Monthly Archives: March 2016

Feelin’ Hot Hot Hot

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Are you a seeker of spice? Does the idea of “burning” your tongue with the hottest pepper in the world appeal to you? According to Guinness World Records, the current hottest pepper in called the Carolina Reaper, which clocks in at 2.2 million Scoville Heat Units.

So, first things first…does eating a pepper actually burn your tongue?

The answer is no, well at least not in the same way as hot chocolate does.

When you burn your tongue by drinking a hot substance like coffee, physical damages is being done to the taste cells in the mouth. They can get scarred or burned quite easily, and you may have noticed you have trouble tasting and that your tongue/other part of the mouth feels rough within the burned area.

However, peppers have a different operational system for getting you to “feel” the heat.

Capsaicin (full scientific name: 8-methyl-N-vanillyl-trans-6-nonenamide), the molecule that is concentrated within the placental tissue of pepper (NOT the seeds, tell your friends that new fact of the day), is source of a chili pepper’s heat.

anatomy_of_a_ jalapeno
Notice how the capsaicin glands are located in the placental tissue.

What happened when you eat items containing chili pepper?

The capsaicin molecules activate the TRPV1 receptor in a chemical fashion, which signals an influx of Na+ and Ca 2+ ions into the cell. Coincidently, this receptor is also the same one that is triggered by intense heat or a physical abrasion. So, even though one feels the sensation of burning after eating a pepper, that’s all it is – a sensation. There’s no physical burning of tongue when eating a pepper (unless you heat that pepper in a microwave and put it immediately on your tongue of course).

The mechanism behind this “burning” sensation of capsaicin is studied through chemesthesis – the chemical mechanisms by which we feel burning, cooling, and even the bubbly feeling of carbonation of foods. These sorts of sensations are classified differently because they go through different nerves, specifically the trigeminal nerve. What also makes these sensations different from your basic tastes is the way we can become desensitized to them.

First look at the following chart, which shows you not only how powerful of an irritant capsaicin is, but also how long that feeling of irritation persists.

chart
Capsaicin sensation of irritation lingers much longer than some other more common sensations from other foods.

One of the most common things studied with capsaicin is desensitization. Desensitization is the process by which you would rate something less intensely because of previous exposure to it. Experiments have showed that participants tasting a variety of capsaicin-infused samples show acute desensitization, with intervals between sample of 2.5-5 minutes and chronic desensitization, where they rate the intensity of the same sample over the course of days, with each subsequent day the intensity rating is, on average, less than before.

What’s also cool is that the intensity of the sensation is different based on exposure. Many studies have been done comparing the intensity ratings of capsaicin-fused samples from people who are frequent spicy food eater vs. people who rarely consume spicy foods.

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Notice how with both rinsing and sipping the spicy-food eaters (in red) still rate the capcaisin-infused sample as less intense than the non-consumers (in blue).

Yes, there is more to the Food Science Building than just the Creamery on the first floor. The second floor contains a variety of booths and other testing rooms where all kinds of food products and solutions are being tested. Companies and grad students alike test out their products to *paid* participants. I’ve worked in the sensory lab for about a year now, and in my time we’ve tested everything from ice cream to perogies to wine. We’re alway looking for new participants, so if you’re interested in being paid to try food, send an e-mail over to Jennifer Meengs, the coordinator of the Sensory Center, at jas138@psu.edu.

A cool experiment being conducted in the sensory food science lab here at Penn State involves the use of a capsaicin mouthwash given to non-spicy food eaters (using an intensity-matched bitter tasting mouthwash as the control). At the start of the experiment, they rate a whole bunch of different sample including sweet, salt, bitter, and yes, some that have capsaicin it them. After rinsing with the mouthwash twice every day they’ve come back to lab and again rated the same samples based on their intensity. The goal was to see the capsaicin-mouthwash participants rate samples of all the tastes, not just those with capsaicin, less intensely. The work so far is going well, and the lead researcher hopes that this work will be used to help patients with burning mouth syndrome become less sensitized.

Burning mouth syndrome is especially difficult to diagnose because the causes are most unknown. There are several “types” of burning mouth syndrome indented, with the first type having no known cause. Type II is often associated with anxiety, and Type III may be contributed by some allergies.

MSG

So if you remember in the last post we talked about the basic tastes, one of which was umami or “savory” which can best be described as the tastes of good ol’ monosodium glutamate (MSG).

Today, MSG is a flavor enhancer that can often be found in Chinese-style cooking and also a storm of controversy. Just a quick Internet search on MSG can garner stories from people suffering headaches, brain damage, and death – all attributed to MSG.

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The molecular structure of MSG.

One of the more popular “attacks” on the substance is that people are attributing it to “Chinese Restaurant Syndrome.” In this syndrome, a person experiences headaches, heart palpitations, an increase in their asthma symptoms, and chest pain.

The “discovery” of this syndrome actually began in 1968, where the term was coined by Dr. Robert Ho Man Kwok in a letter to the New England Journal of Medicine. Though a Chinese immigrant himself, he said he only ever felt the syndrome when he was eating Chinese food in America, and described a number of the symptoms listed above along with the distinct ingredients in the foods he was eating, one of them being monosodium glutamate, The journal became flooded with responses of readers sharing their own stories, and it was even picked up by The New York Times. A study was done in 1969 that injected large amounts of MSG in mice that ignited a firestorm of fear and panic because of the neurological effects on the mice.

 After that point, countless studies have been done on the effects of MSG. It’s been given to patients orally and intravenously, in small does and extremely high doses, to mice and humans, etc.

 

But let’s take a step back to figure out what we know. Monosodium glutamate is a derivative of glutamate, which we learned is an important neurotransmitter in the body. It’s an excitatory transmitter, which means its presence will cause an increase in the frequency of its nerve impulse when its being sent. Therefore an increase in heart rate wouldn’t be surprising as a potential side effect of MSG.

A lot of studies have reported that headaches increase with the consumption of MSG. A study done in 2009 by Jennifer Xiong showed that neural damage in the brain was dose dependent for MSG, meaning the higher the dose given, the more damage there was to the mature neurons. Though Xiong did not find the exact mechanism, this is what was determined to be the cause of the headaches. However, it was also found that MSG did not cause damage to glial cells or immature neurons, and the presence of Vitamin C also helped decrease the headache effects of MSG.

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One of the figures from the Xiong study. Notice how the neurons swell from their original size with the introduction of MSG.

An important thing to consider hear is the blood brain barrier, which has a low permeability to MSG. This is especially true to dietary MSG (foods naturally present with MSG, like tomatoes, vs. just being added in), so the actual amount of extra glutamate getting into your brain is small. Another thing to consider here is the actual amount of MSG an average person consumes in a day. The average dose for a person in the U.S is 0.55 g/day, but a large meal at a Chinese restaurant could have up to 3 grams, making the possibility of headaches and other symptoms more likely.

 

So what’s the verdict? Based on numerous studies, evidence of MSG sensitivity is a proven concept. Though the extent of symptoms is based on the sensitivity of the person, it takes a relatively large amount for effects to be felt. So, MSG is regarded as safe in regular amounts, but could have unpleasant when eaten in excessive amounts.

There is so much data on this topic, so it’s easy to see why people are very adamant about MSG. In one single article I read it listed various symptoms of “Chinese Restaurant Syndrome” and then gave links to studies where it was both proven and disproven for every symptom.

Basic Tastes are Anything but Basic

Ok, so now that we know that the tongue map is only a myth, let’s get to a topic that is thoroughly backed up with science- the basic tastes.

So what is a basic taste? Technically it’s a taste that one is able to distinguish through repeated tests and trials as a separate, singular taste. (So you’re clearly tasting one thing and not a combination of other tastes).

If you ask your local food/sensory scientist, they’ll be able to rattle off the five basic tastes without even thinking: sweet, salty, bitter, sour, and umami (savory). Research has shown that there may be another, but we’ll get to that later.

While the tongue maps is a bust, here’s what we do know about how these basic taste are detected all throughout the tongue. Tastants can either: flow directly through an ion channel, bind and block ion channels, or bind to a G-protein coupled receptor (GPCR).While that last sentence wasn’t the clearest the in world, hopefully this graphic will clear it up.

taste ways
This image shows how basic tastes move through a taste pore. These wouldn’t be happening all at once, but each pore will detect a single taste at a time.

In cognitive psychology, we’ve already seen an action potential before, that’s how nerve signals are transmitted throughout the body. It’s also the same way we taste sour and salty! You can remember because salts can be many ions including Na+ and Cl-, and sour tastes are acidic, so think of H+ ions. As seen on the Figure, the ions for salty and sour pass through an ion channel which causes that influx of sodium, leading to depolarization which then triggers potassium ions to move out. It is then at this point where calcium plays a role.

The tastes of sweet, bitter, and umami however go through different receptors. There are specific types of receptor depending on the taste (for example bitter is T2Rs). These receptors are held in place with the G-proteins, and after they pass through the process of depolarization starts, so the only difference is how the tastant first pass through the taste pore.

It’s important to note that serotonin, a neuromodulator we discussed, serves as a sort of intermediate transmitter to help communication between the taste pore and the rest of the taste bud.

 

So what about umami? It’s a word derived from the Japanese language, which translates into “pleasant savory taste”: umai means “delicious” and mi “taste.” (We’ll just agree that calling things “delicious” is not good scientific term”.

While savory is closest singular word to describe it, think of umami as the taste of chicken broth or a shitake mushroom. Monosodium glutamate (MSG), is also used as a descriptor for it. In addition to being in a variety of broths, the taste is also present in many Asian cuisines.

Remember how the defining characteristic of a basic taste is that it has to be distinguishable from all others? A characteristic like umami has been known in the scientific community as early at the 1910’s. However, proving that it was indeed a basic taste took some time.

Shizuko Yamaguchi helped develop this graph which shows how the taste of umami “stands on its own” and isn’t dimensionally close to the other tastes.

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The graph isn’t labeled in this case because food scientists understand that these are dimensionless axes where the points are physically separated by how different they are.

Further scientific evidence also showed that umami had its own taste receptors, further cementing its place a basic taste.

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The specific taste receptors for bitter, sweet, and umami. Notice how there numerous types of T2Ps bitter receptors.

While umami has been established, science is leading towards the discovery of another basic taste, it’s called oleogustus, the taste of fat (oleo is a Latin root meaning ‘oily’).

Out of Purdue University a study was done to see of participants could come up with words to describe the taste of fat. It was very important to the researchers that the participants didn’t confuse the texture of fat (creamy, smooth) with the taste.

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For example in a hops sorting task people would be asked to group the samples based on how they smell.

Participants were told to sort a variety of sample into different groups dependent on taste (often called a sorting task). While initially they placed the fat samples with the bitter samples, upon further testing between the fat and bitter they made a separate fatty acid group. While more research needs to be done (will they find a ‘fat’ receptor?), it’s an important step in the right direction.

Fun fact: Cordelia Running, who helped pioneer this study at Purdue, is now a post-doc in Food Science Department here at Penn State!