Umami

For the record label, see Umami Records.

Ripe tomatoes are rich in umami components.

Umami (IPA: [uː mɑː mi]), popularly referred to as savoriness, is one of the five basic tastes together with sweet, sour, bitter, and salty. Umami is a loanword from the Japanese umami (うま味) meaning "pleasent savory taste". This particular writing was chosen by Professor Kikunae Ikeda from umai (うまい) "delicious" and mi (味) "taste". The Chinese characters 旨味 are used for a more general meaning, when a particular food is delicious.

Background

For a long time, scientists debated whether umami was indeed a basic taste; but in 1985 at the first Umami International Symposium in Hawaii, the term Umami was officially recognized as the scientific term to describe the taste of glutamates and nucleotides. Now it is widely accepted as the fifth basic taste. Umami represents the taste of the amino acid L-glutamate and 5’-ribonucleotides such as guanosine monophosphate (GMP) and inosine monophosphate (IMP). It is described as a pleasant "brothy" or "meaty" taste with a long lasting, mouthwatering and coating sensation over the tongue. This is due to the detection of the carboxylate anion of glutamate in specialized receptor cells present on the human and animal tongue. Its fundamental effect is the ability to balance taste and round the total flavor of a dish. Umami clearly enhances the palatability of a wide variety of foods (for review Beauchamp, 2009). Glutamate in acid form (Glutamic acid) imparts little umami taste; whereas the salts of glutamic acid, known as glutamates, can easily ionize and give the characteristic umami taste. GMP and IMP amplify the taste intensity of glutamate.

Discovery of umami taste

Kikunae Ikeda.

Glutamate has a long history in cooking. Fermented fish sauces (garum), rich in glutamate, were already used in ancient Rome. In the late 1800s, chef Auguste Escoffier, who opened what was the most glamorous, expensive, and revolutionary restaurant in Paris, created meals that tasted like no combination of salty, sour, sweet and bitter. He had not, however, known the chemical source for this unique quality. Umami was not properly identified until 1908 by the scientist Kikunae Ikeda, a Professor of the Tokyo Imperial University. He found that glutamate was responsible for the palatability of the broth from kombu seaweed. He noticed that the taste of kombu dashi was distinct from sweet, sour, bitter and salty and named it umami. Later, a disciple of professor Ikeda, Shintaro Kodama, discovered in 1913 that dried bonito flakes contained another umami substance . This was the ribonucleotide IMP. In 1957, Akira Kuninaka realized that the ribonucleotide GMP present in shiitake mushrooms also conferred the umami taste. One of Kuninaka's most important discoveries was the synergistic effect between ribonucleotides and glutamate. When foods rich in glutamate are combined with ingredients that have ribonucleotides, the resulting taste intensity is higher than the sum of both ingredients. This is why Japanese make dashi with kombu seaweed and dried bonito flakes, Chinese add Chinese leek and cabbage with chiken soup or Italians combine Parmesan cheese on tomato sauce with mushrooms. The umami taste sensation of those ingredients mixed together surpasses the taste of each one alone.

Properties of umami taste

Umami has a mild but lasting after taste difficult to describe. It induces salivation and a furriness sensation on the tongue, stimulating the throat, the roof and the back of the mouth (for review Yamaguchi, 1998). By itself, umami is not palatable, but it makes a great variety of foods pleasant especially in the presence of a matching aroma. But like other basic tastes, with the exception of sucrose, umami is pleasant only when used within in a relatively narrow concentration range. Moreover, the optimum umami taste depends on the amount of salt and, at the same time, low-salt foods can maintain a satisfactory taste with the appropriate amount of umami. In fact, Roinien et al. showed that ratings on pleasantness, taste intensity and ideal saltiness of low salt soups were greater when the soup contained umami, whereas low-salt soups without umami were less pleasant. Some population groups, such as the elderly, may benefit from umami taste because their taste and smell sensitivity is impaired by age and multiple medications. The loss of taste and smell can contribute to a poor nutritional status increasing their risk of disease.

Foods rich in umami

Many foods that we consume daily are rich in umami. A person's first encounter with umami is with breast milk. Breast milk contains roughly the same amount of umami as Japanese broths or bouillon, called dashi. Umami taste is common to foods that contain high levels of L-glutamate, IMP and GMP, most notably in fish, cured meats, vegetables (e.g. mushrooms, ripe tomatoes) or green tea, and fermented and aged products (e.g. cheeses, shrimp pastes, soy sauce, etc.).
Japanese dashi gives a very pure umami taste sensation because of its high content of L-glutamate from sea kombu (Laminaria japonica) and inosinate from dried bonito flakes (katsuobushi) or small dried sardines (niboshi). Western broths and bouillons give a more complex taste because of a wider mixture of amino acids from bones, meats and vegetables.

Taste receptors

Biochemical studies have identified the taste receptors responsible for the sense of umami, a modified form of mGluR4, mGluR1 and taste receptor type 1 (T1R1 + T1R3). The New York Academy of Sciences corroborated their acceptance stating that "Recent molecular biological studies have now identified strong candidates for umami receptors, including the heterodimer T1R1/T1R3, and truncated tye 1 and 4 metabotropic glutamate receptors missing most of the N-terminal extracellular domain (taste-mGluR4 and truncated-mGluR1) and brain-mGluR4 …The finding that human T1R1/T1R3 heterologously expressed in human embryonic kidney cells preferentially responds to glutamate, provides strong molecular evidence for specific umami detection in humans. However, these other receptors remain candidates and the role of each type of receptor in taste bud cells remains unclear."

Umami tastes are initiated by these specialized receptors, with subsequent steps involving secretion of neurotransmitters including serotonin. Other evidence indicates guanosine derivatives may interact with and boost the initial umami signal.

Cells responding to umami taste stimuli do not possess typical synapses, but instead secrete the neurotransmitter ATP in a mechanism exciting sensory fibers that convey taste signals to the brain.

In monkey studies, most umami signals from taste buds excite neurons in the orbitofrontal cortex of the brain, showing spatially specific characteristics:

• Single neurons having vigorous responses to sodium glutamate also respond to glutamic acid
• Some neurons display a mechanism of satiety.

The stomach can "taste" sodium glutamate using glumate receptors and this information is passed to the lateral hypothalamus and limbic system in the brain as a palatability signal through the vagus nerve.

References

• Flavor Chemistry: Thirty Years of Progress By Roy Teranishi, Emily L. Wick, Irwin Hornstein; Article: Umami and Food Palatability, by Shizuko Yamaguchi and Kumiko Ninomiya. ISBN 0-306-46199-4

• Barbot, Pascal; Matsuhisa, Nobu; and Mikuni, Kiyomi. Foreword by Heston Blumenthal. Dashi and Umami: The Heart of Japanese Cuisine. London: Eat-Japan / Cross Media, 2009

External links

• Umami Information Centre (NPO)
• International Glutamate Information Service
• Italian umami research
• Discovery of Umami
• Discovery of Umami Receptors
• Society for Research on Umami Taste
• "Who's umami? Human taste now comes in five flavours", CBC News, June 1, 2007
• "Sweet, Sour, Salty, Bitter… and Umami" NPR, November 1, 2007
• A New Taste Sensation, by Katy McLaughlin, Wall Street Journal, 12/8/07.
• Mouthfuls : huitlacoche is another beispiel, 24/7/08.