THE FIFTH TASTE: UMAMI and TASTE BUD DISCOVERIES

For centuries it was believed that the tongue only perceived four basic tastes: sweet, sour, salty, bitter. That was until the early 1900s when Professor Kikunae Ikeda (right) of Tokyo Imperial University began thinking about the taste of food and realised there was a taste which was common to asparagus, tomatoes, cheese and meat but which is not one of the four well-known tastes.

In 1907 Professor Ikeda began his experiments to identify the source of this distinctive taste. He knew it was present in broth made from kombu (a type of seaweed) found in traditional Japanese cuisine sohe started by making a huge quantity of it from which he succeeded in extracting crystals of glutamic acid (or glutamate) – an amino acid which forms one of the building blocks of protein. This was the source of the new distinctive taste which he named ‘umami' in 1908.

Professor Ikeda found that 100gms of dried kombu contain about 1gm of glutamate; he decided to try and make a seasoning of it. He realised that, for this to work, the glutamate had to have some of the same physical characteristics which are found in sugar and salt - it had to be easily soluble in water but neither absorb humidity nor solidify.

Ikeda discovered monosodium glutamate combined these good storage properties with a strong umami or savoury taste. It turned out to be an ideal seasoning because monosodium glutamate has no smell or specific texture of its own so can be used in many different dishes, where it naturally enhances the original flavour of the food.

‘Plant Scents’ [American Scientist (Vol 92 No 6 Nov-Dec 2004 p.514).

More details in: Susan McLaughlin and Robert F. Margolskee,
‘The Sense of Taste’ [American Scientist (Vol 82, No.6 Nov-Dec 1994 p.538)].
See also: www.glutamate.org/media

TASTE BUDS

[Left]: Human taste buds (SEM at 2,800X). This tongue is covered not by protruding papillae, but by soft, overlapping sheetlike cells, each with its own intricate surface pattern which is doubtless as distinctive as a fingerprint. (Source: Cornell University)

'The word ‘umami' is now widely recognized and used amongst chefs, food writers and food fans around the world, but not so long ago it was known only in Japan, or among scientists, and even then viewed with considerable skepticism. One man who has been aware of umami longer and understands it better than most is Professor Tim Jacob, School of Biosciences, University of Cardiff who specializes in the relationship between smell and taste.

“Umami has only been accepted in the west for the past 10 years or so, and the discovery of taste receptors for umami gave it credibility,” says Jacob.

'The taste receptors he’s talking about are the L-glutamate taste receptor (mGluR4), discovered in 1996 by Chaudhari et al. and two amino acid receptors, called T1R1 and T1R3, which were first reported in 2002 by Nelson et al. It was the discovery of these receptors on the tongue, which respond specifically to substances that contain the umami taste, that led to umami being taken seriously by scientists, chefs and those with an interest in food, and it being recognized as one of the basic tastes alongside sweet, salty, sour and bitter.

'Another area for further study that relates to this is the position of taste buds and receptors in the mouth. Many people may be familiar with diagrams of the human tongue, neatly divided into areas that respond to different basic tastes, such as the sweet area, and the bitter area.

'Although it was thought for many years that this was how the taste buds worked, this theory was subsequently disproved, partly due to the emergence of umami, and scientists began to agree that all tastes could be experienced all over the tongue. But again, Jacob suggests that this is not the whole story either. In fact, “certain regions are more sensitive to one or two tastes [so] it’s a case of throwing the baby out with the bathwater, to throw out the idea that there are sensors [for certain tastes] in certain areas.”

In fact, taste buds are not simply located on the tongue, but also on the palate, esophagus and throughout the oral cavity. Jacob is particularly keen to point out that there is a high density of umami taste buds on the palate in addition to those on the tongue, and what is more, these are connected to the brain by the facial nerve, which is separate to the nerves serving the tongue. Thus, he says, “umami has its own direct link to the brain.”

Jacob, however, gives a more fundamental explanation of the importance of umami as a taste, which touches on the basic role of taste in the way we eat. “The purpose of taste,” he says, “is to drive appetite … umami is the taste of proteins and amino acids, so it makes perfect sense that we have to have the umami taste.”

Source: Umami Information Center

[Left]: Tongue with bitter, sweet and umami receptors in green and sour receptors in red. Credit: Nicholas Ryba, NIDCR and Charles Zuker, UCSD

August 23, 2006

UCSD-led Team Discovers How We Detect Sour Taste

By Sherry Seethaler

A team headed by biologists from the University of California, San Diego has discovered the cells and the protein that enable us to detect sour, one of the five basic tastes.

The study reports that each of the five basic tastes is detected by distinct taste receptors—proteins that detect taste molecules—in distinct cells. The team previously discovered the sweet, bitter and umami (savory) receptors and showed that they are found in separate cells, but some researchers have argued that sour and salty tastes, which depend on the detection of ions, would not be wired in the same way.

“Our results show that each of the five basic taste qualities is exquisitely segregated into different taste cells” explained Charles Zuker, a professor of biology at UCSD and a Howard Hughes Medical Institute Investigator, who headed the study. “Taken together, our work has also shown that all taste qualities are found in all areas of the tongue, in contrast with the popular view that different tastes map to different areas of the tongue.”

Source:
UCSD/Department of Biological Sciences