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New Research Using Electronic Taste Perception (the “e-tongue”) Explor


Ayurveda, the “science of life” and traditional healing system of the Indian subcontinent, is perhaps the oldest formal herbal medical system on the planet. Some of its seminal texts may date back over 3,000 years. As is the case with most traditional herbal medicine, Ayurveda relies on an exquisite understanding of how human sensory perception and keen observation can be used to understand patterns of health, 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” (a savory quality often associated with amino acids like glutamate) 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 may also relate to how  it is experienced in the body.1 That is to say, similar tastes mean similar qualities and, in all likelihood, similar effects.

 

What gets interesting is that the link between taste and effect does not 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 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. Now, despite oleocanthal having a different chemical structure, its bitter, acrid taste is very similar to that of salicin and other plant molecules, and it may share similar health-supporting qualities. 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 activity, and the receptor sites link the taste3 (both enzymes and receptors are protein structures with the ability to bind to multiple molecules).

While it is neat to realize that similar 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 are talking about chromatography or mass spectrometry, it is molecules we are characterizing, not physiologic 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 impacts on our body tissues. But human taste perception, because it relies on a cocktail of molecules binding with real, physiological protein-based taste receptor sites with the brain then integrating that information into a subtle and multifaceted flavor profile, represents the interaction between substance and life form: in short, taste represents an effect and not a chemical fingerprint. This presents us with a different and powerful tool. The chemical fingerprints of oleocanthal and other botanical substances like salicin from willow bark are quite different. Their tastes can be very similar. Which assessment technique would you pick to guess at potential effects? 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 


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 (Tribulus aerial part), Vitis vinifera (fruit of the grapevine) and Glycyrrhiza glabra (licorice root) from sweet category; Piper longum (long pepper fruit), Cuminum cyminum (cumin seed) and Capsicum annum (hot pepper fruit) from pungent group; Emblica officinalis (amla fruit, aka Phyllanthus emblica) 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 potential physiologic activity of the botanical, while also matching up well with the traditional rasa-based descriptions that human beings gave. 

In the end, I cannot help but return to the wonder that is the human body, and specifically the human tongue. It’s exciting 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 physiologic potential than any chemical analysis ever could. To tap into this, you can cobble together an e-tongue of your own (good luck). Or, you can do what herbalists have always done: taste your herbs by choosing powders, teas, or liquid extracts. The power is on the tip of your tongue.

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).

Updated 12/14/20 

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