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Tastes: A ‘Total’ Change

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For years together, two salient points about taste that remained etched in everybody’s memory were:

  1. There are 4 basic tastes – salty, sweet, sour and bitter;
  2. Taste receptors corresponding to each taste are located in distinct regions of the tongue.

But today, research condemns these theories as outdated. With the entry of Umami, tastes saw a ‘total’ (total both as in sum and complete) change. The numeric 4 became history and 5 the buzzword.

Umami expands as Umai – delicious and mi – taste, in Japanese lingo. To be precise, it is a meaty, savoury or brothy taste that leaves a lingering effect on the tongue. It is represented by the taste of amino acid L-glutamate and 5’- ribonucleotides Guanosine Monophosphate (GMP) and Inosine Monophosphate (IMP). The taste was discovered by the Scientist, Kikunae Ikeda, as early as 1908. But it was not until 1985 that even the term ‘Umami’ was globally accepted as a scientific word to represent the above mentioned tastes. Its rise as the fifth taste also came after a lot of debate. Studies inferred that it cannot be produced from combinations of the known tastes, and receptors detecting it (mGluR4, mGluR1, T1R1+T1R3) were present on the tongue. These facts earned umami its status as a basic taste.

Mono Sodium Glutamate or Ajinomoto-The Umami Flavour Enhancer

Mono Sodium Glutamate or Ajinomoto-The Umami Flavour Enhancer

The flavour enhancer, Mono Sodium Glutamate (MSG) more often synonymous with its brand name Ajinomoto, symbolizes this unique taste. Some common foods with this taste are:

  • Vegetables – ripe tomatoes, mushrooms, asparagus, seaweed kelp, Chinese cabbage, spinach and celery
  • Dairy product –  aged cheese like Parmesan
  • Drinks – green tea and red wine
  • Soy sauce
  • Non-vegetarian foods – fish, meat, chicken, prawn, crab, lobster

Mother’s milk, the first food during infancy, is a rich source of L-glutamate and also our maiden umami food.

Umami has a threshold of 0.03% of MSG solution. It is pleasant only within a narrow range. Umami ingredients exhibit synergism when present in tandem (L-Glutamate and GMP/IMP) in a dish. Synergism amplifies the taste 8 folds the taste of constituent umami ingredients put together. The synergy is intensified by long-slow cooking, braising, searing and roasting. Umami also impacts the perception of other tastes – it makes sodium seem saltier, sugar sweeter, sour and bitter less acerbic and biting. Some of these properties find applications in the development of health-foods and in the field of Geriatrics. Umami has made low-sodium foods a possibility; the mouth-feel and fullness it imparts has encouraged the manufacture of low-fat foods. As gustation and olfaction wane with age, addition of umami ingredients in foods enhance its taste, flavour and improve food intake of elderly people.

Tongue Map – A Delusion (Image via Wikipedia)

The tongue map (showing bitterness as sensed at the back of the tongue(1), sourness on the sides at the back(2), saltiness along the edges in the front (3) and sweetness in the tip(4)) was proved a delusion by Researcher Virginia Collings in 1974. She found that perception of taste was not spatially segregated on the tongue; any taste could be discerned in any region, that had taste receptors, be it tongue, soft palate or epiglottis; though slight sensitivity variations existed around the tongue, they were insignificant. These data dispelled the tongue map myth.

Taste cells and receptors are distributed not only in the oral cavity, but also in other parts of the alimentary tract. Those beyond the oral cavity do not provide a conscious sense of taste, but integrate physiologic responses to digestion. Umami receptors have been detected in the stomach and pancreas. On ingestion of umami foods, the former communicate with the brain via vagus nerve and facilitate digestion in the stomach. The latter function under the central command of brain and prepare for digestion in the small intestine.

In Nov 2005, Investigator Philippe Besnard and his team discovered fat specific CD36 lingual receptors in rodents. Since then, speculations regarding the occurrence of similar receptors in human beings gained importance. Ultimately in Dec 2011, findings of Scientist Pepino published in Journal of Lipid Research, showed that such receptors did indeed exist in human beings; genetic variations of CD36 receptors influenced an individual’s degree of sensitivity to fat perception; a better understanding of how the receptor worked in people could be a lead to curb obesity.

Thanks to research that has enabled a fresh look at the topic of taste. In a nutshell, newer perspectives are:

  1. There are 5 basic tastes. Umami is the latest addition;
  2. Receptors for different tastes are not restricted to specific areas of the tongue, but pervade its taste-sensitive surface.
  3. Lingual fat receptors, CD36 have been discovered in human beings; fat may perhaps be the 6th taste.

References:

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