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Umami: The Taste of MSG

Dateline: 06/26/00

By Alan Bruzel

Some Primary Tastes

There are four historically recognized taste sensations, bitter, salty, sour, and sweet, which are recognized by the taste buds, chiefly located on the tip, sides, and back of the tongue. Each taste bud is an assembly of from 50 to 150 taste cells. Some taste cells in a single taste bud may respond to sweet molecules, others to salty molecules, still others to bitter molecules, etc. The classical representation of discrete areas of the tongue responding only to a specific taste (bitter, back of the tongue; salty, front; sour, sides; and sweet, tip) is therefore an overgeneralization.

In 1908, Kikunae Ikeda, intrigued by the flavor of seaweed broth, found that glutamic acid, an amino acid present in this concoction, was responsible for a flavor neither bitter, salty, sour, or sweet (nor for any combinations of these four), and argued that a fifth primary taste be recognized, which he named umami (pronounced oo-MOM-ee) meaning "delicious" or "savory." We know this flavor today as the taste of MSG, monosodium glutamate.

What Is Important about Umami?

Taste receptors (which are protein molecules) on the surfaces of taste cells respond to a particular primary taste: bitter, salty, sour, sweet, or umami. Identifying a taste receptor thus involves isolating the protein molecule responsible and demonstrating that the isolated molecule generates a signal (ultimately conveyed to the brain) in the presence of its specific taste molecule.

Working with taste receptors in rodents, Nirupa Chaudhari and Stephen Roper, both of the University of Miami, isolated a taste receptor, taste-mGluR4, and found that this receptor specifically responds to glutamic acid. This accomplishment (reported in February, 2000) makes taste-mGluR4 the first isolated taste receptor and, of course, the first isolated umami taste receptor. Interestingly, taste-mGluR4 is a smaller, truncated version of the brain glutamate receptor, mGluR4, which responds to the lower concentrations of glutamate found in the brain.

Why Taste Food At All?

There is an advantage to choosing potentially edible substances. Bitter tastes may alert the non-discriminating among us to reject untoothsome fare. Sweet tastes connote a high caloric morsel, and the umami taste response, with its ability to detect a commonly occurring amino acid, allows recognition of high protein content foods.

What the Web Has to Say about:
Umami: The Taste of MSG

Brain: Taste Triumph
Brief description of umami receptor first published in Nature Neuroscience. A Nature Science Update article by Sara Abdulla.

Fifth Taste, The
Science and the Citizen entry from Steve Mirsky, Scientific American.

Flavor: Keeping Pleasure in Its Place
Monosodium glutamate taste tests can fool food editors. From the International Food Information Council.

Lindemann, Bernd
Descriptions and criticisms regarding some mammalian tongue maps. From Saar University.

Neurosciences at Monell Chemical Senses Center
Overview of taste, smell, and other chemosensory mechanisms.

Roper, Stephen
Studies of chemical stimuli and taste receptors at the University of Miami School of Medicine.

Sense of Taste
Introduction to the molecular aspects of taste sensations. From John W. Kimball.

Sweet? Sour? Or Maybe Umami?
News report on glutamate taste receptor. From the Australian Broadcasting Corporation.

Taste Research Advances with Identification of Umami Receptor
News release describes taste bud research at the University of Miami.

Umami Taste Receptor Identified
Press release from Nature Neuroscience, where this work was first published.

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