The conventional wisdom, repeated in many textbooks, is that there are four primary tastes: salty, sour, sweet and bitter. Complex flavors are generally supposed to arise from a combination of these primary tastes, with the more subtle effects arising from olfaction.
There is a fifth taste, however, which is much less widely recognized. This is ‘umami’, better known in the west as monsodium glutamate (MSG). Umami was first identified as a taste in 1908 by Kikunae Ikeda of the Tokyo Imperial University. Ikeda, having been struck by the distinctive flavor of seaweed broth, isolated the molecule responsible for the flavor and showed that it was glutamate. Although taste researchers have known about Ikeda’s work for decades, it is only recently that umami has gradually gained wider public recognition, probably because of the increasing popularity of Asian food.
It makes good sense that animals should have evolved the ability to taste glutamate. As the most abundant amino acid, glutamate is present in many protein-containing foods, including meat, seafood and aged cheese. Glutamate is also used, in much smaller quantities, as a neurotransmitter in the brain, and neurons have a variety of receptors to detect its presence. In principle, these receptors could also be used to detect glutamate in food, and one of them (a protein called mGluR4) is known to be present in the taste buds of the tongue, making it a plausible candidate for the umami taste receptor. The problem with this idea, however, was that mGluR4 is very sensitive to glutamate, so if it were the taste receptor, one would predict that the tiniest trace of glutamate in food would give an overwhelming taste of umami, which clearly does not happen.
Now, a team of scientists from the University of Miami have solved the puzzle and identified the receptor for umami. The molecule they describe is a modified form of mGluR4, in which the end of the molecule is missing. The strong binding of glutamate to mGluR4 requires this terminal region, and so its absence explains why the truncated form of mGluR4 is less sensitive to glutamate. The authors confirm that the truncated molecule, which they call ‘taste-mGluR4’, has all the properties that one would predict of an umami receptor. Most importantly, they show that it responds to glutamate at the same concentrations at which glutamate can be tasted, and that chemicals that mimic the taste of glutamate also activate the receptor.
Now the hunt is on to find the receptors for sweet and bitter, which are still not known. Meanwhile, the identification of a receptor for umami is likely to strengthen its claim to recognition as a fifth primary taste, on an equal footing with the four that are better known.
Food Editors Prefer “Umami” Taste Sensation
Being a taste panelist is hard work. Not only does the job require a well-trained sense of smell and taste, it also means being able to accurately describe the collective experience of flavor perception.
One group particularly suited to this task, food editors, put their senses to work during an IFIC-sponsored workshop “Savor the Flavor in Food,” during the International Food Media Conference in Orlando.
Research in taste physiology has shown that there are many more tastes beyond the classic four of sweet, sour, salty and bitter, according to Susan Schiffman, Ph.D., professor of medical psychology and director of the weight loss clinic at Duke University Medical Center.
One taste sensation now gaining recognition among Western cultures is known as “UMAMI.” The UMAMI taste is conveyed by several substances naturally occurring in foods, including glutamate.
Food media conferees were challenged to identify the UMAMI taste provided by glutamate in one of three samples of chicken stock. The samples were all prepared from the same basic recipe using chicken parts and vegetables, varying only in the presence or absence of salt and monosodium glutamate (MSG). The editors ere not informed which samples contained which seasonings.
When asked to identify the broth that conveyed the UMAMI taste, 60 percent of the editors correctly identified the stock containing MSG.
In terms of taste preferences, however, 75 percent of the editors indicated they preferred the broth with the UMAMI flavor contributed by glutamate. They described the taste as “rich,” “well-rounded,” “savory,” “full-bodied,” “brothy,” and “more chicken-like.”
Although UMAMI was first identified by Oriental cooks 1200 years ago, it wasn’t until the turn of this century that scientists isolated glutamate and other substances which convey this distinctive flavor. Sensory research shows that glutamate does not enhance any of the four classic tastes, nor can the UMAMI taste be formed by any combination of the classic four.
Glutamate is an amino acid that is found throughout the human body. It’s also naturally present in protein-rich foods such as cheese, meat, fish and human milk. When present in its “free” form in foods — not bound together with other amino acids in protein-glutamate exerts its UMAMI-flavor effect.
MSG added to foods provides a similar flavoring function as the “free” glutamate that occurs naturally in foods. It is often used to flavor meats, poultry, seafood, soups, stews, sauces and gravies.
Thirty-eight percent of the editors mistakenly identified the salt-only chicken stock as the one containing MSG. Although many people have the misperception that MSG makes food taste saltier, MSG contains only one-third the amount of sodium as table salt. MSG can be used in many foods to reduce the total amount of sodium by 20 to 40 percent, while maintaining an acceptable flavor.
MSG is classified by the Food and Drug Administration as a Generally Recognized as Safe (GRAS) substance. All foods with added MSG must list the ingredient on the label as monosodium glutamate.
In conducting clinical research on persons with taste and smell impairments, Schiffman also has found that many consumers mistakenly believe MSG is a preservative or meat tenderizer.
“Having experienced the UMAMI taste sensation first-hand, hopefully food editors can help educate consumers about MSG’s unique and flavorful contribution to foods,” she said.
Savoriness or umami is the name for the taste sensation produced by the free glutamates commonly found in fermented and aged foods, for example parmesan and roquefort cheeses, as well as soy sauce and fish sauce. It is also found in significant amounts in various unfermented foods such as walnuts, grapes, broccoli, tomatoes, and mushrooms, and to a lesser degree in meat. The glutamate taste sensation is most intense in combination with sodium. This is one reason why tomatoes exhibit a stronger taste after adding salt. Sauces with umami and salty tastes are very popular for cooking, such as tomato sauces and ketchup for Western cuisines and soy sauce and fish sauce for East Asian and Southeast Asian cuisines.
The additive monosodium glutamate (MSG), which was developed as a food additive in 1907 by Kikunae Ikeda, produces a strong umami taste. Umami is also provided by the nucleotides IMP (disodium 5-inosine monophosphate) and GMP (disodium 5-guanosine monophosphate). These are naturally present in many protein-rich foods. IMP is present in high concentrations in many foods, including dried Bonito flakes (Used to make Dashi, a Japanese broth). GMP is present in high concentration in dried Shiitake mushrooms, used in much of Asian cooking. There is a synergistic effect between MSG, IMP and GMP which together in certain ratios produce a strong umami taste.
Umami is considered basic in Japanese and Chinese cooking, but is not discussed as much in Western cuisine, where it is sometimes referred to as “savory”, “meaty” or “moreish.”
The name comes from umami, the Japanese name for the taste sensation. The characters literally mean “delicious flavour.”
In English, the name of the taste is sometimes spelled umame, but umami (which conforms to the romanization standards of Japanese) is much more common, as in Society for Research on Umami Taste.
The same taste is referred to as xianwei in Chinese cooking.
A subset of umami taste buds responds specifically to glutamate in the same way that sweet ones respond to sugar. Glutamate binds to a variant of G protein coupled glutamate receptors.