Tag Archive for: taste receptors

Savoring the Science of Salty and Sweet

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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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Gymnemic Acid

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Photo Credits: (flickr/ mutolisp)

Photo Credits: (Flickr/ mutolisp)

Attendees of our Science of Pie event this past spring probably remember sampling gymnemic acid. For anyone who has never tried the bizarre substance, we describe here our first experience with it. Guest speaker Dave Arnold (Founder of the Museum of Food and Drink, and host of the radio show Cooking Issues), supplied everyone in the audience with a small capsule filled with a dusty green powder along with a strawberry, a sugar packet, and small amount of honey. He then instructed everyone to coat the surface of his or her tongue with the mysterious green powder, let it dissolve, and then swallow it. After the unpleasant herbal taste faded away, Arnold told the audience to empty the small sugar packet into his or her mouth. Now, sugar is usually the key to sweet desserts and happiness. But to anyone with a gymnemic-acid coated tongue, eating sugar was like face-planting at the beach and getting a mouthful of sand. The sugar was utterly unsweet. Eating honey felt like taking a swig of thick canola oil. The strawberry became tart and acidic. As the audience quickly realized, gymnemic acid has the peculiar property of inhibiting our perception of sweetness.

Gymnemic acid is precipitated from an aqueous extract of the leaves of Gymnema sylvestre, a tree found in Central and Western India, tropical Africa, and Australia. [1] The leaves of this tree have traditionally been used in Ayurvedic medicine. In fact, the Hindi name for the plant’s derivative, gurmar, means “destroyer of sugar.”[2] Only two other plants are known to have similar taste-altering effects: Bumelia dulcifica, which makes sweet and sour substances taste bitter, and of course the miracle berry of Synsepalum dulcificum, which makes sour things taste sweet. [1]

You may think to yourself, as anyone who has eaten gymnemic acid surely has, inhibiting sweetness is a miserable idea. Why are we manufacturing capsules of this? Gymnemic acid can do more than ruin your dessert. Today it is used to treat metabolic syndrome (a group of risk factors that raise one’s risk of heart disease, diabetes, and stroke), and even malaria. Gymnemic acid is also used to promote weight loss, stimulate digestion, and suppress appetite; it is also prescribed as a diuretic, laxative, and even a snake bite antidote. Gymnemic acid may treat diabetes, as it contains substances that inhibit the absorption of sugar from the intestine and stimulate the growth of cells in the pancreas, where insulin is produced. [2]

While the precise mechanisms of gymnemic acid on taste perception have not been completely elucidated, a few investigations have quantified the effects of gymnemic acid on taste and the timescales over which it operates. To determine the extent to which gymnemic acid diminishes sweet perception, a 1999 study measured the effect of a gymnemic acid oral rinse on taste perception. Their results showed that gymnemic acid reduced the sweetness intensities of sucrose and aspartame to 14% of reported pre-rinse levels. [3] These results also shed light on the timescale of taste alteration: Over a recovery period of 30 minutes, the sweetness intensity values increased linearly to a sweetness perception of 63% of the pre-rinse levels.

Another study performed at Kyushu University in Kukuoka, Japan has also shed some light on the molecular mechanisms underlying the behavior of this odd substance on our tongues. Gymnemic acid is not a pure, unique structure, but is composed of several types of homologues, or compounds of the same general formula. According to these studies, the transmembrane domain of Taste type 1 Receptor 3 (T1R3) is the primary site of the sweet-suppressing effect of gymnemic acids. The acid is predicted to dock to a binding pocket within the transmembrane domain of T1R3. [4] These findings could assist future drug design, and could perhaps lead to the synthesize of more substances that modify receptivity of sweetness. But maybe we should enjoy the wonderful sensation of sweetness as they are.

References cited

  1. Stoecklin, Walter. “Chemistry and Physiological Properties of Gymnemic Acid, the Antisaccharine Principle of the Leaves of Gymnema Sylvestre.” Journal of Agricultural and Food Chemistry 17.4 (1969): 704-08. ACS Publications. Web. 11 Sept. 2014.
  1. “Gymnema: Uses, Side Effects, Interactions and Warnings.” WebMD. WebMD, 2009. Web. 11 Sept. 2014.
  1. Gent, Janneane F., Thomas P. Hettinger, Marion E. Frank, and Lawrence E. Marks. “Taste Confusions following Gymnemic Acid Rinse.” Chemical Senses 24.4 (n.d.): 393-403. Chemse.oxfordjournals.org. Oxford Journals, 1999. Web. 23 Oct. 2014.
  1. Sanematsu, Keitsuke, Yuko Kusakabe, Noriatsu Shigemura, Takatsugu Hirokawa, Seiji Nakamura, Toshiaki Imoto, and Yuzo Ninomiya. “Molecular Mechanisms for Sweet-suppressing Effect of Gymnemic Acids.” Jbc.org. The Journal of Biological Chemistry, 23 July 2014. Web. 11 Sept. 2014.

Elsbeth SitesAbout the author: Elsbeth Sites is pursuing her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

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Taste Tripping With Miracle Berries

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MiracleBerries

Miracle Berries (Wikimedia Commons)

Imagine eating a lemon and puckering to incredibly sour…no wait, incredibly sweet citrus syrup. Then you try some tart goat cheese, but to your surprise, it tastes like sugary frosting. An underripe pineapple? Better than candy. Salt and vinegar chips? Dessert!

This fantastical taste-changing sensation is the real-life effect of a West African fruit called Synsepalum dulcificum (Richardella Dulcifica), or the “miracle berry”, which physically alters taste receptors and causes sour foods to taste sweet.

How does this work?

The secret is a protein found in miracle berries called miraculin.

Miraculin

Miraculin Protein (Wikimedia Commons)

When a miracle berry is eaten, its molecules attach to the thousands of taste receptor cells located on taste buds lining the mouth, tongue, throat, and esophagus. Humans have at least five different kinds of taste receptors to detect five basic tastes: sweet, salty, sour, bitter, and umami. (Note that evidence in the last decade suggests that there may be additional taste receptors for lipids [1] – which may explain our natural affinity for fatty foods!) Miraculin, in particular, binds directly to the sweet-sensing taste receptor known as hT1R2-hT1R3.

The earliest scheme of miraculin-hT1R2-hT1R3 binding was based on a pH-dependent conformational change of the sweet receptor-protein complex. In this model, miraculin binds somewhere near the sweet receptor site (so there is no sweet taste at first), but at a lower pH (in sour or acidic environments), the receptor changes its shape so that miraculin can bind directly on the sweet receptor site and elicits a sweet taste [2]. That’s how miraculin causes a lemon, which creates a sour, acidic environment in your mouth, to taste so sweet!

MiraculinSour

More recent studies have found additional evidence that miraculin actually starts off directly attached to sweet receptor hT1R2-hT1R3 in neutral pH and activates it in the same place in an acidic environment. Experiments have shown that sweet receptors bound with miraculin are most responsive in acidic pH (4.8-6.5), but in general, the more sour environments lead to a greater intensity of sweet taste sensation [2]. In neutral pH (when miraculin is not activating the sweet receptors), miraculin actually has another effect: it blocks other sweeteners such as aspartame, sucrose, and saccharin, and other sweetness-inducing proteins like thaumatic and brazzein, from attaching to the hT1R2-hT1R3 receptor. Basically, miraculin claims the sweet receptor site for itself so that it can reactivate the site, allowing the magical sensations of sweetness to last for up to an hour.

MiraculinBlocksSweetReceptor

Even if miraculin can manipulate sweet taste receptors to make a lemon taste sweet, shouldn’t a lemon still taste sour? Little is currently known about whether or not miraculin actually inhibits sour taste receptors, but a neuroimaging study in 2006 has suggested that the electrical signals that transmit sour taste information diminish en route to the brain stem, and that only sweet taste signals even reach the brain for processing. In the study, participants were able to still detect both citric acid and sucrose after miraculin treatment, but the sweet taste dominated because 20% of the sourness may be suppressed at the receptor level, and most of it is suppressed in the central nervous system [3].

Miracle berries were historically used by West Africans to improve the taste of fermented bread and sour palm wine, but today’s applications may be life-changing. Miraculin is being studied as a therapy for chemotherapy patients suffering from dysgeusia, which is an unpleasant metallic taste distortion. In a 2012 pilot study, eight chemotherapy patients, who reported that most foods, including water, tasted metallic, bitter, or “spoiled”, were recruited to test the effects of miracle berries. After eating miracle berries for two weeks, patients showed substantial improvement in appetite, nutrition, and response to treatment because the miraculin either masked or eliminated the unpleasant tastes altogether [4]. In the meantime, expect to see an increased production of recombinant miraculin in transgenic fruits, booming commercial demand for miracle berries as low-calorie sweeteners, and some invites to trendy “taste tripping” miracle berry parties.

References

  1. Degrace-Passilly P, Besnard P (2012) CD36 and taste of fat. Curr Opin Clin Nutr Metab Care 15: 107–111.
  2. Koizumi A., et al. (2011) Human sweet taste receptor mediates acid-induced sweetness of miraculin. Proc. Natl. Acad. Sci. U.S.A. 108: 16819–16824.
  3. Yamamoto C, et al. (2006) Cortical representation of taste-modifying action of miracle fruit in humans. Neuroimage 33:1145-1151.
  4. Wilken M, Satiroff B (2012) Pilot study of “miracle fruit” to improve food palatability for patients receiving chemotherapy. Clinical Journal of Oncology Nursing 16:E173-E177.

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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