question.

Habaneros range from 350,000 to 500,000 SHU, depending on the cultivar (Red Savina habaneros were developed to be hotter). Jalapenos manage only a 3500-8000 on Scoville’s scale, and I have a hard time with these!

The Mayans and Incas used chili peppers in war, especially
against the Spanish. The Incas burned chili plants to create a
burning smoke screen, while the Mayans filled gourds with
chili extract and threw them as grenades. In the 2000’s, the
Indian Defense Council considered using Ghost Peppers in
hand grenades as a riot weapon. Everything old is new again.
As little as 10 parts per million (ppm) of capsaicin brings pain to the skin, eyes, mouth or nose. This may be why capsaicin is used as pepper spray weaponry. Pepper spray come in at about 2 million SHU, so some individual Carolina Reapers have more capsaicin than pepper spray. No wonder people vomit when they eat one.

Now for a question with a seemingly easy answer, but one that opens many doors for investigation. Why do we say that spicy foods are “hot?” In culinary terms, “hotness” is made distinct from other spice characteristics by being called piquancy. Chili peppers are piquant (from Middle French for irritating or pricking), not hot. This is where we get the name of picante sauce.

The capsaicin in chili peppers causes pain in the mouth, like a burning sensation. It burns on the skin as well. And eating peppers make you sweat, just like when it is very hot. I'm guessing that this is where the term "hot food" came from. With very spicy peppers, like the reaper or the Morgua Scorpion, the amount of capsaicin brings blistering of the oral mucosa. Basically, your body is sensing a burn, and creates blisters to try and keep the burning compound away from the deeper tissue.

It's true that the closer to the equator people live, the more chili peppers they tend to eat. Believe it or not, eating peppers helps to cool you off. On a very hot day, the heat builds up in your body and you need to get rid of it. Sweating is one way we dissipate heat; the evaporation of water from the skin requires an input of energy, and this comes from the heat of the skin. The loss of heat makes you feel cooler.

We have talked about endorphins in a previous post on exercise and
mood. Pain stimulates the release of endorphins that then block the
transmission of pain signals. It would be nice if you could get the
effect without the pain. Endorphins also impart a sense of elation,
which is one reason chili eaters indulge so often and so heavily.
This is one reason people eat chili peppers. Another reason could be that people like the taste. Chilies do have taste, they aren’t just heat. But I think this a cover for eating them as an endorphin rush. Pain sensation in the body is met with an internal pain-killing cascade that includes the production of endorphins that make a person feel elated and numbs the pain. It’s like the old joke where the guy hits himself in the head with a ball peen hammer because it feels so good when he stops.

So how does eating a pepper turn into a sensation of burning and pain? You definitely transmit neural signals of pain when you are burned by heat, and this is the key. The protein on pain neurons that sense burning heat and conduct the signal to the brain to be perceived as pain – well that same protein is activated by capsaicin! The signal is the same; your brain doesn’t know the difference between activation by capsaicin and activation by scalding heat – it interprets them both as pain!

The protein responsible for this is called TRPV1, and we will have much more to say about this ion channel in the weeks to come. It's a heat sensor, a pain sensor, an acid sensor. It can create pain and inhibit pain. It can cause itch and cough, and maybe prevent cancer. Oh, and it creates vampire bats too.

González-Zamora A, Sierra-Campos E, Luna-Ortega JG, Pérez-Morales R, Rodríguez Ortiz JC, & García-Hernández JL (2013). Characterization of different Capsicum varieties by evaluation of their capsaicinoids content by high performance liquid chromatography, determination of pungency and effect of high temperature. Molecules (Basel, Switzerland), 18 (11), 13471-86 PMID: 24184818

Tewksbury JJ, Reagan KM, Machnicki NJ, Carlo TA, Haak DC, Peñaloza AL, & Levey DJ (2008). Evolutionary ecology of pungency in wild chilies. Proceedings of the National Academy of Sciences of the United States of America, 105 (33), 11808-11 PMID: 18695236

For more information or classroom activities, see:

Scoville heat scale –

Chili fruits –

Fusarium fungus –

Endorphins –