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Savoring the Science of Salty and Sweet

Photo Credit: Joanne Gallagher (Simple Salted Caramels Recipe/Inspired Taste)

Sea salt caramels. Hawaiian pizza. Chocolate-covered pretzels. Salt-and-chili covered mangos. Aside from being delicious snacks, what else do these delectable combinations have in common? They are all quintessential examples of the “sweet and salty” food craze that only continues to rise in popularity in the culinary world as well as the population at large. When combined, these two seemingly contradictory tastes create a unique interplay that heightens the more subtle tastes and brings new complexity to the dish.

Chaudhari, Nirupa, and Stephen D. Roper. “The Cell Biology of Taste.” The Journal of Cell Biology 190.3 (2010): 285-96. Web. 23 Nov. 2014.

Figure 1: The five basic tastes.
Photo credit: Chaudhari, Nirupa, and Stephen D. Roper. (“The Cell Biology of Taste.” The Journal of Cell Biology)

Sweet and salty are two of our five basic tastes (Figure 1). As we’ve previously discussed on the blog, taste is perceived as food is broken down into individual molecules that enter taste pores on the tongue. These molecules then interact with taste receptor cells, which in turn activate nerves that send an electrical signal to the brain to trigger taste perception[1] (Figure 2).

Kibiuk, Lydia V., and Devon Stuart. “Taste and Smell.” BrainFacts.org. 1 April 2012. Web. 10 Dec. 2014.

Figure 2: Taste receptor cells activate nerves that send an electrical signal to the brain.
Photo Credit: Kibiuk, Lydia V., and Devon Stuart. (Taste and Smell/BrainFacts.org)

When we eat, our tongues sense five basic tastes. While this may seem fairly straightforward, it turns out that these five tastes can influence each other. By studying how different pairwise combinations of taste sensations interact, scientists have sought to explain how the five tastes relate to each other on chemical, oral, and cognitive levels [4].

In the case of sweet and salty foods, let’s use an example of chocolate-covered pretzels. Pretzels are characterized by a slightly bitter taste that comes from the lye or baking soda solution the dough is soaked in before baking. (These highly alkaline solutions give pretzels their signature crunch and dark brown color [5].) When dusted with a bit of salt and covered in a layer of chocolate—presto! The pretzel transforms into a delightfully salty-yet-sweet treat without a hint of bitterness. Why does this happen? Sodium has been shown to orally suppress bitterness where it directly interferes with the perception of bitterness in taste pores, a phenomenon sometimes called ‘bitter blocking.’ Instead of directly enhancing sweetness, salt suppresses bitterness and therefore allows the more ‘favorable flavors,’ such as sweet, to shine through [6].

Scientists have also cited that our penchant for sweet and salty has evolved from our primal nutritional instincts. Because our hunter-gatherer ancestors were consistently moving to new areas and eating different plants, those with a distinguishing palate were better able to detect the differences between sweet-tasting high-energy foods and bitter-tasting poisonous foods. Our taste buds are therefore naturally wired to taste sources of energy and possible toxins [4]. This reasoning can be attributed to why we love sweet and salty – sweetness indicates carbohydrates, or energy, while salt is a necessary component in the body’s water balance and blood circulation. Therefore when the flavors are combined, the biological response is increased and our body detects the food as being extra tasty [7].

And even after you taste sweet and salty molecules on your tongue, your stomach continues to sample the molecules and send signals to your brain. This ‘post-oral signal’ can also contribute to the favorable sweet-and-salty response by forming a reward circuit increases our desire for similar tasting foods [8].

Salt’s ability to change the way we perceive taste has established it as an essential enhancer in cuisines worldwide. So the next time you reach for a sweet treat, try adding a dash of salt on top – you never know what surprises it can unearth!

References Cited

  1. Gallagher, Joanne. “Simple Salted Caramels Recipe.” Inspired Taste. 8 Dec. 2012. Web. 23 Nov. 2014.
  2. Chaudhari, Nirupa, and Stephen D. Roper. “The Cell Biology of Taste.” The Journal of Cell Biology 190.3 (2010): 285-96. Web. 23 Nov. 2014.
  3. Kibiuk, Lydia V., and Devon Stuart. “Taste and Smell.” BrainFacts.org. 1 April 2012. Web. 10 Dec. 2014.
  4. Keast, Russell, and Paul A. Breslin. “An Overview of Binary Taste-Taste Interactions.” Food Quality and Preference 14.2 (2003): 111-124. Web. 9 Dec. 2014
  5. Friedrich, Paula. “For a Proper Pretzel Crust, Count on Chemistry and Memories.” NPR. 9 Aug. 2014. Web. 10 Dec. 2014.
  6. Keast, Russell, Paul A. Breslin, and Gary Beauchamp. “Suppression of Bitterness using Sodium Salts.” Chimia: International Journal for Chemistry 55.5 (2001): 441-447. Web. 10 Dec. 2014.
  7. Stuckey, Barb. Taste: Surprising Stories and Science about Why Food Tastes Good. New York: Atria Books, 2013. Print.
  8. Vanderbilt, Tom. “Why You Like What You Like.” Smithsonian Magazine. June 2013. Web. 22 Nov. 2014.


Ashton YoonAbout the author: Ashton Yoon received her B.S. in Environmental Science at UCLA and is currently pursuing a graduate degree in food science. Her favorite pastime is experimenting in the kitchen with new recipes and cooking techniques.

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Pop Rocks and Carbonation

Photo Credit: Jamie (jamiesrabbits/Flickr)

Some might say one of life’s little pleasures is eating candy.  Those who have tried Pop Rocks, however, know that its sugary glory and dare-devilish allure warrant an entirely new adventure.  Although it appears harmless, a handful of Pop Rocks candy will set off a fizzy explosion of sugar crystals and popping noises in your mouth.  But no remorse is needed; Pop Rocks aren’t actually dangerous. (Mythbusters proves your stomach won’t explode.)

How are Pop Rocks made?

Pop Rocks were developed by scientist William A. Mitchell in 1956 with a technique patented in 1961 to create a revolutionary confection which “enclos[es] a gas within a solid matrix” [1, 2].  Essentially, Pop Rocks is made of a typical hard candy sugar solution (sucrose, lactose, corn syrup and flavoring) with the addition of one important ingredient: highly-pressurized carbon dioxide (CO2).

First, the sugar solution is heated and melted to obtain a “fusible sugar”. Pop Rocks, like most other hard candies, uses a sugar solution of sucrose, lactose, and corn syrup, because these ingredients produce candy with low hygroscopicity – which means the candy is less likely to absorb water from the surrounding atmosphere [2]. This ensures that the sweet morsels do not dissolve as easily in a humid environment; they are also less sticky and have a longer shelf life.

Just as CO2 transforms syrupy juice into soda, it will turn ordinary candy into Pop Rocks!  The way this works: CO2 at 600 pounds per square inch (psi) is mixed with the melted sugar until there is about 0.5 to 15 ml of gas per gram of sugar [1, 2].  Note that 600 psi is roughly 7 times greater than the pressure inside a champagne bottle, 20 times greater the pressure in your car tires, and 40 times greater than normal atmospheric pressure at sea level [5, 6].

Photo Credit: Wikipedia

Photo Credit: Spiff (Wikimedia Commons)

Once the CO2 is thoroughly incorporated, a process which takes anywhere from 2-6 minutes [2], the mixture is cooled and the candy hardens. Cooling is done as rapidly as possible to prevent CO2 from diffusing out of the candy, reduce hygroscopicity, and minimize crystallization, a process which makes the candy very fragile. [2]  This causes the Pop Rocks to shatter and gives the candy’s signature appearance, “mini rocks” of sugar crystals.

The result?  Small candy pieces encapsulating bubbles of high-pressure CO2. Lo, the magic of carbonation!

Photo Credit: Wikipedia

Photo Credit: Evan Amos (Wikimedia Commons)

So why do Pop Rocks pop?

When you eat Pop Rocks, the moisture and temperature in your mouth melts the candy.  The subsequent popping sounds are a result of the high-pressure CO2 bubbles being released into atmospheric pressure! But what about the crackling sensations felt in your mouth?  Why do we perceive carbonation as a fizzy, tingling flavor sensation?

In the past few years, scientists have identified that taste receptor cells can actually detect and respond to carbonation.  Specifically, sour-sensing taste receptor cells are activated in response to CO2 and are responsible for the “taste of carbonation” [3].

Photo Credit: Bart Heird (chicagobart/Flickr)

Photo Credit: Bart Heird (chicagobart/Flickr)

The Taste of Carbonation

Sour-sensing taste receptors specifically express a gene which encodes carbonic anhydrase 4, which is an enzyme that catalyzes the conversion of CO2 to bicarbonate ions (HCO3) and free protons (H+).  This enzyme is only attached on the surface of sour-sensing taste receptor cells, so when you eat Pop Rocks or drink carbonated soda, CO2 is broken down and H+ proton byproducts linger outside of the cell. Since sour-sensing taste receptors activate in response to acidic environments. Therefore, they will detect this abundance of free H+ protons and ultimately, detect the taste of carbonation [3].

(A) CO2 is broken down into HCO3- and H+ by the carbonic anhydrase 4 enzyme (B) The abundance of H+ byproducts creates an acidic environment. Through ion channels, the H+ ions enter the sour-taste receptor, which depolarizes the cell and leads to the detection of CO2 .

(A) CO2 is broken down into HCO3 and H+ by the carbonic anhydrase 4 enzyme
(B) The abundance of H+ byproducts creates an acidic environment. Through ion channels, the H+ ions enter the sour-taste receptor, which depolarizes the cell and leads to the detection of CO2 .

However, carbonation doesn’t always taste sour to us because CO2 is detected by multiple somatosensory systems in the body.  Some researchers even suggest that the tingling, burning sensations associated with the perception of carbonation can be caused by CO2 triggering pain receptors [4].

Would this mean our society’s desire for carbonated food and drink has strangely evolved against a natural aversion to experiencing pain?  Personally, I can’t hear over the loud buzzing noises of Pop Rocks in my mouth to find out…and as they say, “no pain, no gain”!

Note: Modified on September 19, 2014
The diagram illustrating taste detection of carbonation has been added in the current post.

References cited

  1. “Why do Pop Rocks pop?”   http://www.poprockscandy.com/history.html. Accessed 23 August 2014.
  2. Leon K, Mitchell W (1961) Gasified confection and method of making the same. US Patent No. US3012893 A.  Available: http://www.google.com/patents/US3012893. Accessed 20 August 2014.
  3. Chandrashekar J, Yarmolinsky D,  von Buchholtz L,  Oka Y, Sly W, et al. (2009) The Taste of Carbonation. Science 326: (5951) 443-445. doi:10.1126/science.1174601.
    Available: http://www.sciencemag.org/content/326/5951/443.full. Accessed 25 August 2014.
  4. Marziali C (2010) “Sparkling Drinks Spark Pain Circuits”. University of Southern California. http://dornsife.usc.edu/news/stories/796/sparkling-drinks-spark-pain-circuits/. Accessed 26 August 2014.
  5. “Champagne FAQ’s” http://www.champagnesabering.com/home.php?id=16. Accessed 16 September 2014.
  6. “How To Check Tire Pressure” http://www.dmv.org/how-to-guides/check-tire-pressure.php. Accessed 16 September 2014.

Eunice LiuAbout the author: Eunice Liu is studying Neuroscience and Linguistics at UCLA. She attributes her love of food science to an obsession with watching bread rise in the oven.

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Flavor without the Calories: Scientists Create a Digital Taste Simulator

Think of any task and chances are someone is developing a new mobile electronic device for it. Technologies exist that pay for your coffee, track your UV light exposure, and even drive your car, but can one also simulate flavor? With that question in mind, scientists led by Nimesha Ranasinghe at the National University of Singapore are developing a device that can scintillate your tongue with sour, bitter, salty, and sweet tastes without the use of any chemicals or actual food.

The “Tongue Mounted Digital Taste Interface” uses a two-probe system to send electrical and thermal signals to the tongue to produce taste. By altering the magnitude of the electric currentA (20 – 200 mA), frequency of electric pulsesB (50-1000 Hz), and temperature (20 – 35 °C [68 – 95°F] ), the interface changes the flavor profile and intensity the wearer experiences. For example, increasing the magnitude of the electrical current strengthens sour, bitter, and salty sensations1.

Tongue_interface

Figure 1: Schematic of the Tongue Interface1

device_tongue

Figure 2: Interface applied to tongue1

To understand how this system works, you have to first understand the anatomy of a taste bud (Figure 3).

Taste_bud

Figure 3: Diagram of a Taste Bud2.

When food enters the mouth, it is broken by chewing and mixed with saliva, which dissolves small food molecules like salts and sugars. These small molecules enter the taste pore and react with taste receptor cells. These taste receptor cells activate attached nerves, which transfer electrical signals to the brain that transmit the sensation of taste. In other words, a molecular signal is converted into an electrical one. Direct stimulation of taste receptors with electricity bypasses the need for initiating the signal using molecules and directly triggers signals to the attached nerves cells, which produce taste. This is supported by research that shows electric stimulation of the tongue alone has produced sour, bitter, and salty sensations2.

In addition to an electrode, a temperature probe was also included, as changing temperatures can trigger taste sensations. For example, a previous study found that warming the front of the tongue evoked a sweet sensation, while cooling caused a salty/sour taste3. These scientists suggested this property of taste might be part of the hard wiring of the taste bud because the reverse had been shown to occur. Temperature specific nerve cells in the mouth were shown to respond to bitter and sour substances. Therefore, if temperature receptors can respond to taste, then taste receptors may also react to temperature.

While this technology is still in its infancy, it has the potential to enhance the overall gastronomic experience. Movies, video games, and TV shows could have flavor simulators that immerse your sense of taste into their world. Alternatively, chefs might be able to share the flavors of their dish remotely with patrons in the comfort of their own homes. Whatever its ultimate use, Nimesha Ranasinghe and his team’s work challenges our expectations of how flavor can be experienced and encourages others to push the boundaries of how new technologies interact with food.

Learn more about Digital Taste Interface

http://www.nimesha.info/digitaltaste.html#dti

 

References Cited

  1. Ranasinghe, N. et al. 2012. Tongue mounted interface for digitally actuating the sense of taste. 2012 16th Annual International Symposium on Wearable Computers (ISWC): 80-87
  2. Chandrashekar, J. et al. 2006. The receptors and cells for mammalian taste. Nature 444 (7117): 288-294
  3. Plattig, K. and Innitzer, J. 1976. Taste qualities elicited by electric stimulation of single human tongue papillae. Pflugers Archive European Journal of Physiology 361(2):115–120
  4. Cruz, A. and Green, B. 2000. Thermal stimulation of taste. Nature 403 (6772): 889-892.

Footnotes

  • A altering the magnitude of the electric current: The electric current, a measure of the flow of electric charges across a surface, is measured in amperes. A portable hearing aid is powered by about 0.7 microamperes, which is 3.5 times higher than the upper range of the taste electrode.
  • B frequency the electric pulses: The frequency of electric pulses is measured in hertz, which is defined as cycles per second. It is standard for the electricity (AC current) that you receive from an outlet in the US to operate at 60 Hz.

Vince ReyesAbout the author: Vince C Reyes earned his Ph.D. in Civil Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

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Understanding Umami

Imagine taking a bite of your favorite food. Is it sweet? Salty? Does it have a sour bite or a hint of bitterness? Maybe even a touch of savory umami?

Every time we eat, our taste buds sample these five basic taste qualities. Taste receptors decorating the surface of each taste bud interact with specific molecules; the corresponding flavor sensation then gets sent to your brain. Umami receptors, for example, sense the molecule glutamate. When free glutamate in our food—either naturally occurring or from added MSG—interacts with an umami receptor, we taste a delicious savory flavor.

Although glutamate is the primary source of umami flavor, certain molecules called nucleotides can enhance the umami sensation. Because nucleotides make up the genetic material (DNA and RNA) of all living things, nucleotides are ubiquitous in many of the foods we eat. Nucleotides themselves cannot activate umami taste receptors, but they can intensify the umami sensation caused by glutamate. Intrigued by this phenomenon, scientists Ole Mouritsen and Himanshu Khandelia recently published a paper exploring how one nucleotide, guanosine-5ʹ-monophosphate (GMP), might work together with glutamate to activate umami taste receptors.

Only one of the three known umami taste receptors can interact with both glutamate and GMP. This so-called “T1R1/T1R3” receptor switches between two states: an “off” state when no glutamate is present and an “on” state when glutamate is attached to the receptor. To understand how GMP might affect these two states, Mouritsen and Khandelia ran a series of computer simulations testing the receptor’s behavior in the presence or absence of GMP. As expected, glutamate caused the receptor to exist in the “on” state more than the “off” state. When GMP was added to the simulation, both GMP and glutamate interacted with the receptor to further stabilize the “on” state.

Model of the T1R1/T1R3 umami taste receptor. The taste receptor (in blue) is “off” when no glutamate is present. Glutamate interacts with the receptor, stabilizing the “on” state and signaling an umami taste sensation. Glutamate and GMP together bind the receptor and further stabilize the “on” state, presumably leading to a longer, more intense umami sensation.

Besides providing a compelling molecular model for umami taste sensation, this and future work on taste receptors may help us become more savvy seasoners in the kitchen. Because umami taste receptors are similar to the taste receptors for sweet and bitter, understanding how molecules like GMP enhance umami sensations can help us develop enhancers for other taste sensations. Just as GMP makes glutamate taste more intensely umami, a sweet enhancer could make sugar taste sweeter with no added calories. Identifying more taste enhancing molecules like GMP could bring a whole new dimension to the way we cook in the future. Forget about salt and pepper—the flavor enhancers are coming.


ProfileImageSmallAbout the author: Liz Roth-Johnson is a Ph.D. candidate in Molecular Biology at UCLA. If she’s not in the lab, you can usually find her experimenting in the kitchen.

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