New Research Using Electronic Taste Perception (the “e-tongue”) Explores Ayurvedic Rasas (“tastes”) Science Update by Guido Masé, December 6, 2016

Ayurveda, the “science of life” and traditional healing system of the Indian subcontinent, is perhaps the oldest formal medical system on the planet. Some of its seminal texts may date back over 4,000 years. As is the case with most traditional medicine, Ayurveda relies on an exquisite understanding of how human sensory perception and keen observation can be used to understand patterns of health and disease, as well as assess the therapeutic potentials of substances such as plants, animals, mushrooms and minerals.

One of the important concepts in Ayurveda is rasa, loosely translated as “taste”. A substance’s rasa is how it tastes and feels to us when we put it in our mouths, chew, swallow, and experience it. The taste framework described by the rasas is similar to our modern understanding of taste, though there is little attention given to the “umami” taste in Ayurveda, and “astringency” (normally thought of as an element of mouthfeel) gets more prominent placement. The Ayurvedic tradition recognizes that the taste of a substance conveys an objective and perceptible attribute of that substance which accurately and consistently represents its elemental composition and therapeutic potential.1 That is to say, similar tastes mean similar energetics and, in all likelihood, similar effects.

e-tongue flavors

 

What gets interesting is that the link between taste and medicinal effect doesn’t necessarily imply identical chemistry at the molecular level. When two substances have similar rasa, they can be similar in effect even if their chemical constituents are wholly dissimilar. For example, a few years ago an acrid, anti-inflammatory substance called oleocanthal was isolated from olive oil.2 It’s responsible for the burning feeling you experience in the back of the throat from tasting good quality oil, and it also seems to be able to reduce inflammation in a way that’s similar to conventional over-the-counter drugs like aspirin and ibuprofen. Now, despite oleocanthal having a very different structure, its acrid taste is very similar to that of ibuprofen. This has been documented by subsequent research speculating that the similarity in taste is connected to the ability of different molecules to bind to specific enzyme and receptor sites: the enzyme binding links the medicinal activity, and the receptor sites link the taste3 (both enzymes and receptors are protein structures with the ability to bind to multiple molecular substrates).

While it’s neat to realize that similar medicinal activity often means similarity of taste, the implication goes beyond simple novelty. The fact is that today, most chemical analysis machinery is geared towards identifying specific molecules: whether we’re talking about chromatography or mass spectrometry, it’s molecules we’re characterizing, not medicinal effects. This is true of even broad-spectrum “fingerprints” of plants or botanical extracts: the fingerprint changes in response to the molecular soup, not in response to potential medicinal benefits. But human taste perception, because it relies on a cocktail of molecules actually binding with protein-based taste receptor sites and the brain integrating that information into a subtle and multifaceted flavor profile, represents the interaction between substance and life form: in short, it represents a medicinal effect and not a chemical fingerprint. This is a different and powerful tool. The chemical fingerprints of oleocanthal and ibuprofen are quite different. Their tastes are very similar. Which assessment technique would you pick to guess at potential health benefits? Taste seems to be the better choice.4

So it came to be that, because humans are tinkerers, researchers developed an electronic version of the human tongue. Using a series of specialized detectors, it generates an electrical voltage in response to different taste stimuli, and produces a graph of a substance’s overall flavor profile. The detectors were difficult to make, especially those for the bitter, sweet, and fatty flavors. But in the end, scientists employed a concept very similar to that of the human body: create a membrane (like a cell membrane) of lipids and layer it onto a tangle of PVC and plasticizers tuned to a specific subset of molecules. By changing the plastic layer, making it more or less porous to different types of molecules, researchers made different membranes that are sensitive to broad classes of molecules (like bitter principles) – and only those molecules.5 [figure 1]

Tongue Detecting Flavor

Now, the research is coming full circle, and electronic tongues are analyzing traditional Ayurvedic remedies. Scientists at the Indian Institute of Medical Sciences in New Delhi sampled a total of seven plants from three taste categories: Tribulus terrestris (aerial part), Vitis vinifera (fruit) and Glycyrrhiza glabra (root) from sweet category; Piper longum (fruit), Cuminum cyminum (seed) and Capsicum annum (fruit) from pungent group; Emblica officinalis (fruit) with five rasa except that of salt but with a predominance of sour taste. They used electronic tongues and also chemical fingerprinting to generate a comprehensive picture of each botanical.6 The conclusion, of course, was that the e-tongue provided invaluable insight into the identity and medicinal activity of the botanical, while also matching up well with the traditional rasa-based descriptions that human beings gave. [figure 2]

Sensor Output vs. Concentration

In the end, I can’t help but return to the wonder that is the human body, and specifically the human tongue. It’s exciting to me to realize that our tongues are able not only to identify chemistry, but that very ancient, taste-based energetic descriptions of therapeutic herbs gives more insight into their medicinal potential than any chemical analysis ever could. To tap in to this, you can cobble together an e-tongue of your own (good luck). Or, you can do what herbalists have always done: avoid the pills and capsules, and taste your herbs. The power is on the tip of your tongue.

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  1. Rastogi, Sanjeev. “Building bridges between Ayurveda and modern science.” International journal of Ayurveda research 1.1 (2010): 41.
  2. Beauchamp, Gary K., et al. “Phytochemistry: ibuprofen-like activity in extra-virgin olive oil.” Nature 437.7055 (2005): 45-46.
  3. Joshi, Kalpana, Alex Hankey, and Bhushan Patwardhan. “Traditional phytochemistry: identification of drug by ‘Taste’.” Evidence-based Complementary and Alternative Medicine 4.2 (2007): 145-148.
  4. Baldwin, Elizabeth A., et al. “Electronic noses and tongues: Applications for the food and pharmaceutical industries.” Sensors 11.5 (2011): 4744-4766.
  5. Tahara, Yusuke, and Kiyoshi Toko. “Electronic tongues–A review.” IEEE Sensors Journal 13.8 (2013): 3001-3011.
  6. Jayasundar, Rama, and Somenath Ghatak. “Spectroscopic and E-tongue evaluation of medicinal plants: A taste of how rasa can be studied.” Journal of Ayurveda and Integrative Medicine (2016).

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