Taste Technologies: Sweetness versus Savoriness

Adlai Nelson

If you were asked to distinguish between cheese and chocolate, I doubt there would be much difficulty—if someone replaced your Hershey’s square on a s’more with a slice of Gouda, you would notice right away.

While the distinction between sweet and savory may seem quite obvious, the science is surprisingly similar—and yet complicated. Right now, researchers see the divide between these tastes as thinly balanced between two amino acids in particular: glutamate and aspartate. This post is the first of a three-part series, I which I explore the history and science of these two seemingly “opposite” taste experiences—savory (umami) and sweet—and their relationship to the two amino acids listed above. I’m curious about what the history of two common food additives, monosodium glutamate (MSG) and aspartame, can teach us about how small variations between structure can affect the taste perception of sweet and savory.

Before I get to the subtle (yet important) differences between sweet and savory tastes, let’s establish how our bodies are currently understood to taste at all. Let’s consider this scenario: you’re smelling your grandma’s freshly baked chocolate cookies. “Taste” proper does not actually begin with mastication (chewing), but rather in the combination of the olfactory and gustatory cortexes. In everyday English, that means what you smell now can affect what you taste later. That sweet, homey aroma flooding your nose and making you drool is part of the complex chemosensory relationship between taste and smell (see Taste perception, associated hormonal modulation, and nutrient intake). Olfactory nerves, stimulated by this sugary bouquet, flood your brain with “signals” that in turn relay information to the gustatory (taste) cortex. So before you even begin indulging grandma’s secret recipe, your body is already preparing for what’s to come based on smell alone (See Food-Related Odors Activate Dopaminergic Brain Areas). When you finally satisfy your cravings, gustatory cells clustered on your taste buds send information to your brain once again (See Taste perception, associated hormonal modulation, and nutrient intake) and you perceive sweetness.

It is here on the taste buds where “flavor” begins. Umami and sweetness are perceived by Type II G-proteins coupled cells in the gustatory complex of the mouth. On these cells, families of taste receptors (TAS1Rs) perceive different sensations. There are three types of these heterodimer TAS1Rs: TAS1R1, TAS1R2, and TAS1R3. Savory (umami) tastes are sensed by both TAS1R1 and TAS1R3, while sweetness is perceived by TAS1R2 and TAS1R3. In a study dealing with mice that lack TAS1R3 (the taste receptor for both umami and sweetness), signs of  perception for both umami and sweetness existed, hinting that the separate taste receptors (TAS1R2 and TAS1R1) were specific for umami and sweetness (See The endocrinology of taste receptors). A recent study on rats without the required transient taste receptors and calcium modulators for sweetness and umami also revealed the importance of ATP in both umami and sweetness perception. Type II cells communicate taste to the gustatory cortex via ATP release, which helps increase enteroendocrine (in this case that means taste receptors inside the gut) hormone release that can cause changes in appetite and satiety. What is interesting to note here is that the perception of and response to sweet and savory tastes are almost identical.

So why are umami and sweetness so different? What is it about the glutamate in MSG and the aspartic acid in aspartame make them taste so different? The beginning of this answer is found in the TAS1R1 and TAS1R2 receptors. If we examine the structure of aspartate (a component of aspartame) and glutamate (a component of MSG), we would find the difference between these two acidic compounds is as small as an extra methylene on glutamate. No big deal, right? In fact, in the molecular world, a carbon and two hydrogen can greatly affect orientational binding in corresponding receptors—a small difference in structure makes a big difference in how a molecule affects the body. As found in the study above, TAS1R1 is responsible for the umami taste. The TAS1R1 and TAS1R3 receptors in a heterodimeric formation (this means these two receptors combine and work together in a one collective unit) can bind specifically to L-glutamine, which is the foundational amino acid in MSG and umami-tasting foods (See Glutamine Triggers and Potentiates Glucagon-Like Peptide-1 Secretion by Raising Cytosolic Ca2+ and cAMP).

In a recent study on Old World Monkey, researchers demonstrated that TAS1R2 coupled with TAS1R3 was the heterodimer required to perceive sweetness in both natural and artificial sweeteners. The same study demonstrated that aspartame specifically interacted with the “Venus Flytrap Module” (insert plain English translation) of TAS1R2 receptors. This complex binding is still being researched, yet it appears to act in the same way as a fly landing on a Venus Flytrap. Aspartate can interact with TAS1R2, which then binds and “closes,” sending “sweetness” signals to the brain. Both TAS1R1 and TAS1R2, however, remain a puzzle to researchers.

So I’m not the only one with questions left about savoriness, sweetness, and taste perception in general. How exactly taste receptors coordinate to the brain continues to be researched. Yet what has been found is that small differences in molecular structure have a big impact on taste. Glutamate and aspartate are practically the same amino acid, but each one relays a different taste perception to the brain. For now, it is clear that in food there is much more that meets the eye (and the tongue for that matter!).

References to check out!

Calvo, S. S. C., & Egan, J. M. (2015). The endocrinology of taste receptors. Nature Reviews Endocrinology11(4), 213.

Loper, H. B., La Sala, M., Dotson, C., & Steinle, N. (2015). Taste perception, associated hormonal modulation, and nutrient intake. Nutrition reviews73(2), 83-91.

Sorokowska, A., Schoen, K., Hummel, C., Han, P., Warr, J., & Hummel, T. (2017). Food-related odors activate dopaminergic brain areas. Frontiers in human neuroscience11, 625.

Tolhurst, G., Zheng, Y., Parker, H. E., Habib, A. M., Reimann, F., & Gribble, F. M. (2011). Glutamine triggers and potentiates glucagon-like peptide-1 secretion by raising cytosolic Ca2+ and cAMP. Endocrinology152(2), 405-413.

 

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Umami the new secret to in-flight menu success

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Photograph by Ruth Fremson for The New York Times

In March, major news outlets covered airline management buzz around umami having a unique taste property: for some reason, it still works right at 35,000 feet.

According to the New York Times piece, “At high altitudes, only umami — the pleasant, savory “fifth” taste beloved by Japanese chefs — is enhanced for reasons that are not entirely clear. So Bloody Marys, which contain the umami-rich tomato and Worcestershire sauce, taste far better in the sky than on the ground. It’s the most consumed cocktail on passenger flights, airlines say.”

Charles Spence is an expert in how different sensory mechanisms interact with one another. He speculates that the noise on the plane, even at 80-85 decibels (“quieter than in a New York restaurant”), stresses out our inner cave(wo)man:

“When faced with predators or during stressful situations, our ancestors may have turned to umami, which prompts dollops of saliva, ‘in order to get the energy to fight or flight.'”

Combine that with humidity lower than most deserts, and low atmospheric pressure, and our smell mechanisms (which make up a big part of ‘flavor’ – or what most of us call ‘taste’) just don’t respond the way they do on the ground, according to taste expert Peter Barham of the University of Bristol…

Read the full article here: Airlines Aim to Trick Your Taste Buds at 30,000 Feet

(Article originally published March 1, 2017 on nytimes.com)

Additional links:

LA Times – Palate pleasers at 30,000 feet

National Post – From opulence to budget, why is airline food so universally terrible and consistently disappointing?

The Boston Globe – Experts share their recipes for good food — and wine — at altitude

The Economist – What to drink at 30,000 feet

Runwaygirlnetwork.com – It’s all about umami for these airline specialty beverages

 

 

 

“The Hippies Have Won”

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Photograph by Cole Wilson for the New York Times.

“Consider granola: The word used to be a derogatory term. Now it’s a supermarket category worth nearly $2 billion a year. Kombucha was something your art teacher might have made in her basement. The company GT’s Kombucha brews more than a million bottles annually and sells many of them at Walmart and Safeway. And almond milk? You can add it to your drink at 15,000 Starbucks locations for 60 cents.”

In her recent piece for the New York Times, Christine Muhlke walked us through the quirky, healthy, and undeniably hipster food trends that have flooded Instagram feeds and modish restaurant scenes across the country. The idea that these trends stem from advances in nutrition science (e.g. newfound understanding of the human microbiome informing the popularity of fermented foods) fits in with our hypothesis that the molecularization of taste has validated the acceptance of “umami-rich flavors” as a dietary staple.

Read the full article here: “The Hippies Have Won”

(Article originally published April 4th, 2017 on nytimes.com)

Penguins Can’t Taste Umami. Eat Fish Anyway.

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Image ID: corp2417, NOAA Corps Collection, Photographer: Giuseppe Zibordi, Credit: Michael Van Woert, NOAA NESDIS, ORA [Public domain], via Wikimedia Commons

Who doesn’t love reading about penguins?

In the seemingly random fashion of the internet, this study out of the University of Michigan was recently picked up by another blog (ValueWalk.com), where the above image featured. We think it’s interesting.

Original U Michigan coverage of the study findings are excerpted here:

“ANN ARBOR—A University of Michigan-led study of penguin genetics has concluded that the flightless aquatic birds lost three of the five basic vertebrate tastes—sweet, bitter and the savory, meaty taste known as umami—more than 20 million years ago and never regained them.

Because penguins are fish eaters, the loss of the umami taste is especially perplexing, said study leader Jianzhi “George” Zhang, a professor in the U-M Department of Ecology and Evolutionary Biology.

“Penguins eat fish, so you would guess that they need the umami receptor genes, but for some reason they don’t have them…”

Read the whole article here: “Sweet, bitter, savory: penguins lack three of the five basic tastes”

Breaking down Ramen noodles, literally

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(Image from YouTube video made by Stefani Bardin)

USA Today College

By LaTonya Darrisaw

“After a long day of classes, Macon State College senior Kristina Whitaker does not always have time to prepare a big, healthy meal. For at least two or three nights a week, her go-to food is Ramen noodles.

‘As a full-time college student, money and time are major issues that you have to deal with and buying packages of noodles are cheap,” Whitaker said. “They fill you up and are great when you are constantly on the go and have deadlines to meet…'”

Read the rest of the story: Breaking down Ramen noodles, literally