உமமிச் சுவை (இன்புளிச் சுவை)
N. Ganesan
இந்த உமமிச் சுவையை வரையறுத்து, அதற்கான ஏற்பான்கள் (receptors) மனிதனின் நாக்கில் இருப்பதை அறிவியல்The Discovery of Umami
+Author Affiliations
- Universität des Saarlandes, Medical Faculty, Physiology, Bldg 58, D- 66421 Homburg, Germany
- 1 Ajinomoto Co., Inc., European Head Office, 153, rue de Courcelles, 75817 Paris Cedex 17, France
- 2 Section Oral Function and Neurobiology, Department of Regulatory Oral Science, Kyushu University Graduate School, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka Prefecture, 812-8582 Japan
- Address correspondence to: Bernd Lindemann, Universität des Saarlandes, Medical Faculty, Physiology, Bldg 58, D- 66421 Homburg, Germany. e-mail: phb...@uniklinik-saarland.de
Sweet, bitter, salty and sour are the four taste qualities upon which the human sense of taste is based. But is this really all? Is there room for more basic tastes on the human tongue? Well, there is. Strangely, though, while people tasted it daily, the fifth taste long remained unknown and unnamed. Its final discovery, made nearly a century ago, was due entirely to a single man, a chemistry professor at the Imperial University of Tokyo, Kikunae Ikeda.
It was Ikeda's insight and endurance alone which powered this early work. The tedious chemical isolation and identification of the new taste substance was done without the help from postdoctorates or students, as would be usual today, aided only by one technician. The investigation was based on an observation concerning the dominant taste of dashi, a Japanese soup base. The taste of dashi is mild but, according to Ikeda, clearly distinct from that of the four basic tastes. Ikeda proceeded to isolate the principal taste substance from a main ingredient of dashi, the seaweed Laminaria japonica. This was done with the procedures of classical chemistry, aqueous extraction, removal of large-scale contaminants (mannitol, NaCl, KCl) by crystallization, lead precipitation and numerous other steps of preparative chemistry. Finally, low-pressure evaporation resulted in the slow crystallization of a single substance with the mass formula C5H9NO4: glutamic acid. Its taste was named umami, a word derived from the Japanese adjective umai (delicious). It has taken root as a scientific term internationally.
The scientific community received this discovery with moderate applause only. Many, especially in English-speaking countries, remained unconvinced. One hindrance for the acceptance may have been that the detailed publication of Ikeda's work appeared in Japanese (Ikeda, 1909). Other hindrances were that umami taste is mild even at high concentrations of the tastants. Furthermore, high concentrations of glutamate, an anion, are necessarily accompanied by cations, the salty or sour taste of which confused the issue. Umami research proceeded on a larger scale especially since about 1980. The umami substances L-glutamate, inosine 5′-monophosphate (IMP) and guanosine 5′-monophosphate (of which the latter two enhance the glutamate taste) were defined, and taste responses to them were investigated in humans and animals. Animal models, however, were of limited use as the responses of different species, even of different strains of mice, were at variance.
Today a search in PubMed (MedLine) for papers concerned with taste and containing the term `umami' retrieved 86 references. (For comparison, `sweet taste' retrieved 10 times more references published since 1980.) A search with the Google engine found >4000 web pages containing the phrase `umami'. Some of these pages were from restaurants advertising umami food. Others dealt with the misconception that glutamate contained in food might be harmful. But foremost among them were pages reprinting newspaper articles about the discovery of umami receptors.
The discovery of umami receptors, taste receptors for L-glutamate, using methods of molecular biology is one of the recent highlights of taste research. In 2000, a modified glutamate receptor of the brain was found, the taste-mGluR4. It is a G protein-coupled (metabotropic) receptor. The taste variety of mGluR4 has a truncated N-terminal to which L-glutamate still binds, albeit with reduced affinity. Presumably, therefore, the truncation adapted the receptor to the high glutamate concentration in food (Chaudhari et al., 2000). More recently, another umami receptor was discovered. Interestingly, this one is a heteromere built of the G protein-coupled receptors T1R1 and T1R3. In mice this heteromere responds to many amino acids contained in food, but in humans its response is preferentially to L-glutamate and is enhanced by IMP (Nelson et al., 2002). Shortly after Nelson et al.'s publication, these results were strongly confirmed by another group (Li et al., 2002). The sequencing and functional expression of a human taste receptor for glutamate determined by these studies provides a first molecular basis for Ikeda's pioneering work.
Humans consume high-calory food as fat, polysaccharides and proteins. All of these are tasteless but elicit taste sensations through cleavage products. Sweet taste is the taste of mono- and disaccharides, and guides us to the consumption of starch. Umami taste is elicited by the most common amino acid, L-glutamate, a cleavage product of all proteins. Such argues Ikeda in his article.
An English translation of Ikeda's paper `New seasonings' from 1909 is made available in this issue of Chemical Senses. We would like to thank the journal for this contribution to the history of our science. The publication of the translation, late though it may seem, is timely in view of the recent discovery of umami taste receptors.
- Oxford University Press
References
- ↵ Ikeda, K. (1909) New seasonings.J. Tokyo Chem. Soc. , 30,820 -836 [in Japanese].
- ↵ Chaudhari, N., Landin, A.M. and Roper, S.D. (2000) A novel metabotropic glutamate receptor functions as a taste receptor. Nat. Neurosci., 3,113 -119.
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- ↵ Li, X., Staszewski, L., Xu, H., Durick, K., Zoller, M. and Adler, E. (2002) Human receptors for sweet and umami taste. Proc. Natl Acad. Sci.
Escoffier, the legendary chef who in the 19th Century developed and updated traditional French cuisine, was perhaps the first person to identify umami. He created a dish comprising of a sort of veal gravy (jus) which proved to be exceptionally successful. Escoffier credited the success of the ingredient to a je ne sais quoi element that illusive fifth taste that has recently been identified as umami.
But what is umami?
Kikunae Ikeda, the father of Umami
In 1908 Kikunae Ikeda, chemist from Tokyo University, noticed a particular taste in asparagus, tomatoes,cheeses and meat and he proceeded to study the one element that contained an even stronger flavor of the same type, kombu (kelp). He eventually found out that all elements contained glutamate, an amino acid. He was the first one to identify this property and he then learned how to produce it in industrial quantities, patenting it as MSG, a flavor enhancer. That’s the word comes from Japanese and can be translated “pleasant savory taste”.
Many foods that may be consumed daily are rich in umami. Naturally occurring glutamate can be found in meats and vegetables, whereas inosinate comes primarily from meats and guanylate from vegetables. Thus, umami taste is common to foods that contain high levels of glutamate, IMP (Inosinic acid) – which professor Shintaro Kodama in 1913 connected to umami – and GMP (Guanosine monophosphate), linked to umami taste by Akira Kuninaka in 1957 – like fish, shellfish, cured meats, mushrooms, vegetables (tomatoes, spinach, celery), aged cheese, green tea and fermented product.
That is why umami has a history as old as Ancient Rome, where fermented anchovies sauce (garum) was widely appreciated. That explains why Parmesan cheese with tomato sauce with mushrooms is a match made in heaven.
Most humans first encounter with umami in breast milk.
Umami is so rooted in our gastronomic history that dialects of every Region in Italy use different definitions to describe it or to describe flavors that are not identified through the 4 canonic descriptions (salt, sweet, sour and bitter), as it would be impossible to translate into Italian.
Many chefs now fully recognize the power of umami – that keeps us coming back for more – like Massimo Bottura, owner of Osteria Francescana, fifth best restaurant in the world, who in 1995 served his dish “five ages of Parmigiano Reggiano” made with different textures and temperatures of Parmigiano Reggiano clearly referring to umami – or better, to five different levels of it.
Many chefs also discussed the controversial topic of MSG, often considered harmful: David Chang Chef of Momofuku restaurant discussed it thoroughly during MAD 2012, the food symposium organized by Rene Redzepi (video below), Noma’s Chef, the best restaurant in the world.