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Umami the Fifth Basic Taste: History of Studies on Receptor Mechanisms and Role as a Food Flavor

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Three umami substances (glutamate, 5'-inosinate, and 5'-guanylate) were found by Japanese scientists, but umami has not been recognized in Europe and America for a long time. In the late 1900s, umami was internationally recognized as the fifth basic taste based on psychophysical, electrophysiological, and biochemical studies. Three umami receptors (T1R1 + T1R3, mGluR4, and mGluR1) were identified. There is a synergism between glutamate and the 5'-nucleotides. Among the above receptors, only T1R1 + T1R3 receptor exhibits the synergism. In rats, the response to a mixture of glutamate and 5'-inosinate is about 1.7 times larger than that to glutamate alone. In human, the response to the mixture is about 8 times larger than that to glutamate alone. Since glutamate and 5'-inosinate are contained in various foods, we taste umami induced by the synergism in daily eating. Hence umami taste induced by the synergism is a main umami taste in human.
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Review Article
Umami the Fifth Basic Taste: History of Studies on
Receptor Mechanisms and Role as a Food Flavor
Kenzo Kurihara
Aomori University, Aomori 030-0943, Japan
Correspondence should be addressed to Kenzo Kurihara; kurihara@aomori-u.ac.jp
Received  March ; Accepted  June 
Academic Editor: Francesco Perticone
Copyright ©  Kenzo Kurihara. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ree umami substances (glutamate, 󸀠-inosinate, and 󸀠-guanylate) were found by Japanese scientists, but umami has not been
recognized in Europe and America for a long time. In the late s, umami was internationally recognized as the h basic
taste based on psychophysical, electrophysiological, and biochemical studies. ree umami receptors (TR + TR, mGluR, and
mGluR) were identied. ere is a synergism between glutamate and the 󸀠-nucleotides. Among the above receptors, only TR
+ TR receptor exhibits the synergism. In rats, the response to a mixture of glutamate and 󸀠-inosinate is about . times larger
than that to glutamate alone. In human, the response to the mixture is about  times larger than that to glutamate alone. Since
glutamate and 󸀠-inosinate are contained in various foods, we taste umami induced by the synergism in daily eating. Hence umami
taste induced by the synergism is a main umami taste in human.
1. Introduction
In , the active principle of seaweed kombu was identied
as glutamate by Ikeda []. Taste of glutamate is uniquely
dierent from classical  basic tastes and he termed it umami
[]. 󸀠-Inosinate from dried bonito []and
󸀠-guanylate from
dried shiitake mushroom [] were also found to have umami
taste. Later umami substances have been found universally in
various foods. In human, there is a large synergism between
glutamate and 󸀠-inosinate or 󸀠-guanylate. However, since
umami substances alone have a rather weak umami taste,
umamitasteisnotacceptedinEuropeandAmericaforalong
time. Umami substances have been considered to be “avor
enhancer.”
Before the First International Symposium on Umami was
held in Hawaii, there were a number of problems in umami.
ere was no systematic psychophysical data on umami. In
electrophysiological studies, monosodium glutamate (MSG)
is usually used as an umami stimulus since glutamic acid
itself has no umami taste. Single taste bers which respond
to MSG always respond to NaCl and hence there is no
evidence indicating that there are single bers responding
only to umami stimuli. e synergism between glutamate
and 󸀠-nucleotides was seen in rodents, but magnitude of the
synergism was extremely lower than that in human.
Aer the International Symposium, the psychophysical
and electrophysiological studies showed that umami is inde-
pendent of the four classical basic tastes. In addition, dog
showedalargesynergismcomparabletothatinhuman.
Furthermore, mGluR, mGluR, and TR + TR were
identiedtobereceptorsforumamitaste.Basedonthese
studies, umami was internationally recognized as the h
basic taste.
Aboutg/dayofglutamatewhichcomesfromfree
glutamate in foods and digestion of proteins in foods is
adsorbed at small intestine. Most glutamate adsorbed is used
asmajoroxidativefuelforthegut,metabolizedintoother
nonessential amino acids and production of glutathione. at
is, dietary glutamate does not go to tissues such as brain and
muscle.
2. Discovery of Umami Substances
e seaweed kombu has been used as a material to make
dashi (soup stock) in Japan for a long time. In , Ikeda
Hindawi Publishing Corporation
BioMed Research International
Volume 2015, Article ID 189402, 10 pages
http://dx.doi.org/10.1155/2015/189402
BioMed Research International
Acidic pH
OOCCHCH2CH2COOH
NH3
+
(a)
Neutral pH
OOCCHCH2CH2COONa+
NH3
+
(b)
F : Structure of glutamic acid (a) and monosodium glutamate (b).
who was a professor of physical chemistry in University of
Tokyo began to identify the active principle in kombu and
identied the principle in the same year []. He used  kg
of dried kombu and extracted the principle with water [].
At acidic condition, he obtained crystals of glutamic acid
(Figure ),butglutamicaciditselfhassourtaste.Glutamic
acid has two carboxyl residues as shown in Figure .pKaof
𝛾-carboxyl residue is . and then this residue is COOat
neutral pH. Glutamic acid dissolved in water was neutralized
with NaOH and  g of crystals of monosodium glutamate
(MSG) was obtained. MSG has unique taste dierent from
classical  basic tastes (sweet, bitter, sour, and salty tastes).
He termed taste of MSG umami. Potassium glutamate and
calcium glutamate also have umami taste and then umami
taste is due to glutamate anion.
Dried bonito has been used to make dashi in Japan for a
long time. In , Kodama who was the best pupil of Ikeda
foundthattheactiveprincipleofdriedbonitois
󸀠-inosinate
(salt of 󸀠-inosinic acid) []. 󸀠-Inosinic acid is a nucleotide
and has phosphate residue. At neutral pH, 󸀠-inosinate is an
anion. Similar to glutamate, anion form of 󸀠-inosinic acid
has umami taste.
In , Kuninaka found that 󸀠-guanylate has umami
taste []. 󸀠-Guanylate is also a nucleotide which has phos-
phate residue. At neutral pH, 󸀠-guanylate is an anion. Later,
it was found that 󸀠-guanylate is an umami component in
shiitake mushroom.
3. Production and Decomposition of
Umami Substances
3.1. Glutamate. Free glutamate exists in various foodstus
as shown in Table  [].Proteinsarecomposedof
dierent amino acids. Most proteins contain glutamate in
high content. For example, glutamate contents of casein in
milk,gluteninwheat,glycinininsoybean,andmyosinin
muscle are –%. Although free glutamate has umami
taste, glutamate in proteins has no taste. Proteolysis during
fermentation produces free glutamate in high content.
Free glutamate is not easily broken by heating and then is
rather stable.
3.2. 5󸀠-Inosinate. 󸀠-Inosinate is produced by decomposition
of ATP (adenosine triphosphate). ATP is decomposed into
AMP which is further decomposed into 󸀠-inosinate. Produc-
tion of 󸀠-inosinate begins when animal is dead and slowly
proceeds. In the case of yellowtail, decomposition of ATP and
production of 󸀠-inosinate begin at the time of killing and the
concentration of 󸀠-inosinate reaches maximum level about
hoursaerkilling.ismeansthattheshisnotdelicious
just aer killing but becomes delicious about  hours aer
killing:
ATP 󳨀→ AMP 󳨀→ 5󸀠-Inosinate ()
󸀠-Inosinate is not easily broken by heating.
3.3. 5󸀠-Guanylate. 󸀠-Guanylate is produced by decomposi-
tion of ribonucleic acid. In living cells, ribonucleic acid does
not contact with ribonuclease and then the decomposition
does not occur. When cells are dead, cells are broken
and ribonuclease contacts with ribonucleic acid. en 󸀠-
guanylate is produced. Optimum temperature of the enzyme
is C. 󸀠-Guanylate is decomposed into guanosine by
nucleotidase. e optimum temperature of this enzyme is
C:
Ribonucleic acid 󳨀󳨀󳨀󳨀󳨀󳨀󳨀󳨀󳨀
ribonuclease 5󸀠-Guanylate 󳨀󳨀󳨀󳨀󳨀󳨀󳨀󳨀󳨀
nucleotidase Guanosine ()
󸀠-Guanylate as an umami substance was rst found in
dried shiitake mushroom. Content of 󸀠-guanylate in a raw
mushroom is rather low but is very high in dried mushroom.
In the process of drying, cells of mushroom are broken and
󸀠-guanylate is produced by decomposition of ribonucleic
acid by ribonuclease. Before cooking, the dried mushroom
is soaked in water. e water should be cold because 󸀠-
guanylate is decomposed into guanosine by nucleotidase at
room temperature. In cooking, temperature of the water con-
taining 󸀠-guanylate from the mushroom should be quickly
increased to Ctoproduce
󸀠-guanylate further.
4. Content of Umami Substances in
Various Foodstuffs
As described above, there are  umami substances, glutamate,
󸀠-inosinate, and 󸀠-guanylate. Contents of these substances
invariousfoodstushavebeenmeasured.econtentsvary
with state of preservation and aging and with measurement
method. e data shown in Table  are most reliable ones at
present [].
Glutamateiscontaineduniversallyinbothplantandani-
mal foodstus. Kombu and seaweed nori contain glutamate in
very high content. Among vegetables, tomato and tamarillo,
which is relative to tomato, contain glutamate in most high
contents. Animal foodstus also contain glutamate, but the
contents are relatively lower than those in plant foodstus.
Fermentedfoodscontainhighcontentofglutamatebrought
about by hydrolysis of proteins during fermentation. 󸀠-
Inosinate is contained only in animal foodstus. Particularly,
dried foodstus such as dried sardine and bonito contain 󸀠-
inosinate in high content. 󸀠-Guanylate is contained mainly
in mushrooms.
BioMed Research International
T : Contents of umami substances in various foodstus [].
Glutamate (mg/ g)
Plant Animal Traditional foods
Kombu – Scallop  Anchovies –
Nori (seaweed)  Kuruma shrimp  Cheese –
Tamarillo– Sea urchin  Fish sauce –
Tomato – Short necked clam  Soy sauce –
Macambo∗∗  Crab – Green tea –
Garlic  Egg yolk  Aged cured ham 
Potato –
Chinese cabbage –
Carrot –
Onion –
󸀠-Inosinate (mg/ g) 󸀠-Guanylate (mg/ g)
Dried bonito – Dried shiitake 
Dried sardine – Enoki (cooked) 
Yellowtail – Dried morel 
Sardine  Dried porcini 
Sea bream –
Tuna 
Chicken 
Pork 
Beef 
Relative to cacao plant.
∗∗Relative to tomato.
5. Synergism between Glutamate
and the Nucleotides
Synergism between glutamate and 󸀠-nucleotides (󸀠-
inosinate and 󸀠-guanylate) was found by Kuninaka [].
Kuninaka rst tasted 󸀠-inosinateandfeltthatumamitaste
of 󸀠-inosinate is rather weak and then tasted glutamate. He
felt that umami taste of glutamate is much stronger than that
of 󸀠-inosinate. To conrm this fact, he tasted 󸀠-inosinate
again without rinsing his mouth. Surprisingly, he felt a very
strong umami taste. is was because 󸀠-inosinate was mixed
with glutamate remaining on the tongue. Such synergism
also occurs between glutamate and 󸀠-guanylate.
Figure  shows strength of umami taste against the ratio
of glutamate and 󸀠-inosinate []. Strength of umami taste of
glutamate alone is rather weak (le end of the graph). Increase
of ratio of 󸀠-inosinate brings about a very strong umami
taste. Strength of umami taste of 󸀠-inosinate alone (right end
of the graph) is rather weak. us umami taste induced by the
synergism is extremely strong and the synergism is essentially
important.
In rats, the synergism occurs between 󸀠-inosinate and
various amino acids including glutamate. e response of
chorda tympani nerve to glutamate and 󸀠-inosinate is
enhanced by about . times []. us the extent of the
synergism in rats is much smaller than that in human.
Empirically, the synergism has been used in the cooking
before Kuninakas nding. To make the best dashi (soup
stock) in Japan, the seaweed kombu containing glutamate
Strength of umami
0 20 40 60 80 100
Glutamate
(100%) Ratio of inosinate Inosinate
(100%)
F : Eects of addition of 󸀠-inosinate to glutamate on
strength of umami [].
and dried bonito containing 󸀠-inosinateareusedtogether.
First kombu is soaked in water at C for one hour. Figure 
shows amino acid composition of kombu dashi obtained.
Surprisingly, the kombu dashi contains only glutamate and
aspartate []. Aspartate is also an umami substance, although
its umami taste is much weaker than that of glutamate. us
the kombu dashi is a pure umami solution. Mother milk
contained high content of glutamate []. e concentration
BioMed Research International
Asp
0.0
5.0
10.0
15.0
20.0
25.0
30.0
r
Ser
Asn
Glu
Gln
Pro
Gly
Ala
Val
Cys
Met
Ile
Leu
Tyr
Phe
Trp
Lys
His
Arg
Ino
(mg/100 mL)
F : Amino acid composition of kombu dashi [].
of glutamate in mother milk is of similar level to that of the
kombu dashi.
Secondly aks of dried bonito are added to the kombu
dashi andtheaksareeliminatedsoonaerboiled.edashi
obtained contains 󸀠-inosinate and histidine in addition to
glutamate and aspartate from kombu.isdashi has strong
umami taste due to synergism between glutamate and 󸀠-
inosinate. It is noted that mother milk contains 󸀠-inosinate
as well as glutamate and hence synergism between glutamate
and 󸀠-inosinate works in the milk.
Kombu and dried bonito are not easily available in
countries other than Japan. In this case, tomato or dried
one instead of kombu and the mushrooms containing 󸀠-
guanylate such as dried porcini and morel instead of dried
bonito can be used.
e synergism has been used in cooking in all over the
world. In China, chicken which contains 󸀠-inosinate and
vegetables containing glutamate such as spring onion and
ginger are cooked together. In Europe and America, beef
which contains 󸀠-inosinate is used together with vegetables
containing glutamate such as onion, carrot, celery, or tomato.
Glutamate and 󸀠-inosinate are commercially available
and hence a mixture of glutamate and 󸀠-inosinate produces
a strong umami taste, which is similar to the umami taste
brought about by combination of natural foods. Safety of
glutamate was conrmed as described later.
6. The Umami, Amino Acid, and Sodium
Chloride Interplay
Fuke and Konosu [] determined essential components of
snow crab meat taste by the omission test. First chemical
compositions of the boiled crab meat were analyzed. A
mixture of pure chemicals of the crab meat components
has a taste similar to crab meat taste. Omission of some
components still elicits crab meat taste, but that of some
components does not elicit crab meat taste anymore. us
essential components of crab meat taste were determined.
As shown in Ta b l e  [], three amino acids (glycine,
alanine, and arginine), two umami substances (glutamate
and 󸀠-inosinate), and two salts (NaCl and K2HPO4)are
essential components for the crab meat taste. According to
T : Essential components for crab meat taste [].
Component Concentration
(mg/ mL) Role of component
Glycine  Characterization of taste of
crab meat
Alanine 
Arginine 
Glutamate  Addition of umami
󸀠-Inosinate 
NaCl 
Enhancement of tastes of
amino acids and umami
substances
KHPO
our experience, K2HPO4does not so contribute to crab meat
taste.
Essential components of many other foods are also amino
acids, umami substances, and salts. For example, a scallop is a
sweet shellsh because it contains sweet amino acid, glycine
in very high content (, mg/ g) together with alanine
and arginine. Sea urchin eggs have unique taste which is
due to methionine. us species and content of amino acids
contribute to characteristic taste of foods.
Elimination of the umami substances from the essential
components of the crab meat taste leads to loss of delicious
taste of the crab meat. Umami substances give deliciousness
to foods.
Elimination of NaCl from the components of crab meat
tastebringsaboutaveryweaktaste.atis,NaClhasan
essential component to enhance tastes of other components.
In order to clarify the enhancing eect of NaCl, the
eect of NaCl on sweet taste of glycine was examined
psychophysically []. e results show that sweet taste of
glycine is greatly enhanced by the presence of NaCl. To
conrm the enhancement of NaCl more quantitatively, the
recording of canine chorda tympani nerve (taste nerve) was
carried out []. Figure  shows that the response to glycine is
greatly enhanced by adding of NaCl. Maximum enhancing
eect is seen at mM (.%) NaCl. One hundred mM
NaCl itself has only weak saltiness. Further increase of NaCl
concentration decreases the enhancement. e enhancement
byNaClwasalsoseenwithotheraminoacids.
e responses to umami substances such as glutamate,
󸀠-inosinate, and 󸀠-guanylate were also enhanced by NaCl
[]. Figure  shows the enhancing eect of NaCl on the
response to glutamate. Maximum enhancing eect is also
seen at  mM NaCl. us NaCl of rather low concentration
is essentially important for tastes of foods.
First role of the umami substances is to give umami
taste itself. As mentioned in Section ,kombu dashi is a pure
umami solution. Komb dashi and the dashi made from kombu
anddriedbonitohaveapureumamitaste.Secondroleof
the umami substances is to give deliciousness to foods. For
example, elimination of the umami substances from essential
components for crab meat taste lost deliciousness of crab
meat taste.
BioMed Research International
Log NaCl concentration (M)
Relative response
−4 −3 −2 −1 0
0
1
2
3
4
F : Canine taste nerve response to  mM glycine as a
function of NaCl concentration [].
Relative response
−3 −2 −1
0
0
0.5
0.25
0
Log NaCl concentration (M)
F : Canine taste nerve response to  mM glutamate as a
function of NaCl concentration [].
Rolls []showedthatodortogetherwithglutamate
brings about pleasantness in primates. When glutamate is
given in combination with a consonant, savory odor (veg-
etable), the resulting avor, formed by a convergence of the
taste and olfactory pathways in the orbitofrontal cortex, can
be much more pleasant.
ere are kokumi taste substances which themselves have
no taste but an ability to enhance umami, sweet, and salty
tastes []. Various extracellular calcium-sensing receptor
agonists 𝛾-glutamyl peptides such as 𝛾-Glu-Cys-Gly and 𝛾-
Glu-Val-Gly are kokumi taste substances. Since these kokumi
taste substances are contained in foods, the substances
contribute to taste of foods.
7. Umami Was Recognized as
the Fifth Basic Taste
All umami substances were found by Japanese scientists and
henceumamitastehasbeenwellacceptedbytheJapanese.
However in Europe and America, umami taste has not been
accepted fora long time. Glutamate itself has been considered
to have no taste and the ability to enhance food avors. en
glutamate has been called “avor enhancer.” In these times,
no original paper on umami taste has been accepted in any
journal published in America and Europe.
In , Japanese scientists who have studied on umami
established “Umami Research Organization.” is organiza-
tion held international umami symposiums in Hawaii [],
Sicily [], Bergamo [], and Tokyo []. In addition, the
umami section was provided in International Symposium on
Olfaction and Taste (ISOT) from th ISOT () held in
Sapporo.
In Hawaii, Yamaguchi [] reported psychophysical data
on umami taste. She examined similarities among  taste
stimuli and showed that the four basic tastes (sweet, sour,
salty,andbitter)arelocatedatthefourverticesofathree-
dimensional tetrahedron and umami is located clearly apart
from any vertices of the tetrahedron. is implies that umami
taste is dierent from the four basic tastes. It was conrmed
that umami has no ability to enhance any basic tastes.
Since glutamate has umami taste, monosodium glutamate
(MSG) is usually used as an umami stimulus in electrophysio-
logical studies. Application of MSG to tongue elicits impulses
in taste nerve bers. Single taste nerve bers which respond to
MSG always respond to NaCl and hence the response to MSG
has been considered to be due to Na+containedinMSG.en
it has been considered that there is no single ber specic to
umami substances.
Ninomiya and Funakoshi [] showed that there are
single bers in mice glossopharyngeal nerves which respond
toMSGbutrespondonlypoorlytoNaCl.BaylisandRolls
[]measuredresponsesofsinglenervebersinthemacaque
taste cortex and found single bers which responded best to
glutamate.
Synergism between glutamate and the 󸀠-nucleotides in
human is extremely large as shown in Figure .However,the
synergism of rat taste nerves [] is much smaller than that in
human. We found that canine chorda tympani nerves showed
a large synergism between glutamate and 󸀠-guanylate [].
Figure  shows the responses as a function of MSG concen-
tration in the absence and presence of . mM 󸀠-guanylate
(GMP). GMP (. mM) alone and a low concentration of
MSG alone do not elicit the response. But an increase of MSG
concentration induces a large response even at concentration
where MSG alone does not elicit the response. is large
synergism is similar to that in human.
In order to clarify whether the responses to umami
substances are due to Na+or not, amiloride which is an
inhibitor for NaCl response was added to a mixture of MSG
and 󸀠-GMP []. e large response brought about by the
synergism was not aected by amiloride (Figure ). is
implies that the responses to the umami substances are pure
umami responses.
In , umami section was provided in th ISOT held
in San Diego. In this section, many interesting data were
presented. e important topic was that a candidate for
umami receptor was proposed by Chaudhari and Roper,
which will be described in detail later.
Since the rst umami symposium, data indicating that
umamitasteisabasictastehavebeenaccumulated.econ-
ditions of a basic taste are as follows. () A basic taste should
not be produced by any combination of other basic tastes. ()
at a basic taste is independent of other basic tastes should
be proved by psychophysical and electrophysiological studies.
BioMed Research International
−0.2
−3 −2 −1
0
0
0.2
0.4
0.6
0.8
1.0
1.2
Relative response
MSG
Log MSG concentration (M)
MSG +0.5mM GMP
F : Canine taste nerve response to monosodium glutamate
(MSG) in the absence and presence of . mM 󸀠-guanylate (GMP)
[].
0
0
0.2
0.4
0.6
0.8
1.0
1.2
Relative response
NaCl
−0.6 −0.5 −0.4 − 0.3
Log amiloride concentration (M)
Umami (GMP +MSG)
F : Canine taste nerve response to a mixture of  mM
monosodium glutamate (MSG) and . mM 󸀠-guanylate (GMP)
and  mM NaCl as a function of amiloride concentration [].
() Specic receptor for a basic taste should exist. () A basic
tasteshouldbefounduniversallyinmanyfoods.
Umami taste is not produced by combination of any
four basic tastes. It was shown that umami taste is inde-
pendent of the four basic tastes by psychophysical and
electrophysiological studies. e receptor specic for umami
was identied (see later). Umami substances are contained
universallyinmanyfoods.Basedonthesefacts,umamitaste
wasrecognizedasthehbasictaste.
e above results in the ISOT were announced by news-
papers in all over the world and then umami became popular
to ordinary people. Now the word of umami is appearing in
many international dictionaries.
ebasictasteshaveeachcharacteristicphysiological
role. Typical sweet substances are sugars, which supply
energy. Hence sweet taste is a signal of energy. Poisonous
substances have bitter taste in general and hence bitter taste
is a signal of poison. Putrid matter has sour taste. In addition,
nonripping fruits have sour taste. e seeds of mature fruits
arespreadthroughdroppingsofanimals.Seedsofnonripping
fruits cannot be germinated. To prevent nonripping fruits
from eating by animals, the fruits seem to have sour taste.
Foranimals,sourtasteisasignaltoprotecteatingputrid
foods and nonripping fruits. Salts are essential elements for
health and salty taste is a signal of minerals. Glutamate which
is a main umami substance is most abundantly contained
in proteins. Glutamate is a precursor of a protein and a
component of protein hydrolysate. en umami taste is a
signal of protein.
On the contrary from the classical basic tastes, umami
is not profound taste. Even high concentration of umami
substances does not bring a strong taste. Umami harmonizes
othertastesinfoodsandbringsaboutmildnessanddelicious-
ness.
8. Receptors of Umami
8.1. mGlu4. Glutamate is a neurotransmitter in brain. ere
are many dierent types of glutamate receptors including
inotropic and metabotropic receptors. Under an idea that
glutamate receptors in brain may be candidates for umami
receptors in taste buds, glutamate receptors in brain were
lookedforinratlingualtissue[]. A number of inotropic
receptors were expressed in the lingual tissue, but no recep-
tors were preferentially localized to taste buds. On the other
hand, mGluR which is a member of metabotropic receptors
was expressed in taste buds.
mGluR is a class C GPRs (G-protein coupled receptors)
and has a long extracellular N terminus. mGluR expressed
in taste buds was an unusual variant of mGluR []. at
is, taste-mGluR expressed in taste buds lacks % of the
receptor’s extracellular N terminus. us taste-mGluR is
truncated version of the mGlR in brain.
e concentration of glutamate to activate taste-mGluR
is approximately two orders of magnitude less sensitive to
glutamate than mGluR in brain whose concentration is
micromolar range. e concentration of glutamate to activate
umami taste is –mM in rodents and the concentration
of glutamate to activate taste-mGluR is similar to con-
centration to activate umami taste. On the other hand, the
synergism between glutamate and the 󸀠-nucleotides is not
seen in taste-mGluR.
Later mGluR which is a metabotropic glutamate receptor
wasalsofoundintastebuds[].
8.2. T1r1 + T1r3. Identication of olfactory receptors aected
studies on taste receptors. Buck and Axel []lookedfor
GPRs from the olfactory epithelium since cyclic AMP was
established to be a second messenger in olfactory system.
Similarly, GPRs from the tong epithelium were looked for.
First TRs were identied to be receptors for bitter stimuli
[] and a heterodimeric complex of TR + TR was
identied to be a receptor for sweet stimuli by a number of
groups (e.g., []).
Later TR + TR (Figure ) was identied to be an
amino acid receptor []. is receptor identied from
mice showed synergism between 󸀠-inosinate and not only
glutamate but also many other amino acids. is is consistent
with the recording of taste nerve responses in rat []and
BioMed Research International
T1R1
T1R3
Extracellular
region
Transmembrane
region
Cytoplasmic
region
Membrane
F : Schematic structure of TR + TR.
mice [], although in human, the synergism is seen between
󸀠-inosinate and only glutamate. Human TR + TR was
produced and this receptor showed the synergism between
󸀠-inosinate and only glutamate []. e behavior of this
receptor is consistent with psychophysical data in human and
then TR + TR was established to be umami receptor in
human.
TRs including TR and TR belong to family C of
GPCRs and have three regions: the large extracellular region,
the seven-spanning transmembrane region, and the cytoplas-
mic region []. e extracellular region is further divided
into the ligand-binding region, which is frequently called the
“Venus ytrap module,” and the cysteine-rich domain, which
intervenes between the ligand-binding and transmembrane
regions.
By site-directed mutagenesis and molecular modeling,
binding sites for glutamate and 󸀠-inosinate in human umami
receptor were claried to exist in Venus ytrap of TR
subunit []. Here glutamate binds close to the Venus ytrap
along the hinge-bending motion, which leads to stabilization
oftheactiveconformation.
󸀠-Inosinate binds to an adjacent
siteclosetothebindingsiteforglutamate.isleadsto
further stabilization of the active conformation. e structure
of TR is in dynamic equilibrium, where the ratio between
theclosed(active)andtheopen(inactive)conformationsis
modulated by the presence/absence of ligand [,]. us
the synergism is produced by an allosteric regulation.
8.3. Knockout Mice of T1R1 + T1R3 and mGluR4. Knockout
mice of TR and TR were produced and responses to
umami stimuli were examined by the measurements of
nerve and behavioral responses. Knockout of TR or TR
completely eliminated the response induced by synergism
between glutamate and 󸀠-inosinate []. e response to
glutamate alone was not examined.
Knockout mice of TRs were also carried out by other
groups. In this case, knockout of TR eliminated complete
loss of the responses induced by the synergism []. But the
response to glutamate alone was eliminated partly. at is, the
knockout mice still responded to glutamate alone. Similarly
knockout of TR eliminated the responses induced by the
synergism, but the response to glutamate alone was elimi-
nated partly []. e remaining response to glutamate alone
was reduced by addition of an antagonist of mGluR ((RS)--
aminoindan-,-dicarboxylic acid) or that of mGluR ((RS)-
𝛼-cyclopropyl--phosphonophenylglycine). At the highest
concentration of the antagonists, the response to  mM
glutamatewasreducedto%ofcontrolresponse.
ese results suggest that the receptors such as mGluR and
mGluR also contribute to umami reception.
Knockout mice of mGluR were also produced and
the responses to umami stimuli were recorded from taste
nerves []. e knockout mice showed signicantly smaller
responses to glutamate than wild-type mice. e residual
glutamate responses in the knockout mice were suppressed
by gurmarin (a TR blocker) and (RS)--aminoindan-,-
dicarboxylic acid (an antagonist for mGluR). ese results
provided functional evidences for the involvement in umami
taste responses in mice. It is noted that as of today there is no
report of the expression of mGluR and mGluR in human
fungiform papillae.
e degree of the synergism between glutamate and the
󸀠-ribonucleotides greatly varies with species of animals. In
dog, the synergism is much larger than that of rodents. As
shown in Figure , addition of 󸀠-guanylate to a low glutamate
of concentration which does not elicit the response induces a
large umami response. Similarly, the synergism is very large
in human as shown in Figure .Inhuman,umamitasteof
glutamate alone is rather weak, but addition of 󸀠-inosinate
increases umami taste severalfold. Umami taste induced by
the synergism is essentially important in human.
It was reported that some humans cannot taste glutamate
[]. Kim et al. []examinedvariationinthehumanTR
taste receptor genes and showed that there was variation
BioMed Research International
in genes TR, TR, and TR. Raliou et al. []found
variation of genes TR and TR in human fungiform
papillae and suggested that these receptor variants contribute
to interindividual dierences ofsensitivity to glutamate. us
TR + TR system mainly contributes to umami reception
in human.
8.4. Transduction Mechanism. ere are four types of taste
cells []. Among them, type II and type III taste cells are
able to transmit their signals to gustatory nerve bers. Type
III taste cells express synaptic vesicles, but type II cells do
not possess conventional synapses but have very close contact
with gustatory nerve bers.
Umami reception is performed in type II and type
III cells. Stimulation of umami receptor TR + TR by
umami stimuli activates G-protein and leads to activation of
phospholipase C𝛽(PLC𝛽) [,]. is activation pro-
duces inositol-,,-triphosphate (IP3)thatactivatesinositol-
,,-triphosphate receptor type  (IP3R) to induce Ca2+
release from the Ca2+ stores. e increase in [Ca2+]i activates
transient receptor potential of TRPM (transient receptor
potential cation channel subfamily M member ), leading to
the depolarization of the taste cell. Finally, the taste cell evokes
action potentials via voltage-gated Na+channels and releases
a transmitter to activate taste nerve bers. e transmitter
seems to be ATP []. It is also showed that glucagon-like
peptide- (GLP-) is secreted from taste buds by stimulation
with umami stimuli [].
Stimulation by umami stimuli of taste tissue brings about
a decrease of cyclic AMP level []. Meaning of the cyclic
AMP decrease is not elucidated.
9. Physiological Roles of Dietary Glutamate
and Its Metabolic Disposition
ere are glutamate receptors such as mGluR []and
TR + TR [] in stomach and intestinal epithelium. Stim-
ulation of glutamate receptors by luminal glutamate activates
vagal aerent nerve bers whose information is transmitted
toareasofbrains:themedialpreopticarea,thehypothala-
mic dorsomedial nucleus, and habenular nucleus []. is
stimulation seems to inuence physiological functions such
as thermoregulation and energy homeostasis.
e dietary glutamate including free glutamate and glu-
tamate produced by digestion of food proteins is about g
per day []. e glutamate is adsorbed at small intestine.
e adsorbed glutamate is extensively metabolized in rst
passbytheintestine.atis,mostglutamateisusedasa
major oxidative fuel for the gut and metabolized into other
nonessential amino acids. Glutamate is also an important
precursor for bioactive molecules such as glutathione.
Since most glutamate adsorbed at small intestine is used
as an oxidative fuel and metabolized into other amino acids,
almost glutamate does not enter into the hepatic portal vein
even when dietary glutamate is very high. Glutamate is a
nonessential amino acid and then glutamate is synthesized in
tissues such as muscle and brain. Glutamate is a neurotrans-
mitter in brain and then brain contains glutamate in high
content. Blood-brain barrier is impermeable to glutamate
even at high concentration [] and then dietary glutamate
is not needed for brain.
Inand,twotypesofstudiesonsafetyof
glutamate were reported. e rst report was a very short
letter on “Chinese restaurant syndrome” []. at is, eating
of Chinese foods causes numbness at the neck and arms and
palpitation, which is due to glutamate contained in the foods.
Although no statistical data are presented in the letter, the
news on the syndrome was spread all over the world. Later
a number of double-blind placebo-controlled studies were
conducted with the subjects who reported the syndrome and
it was concluded that there was no relation between glutamate
intake and the syndrome [].
Content of the second report was that injection of a
high concentration of glutamate into newborn mice induced
neuronal necrosis in several regions of brain []. How-
ever, to evaluate safety of food components by injection is
unreasonable because injection is quite dierent from oral
administration. For example, injection of KCl contained in
many foods such as an apple to animals leads to immediate
death. As mentioned above, mother milk contains high
concentration of glutamate and hence baby drinks a high
concentration of glutamate every day.
In , Joint FAO/WHO (Expert Committee on Food
Additives) determined that acceptable daily intake of gluta-
mate is not specied.
10. Discussion and Conclusion
e results obtained from rodents are not simply applicable
to human because there are large dierences between taste
system of rodents and that of human. () In human and
dog, sodium chloride largely enhances the responses to
amino acids, sugars, and umami substances, while such
enhancement is not seen in rodents (unpublished data). ()
In rodents, 󸀠-inosinate enhances the responses to various
amino acids, while 󸀠-inosinate enhances the response to only
glutamate in human and dog. () e synergism between
glutamate and the 󸀠-nucleotides is rather weak in rodents
but is extremely large in human and dog. () ere is a report
saying that, in mice, a mixture of glutamate and 󸀠-inosinate is
perceived as having a sweet or at least sucrose-like taste [].
Of course, it is unlikely in human.
As shown in the present paper, umami taste was shown to
be independent of the four basic tastes by psychophysical and
electrophysiological studies. e receptors specic for umami
were identied. Umami substances are found universally in
many foods. Based on these facts, umami was internationally
recognized as the h basic taste.
Dierent from the  basic tastes, umami does not exhibit
extensive taste even when the concentration of umami sub-
stances is largely increased. Umami substances are contained
universally in various foods. Umami taste harmonizes with
othertastesinfoodsandbringsaboutmildnessanddelicious-
ness.
mGluR, mGluR, and TR + TR were identied to
be receptors for umami. TR + TR exhibits a synergism
between glutamate and 󸀠-inosinate or 󸀠-guanylate, but
BioMed Research International
mGluR and mGluR do not exhibit the synergism. Similar
to dog, human exhibits an extreme large synergism although
glutamate and 󸀠-nucleotides alone exhibit only a small
umami taste. Since glutamate and 󸀠-inosinate are contained
in various foods, we taste umami induced by the synergism
between glutamate and 󸀠-inosinate in daily eating. Hence
TR + TR mainly contributes to umami taste in human.
A large amount of glutamate which comes from free
glutamate in foods and digestion of proteins in foods is
adsorbed at small intestine. Most glutamate adsorbed is used
as major oxidative fuel for the gut, metabolized into other
nonessential amino acids and production of glutathione.
Almost glutamate does not enter into the hepatic portal vein
even when dietary glutamate is very high. Safety of glutamate
was conrmed by Joint FAO/WHO (Expert Committee on
Food Additives).
Conflict of Interests
e author declares that there is no conict of interests
regarding the publication of this paper.
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... First discovered and coined by Ikeda (1909), umami, Japanese for "deliciousness" is the distinct savory taste of broths, but also of cooked meat, (shell)fish, tomatoes, mushrooms, and certain cheeses (Kurihara, 2015;Zhang et al., 2013). The first compound to be identified reported to elicit umami was glutamic acid (Ault, 2004;Ikeda, 1909). ...
... The number of members within each class is indicated between brackets. The taste receptor families TAS1R and GRM belong to the glutamate class whereas the TAS2R family belongs to the Frizzled & Taste 2 class The GRMs that mediate umami tasting are short versions of the glutamate neuroreceptors, missing large parts of the extracellular N-terminal domain (Kurihara, 2015;San Gabriel et al., 2005). Both GRM1 and GRM4 are expressed in taste buds but are about one hundred times less sensitive to glutamate than the brain-variants (Kurihara, 2015;San Gabriel et al., 2005). ...
... The taste receptor families TAS1R and GRM belong to the glutamate class whereas the TAS2R family belongs to the Frizzled & Taste 2 class The GRMs that mediate umami tasting are short versions of the glutamate neuroreceptors, missing large parts of the extracellular N-terminal domain (Kurihara, 2015;San Gabriel et al., 2005). Both GRM1 and GRM4 are expressed in taste buds but are about one hundred times less sensitive to glutamate than the brain-variants (Kurihara, 2015;San Gabriel et al., 2005). ...
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Understanding taste is key for optimizing the palatability of seaweeds and other non‐animal‐based foods rich in protein. The lingual papillae in the mouth hold taste buds with taste receptors for the five gustatory taste qualities. Each taste bud contains three distinct cell types, of which Type II cells carry various G protein‐coupled receptors that can detect sweet, bitter, or umami tastants, while type III cells detect sour, and likely salty stimuli. Upon ligand binding, receptor‐linked intracellular heterotrimeric G proteins initiate a cascade of downstream events which activate the afferent nerve fibers for taste perception in the brain. The taste of amino acids depends on the hydrophobicity, size, charge, isoelectric point, chirality of the alpha carbon, and the functional groups on their side chains. The principal umami ingredient monosodium l‐glutamate, broadly known as MSG, loses umami taste upon acetylation, esterification, or methylation, but is able to form flat configurations that bind well to the umami taste receptor. Ribonucleotides such as guanosine monophosphate and inosine monophosphate strongly enhance umami taste when l‐glutamate is present. Ribonucleotides bind to the outer section of the venus flytrap domain of the receptor dimer and stabilize the closed conformation. Concentrations of glutamate, aspartate, arginate, and other compounds in food products may enhance saltiness and overall flavor. Umami ingredients may help to reduce the consumption of salts and fats in the general population and increase food consumption in the elderly.
... Humans are able to perceive 4 basic types of taste sensations including the salty, sweet, sour and bitter, while some studies have reported about one more kind of taste "Umami." [12,13] Taste sensation is produced when a reaction occurs in between the taste receptors which are present within the taste buds and the food ingested. Taste buds are located not only on the tongue but also on the palate, uvula, epiglottis, pharynx and the upper parts of the esophagus. ...
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Context and aim: The major afflictions such as odynophagia (painful swallowing) and trismus that occur in patients with oral submucous fibrosis (OSMF) are well documented, but the impairment of gustatory functions has not received much consideration in the past. The present study was planned with a similar intent to assess and compare the alteration in taste perception among gutkha chewers with and without OSMF and healthy subjects. Materials and methods: The present study was designed as a prospective case-control study comprising 90 individuals within an age range of 15-50 years who were divided into three groups with Group A consisting of 30 patients who were gutkha chewers with OSMF, Group B consisting of 30 individuals who were gutkha chewers but without OSMF and Group C consisting of 30 healthy subjects who were included as normal controls. The taste intensity response scores for the four basic tastes were recorded and the results obtained were, then, subjected to statistical analysis. Statistical analysis used: The data were analyzed using SPSS version 16.0 (SPSS Inc., Chicago, IL, USA). Comparison of the said parameters was done using Chi-square test, analysis of variance and Tukey's post-hoc test. P < 0.05 was considered statistically significant. Results: The findings of the present study suggested that all taste sensations were affected more in Group A patients than the Group B and Group C individuals. Conclusion: The results obtained in the present study were found to be encouraging as it was demonstrated that taste perception varied significantly among the patients with OSMF as against those having habit of betel nut/gutkha chewing but those who did not develop OSMF and the normal healthy controls and this data, though, initial, might be used on a scientific basis to improve the quality of life in the affected patients as well as to prevent the further progression of the disease process.
... Ikeda later patented the production process and was the first to commercialize its monosodium salt (MSG) as a new seasoning 'Ajinomoto' in 1909 (Sano, 2009). The unique taste 'umami' after 100 years of its discovery was accepted as the fifth basic taste after the four classical tastes, sweet, sour, salty and bitter (Sanchez et al., 2018;Hermann, 2003;Ninomiya, 2015;Kurihara, 2015). MSG a potent flavor enhancer is a critical part of the taste of cheese, meat broths, seafood, and other food items (Sanchez et al., 2018). ...
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Ever since its discovery in 1957, Corynebacterium glutamicum has become a well-established industrial strain and is known for its massive capability of producing various amino acids (like L-lysine and L-glutamate) and other value-added chemicals. With the rising demand for these bio-based products, the revelation of the whole genome sequences of the wild type strains, and the astounding advancements made in the fields of metabolic engineering and systems biology, our perspective of C. glutamicum has been revolutionized and has expanded our understanding of its strain development. With these advancements, a new era for C. glutamicum supremacy in the field of industrial biotechnology began. This led to remarkable progress in the enhancement of tailor-made over-producing strains and further development of the substrate spectrum of the bacterium, to easily accessible, economical, and renewable resources. C. glutamicum has also been metabolically engineered and used in the degradation/assimilation of highly toxic and ubiquitous environmental contaminant, arsenic, present in water or soil. Here, we review the history, current knowledge, progress, achievements, and future trends relating to the versatile metabolic factory, C. glutamicum. This review paper is devoted to C. glutamicum which is one of the leading industrial microbes, and one of the most promising and versatile candidates to be developed. It can be used not only as a platform microorganism to produce different value-added chemicals and recombinant proteins, but also as a tool for bioremediation, allowing to enhance specific properties, for example in situ bioremediation.
... Taste peptides are oligopeptides with molecular weights lower than 3000 Da that have a special effect on taste or make a partial contribution to food flavor. Umami taste plays a crucial role in enhancing favorable flavors and pleasant tastes [2]. Therefore, umami peptides have received growing attention [3]. ...
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Umami peptides are naturally found in various foods and have been proven to be essential components contributing to food taste. Defatted peanut powder hydrolysate produced by a multiprotease (Flavorzyme, Alcalase, and Protamex) was found to elicit an umami taste and umami-enhancing effect. The taste profiles, hydrolysis efficiency, amino acids, molecular weight distribution, Fourier transform infrared spectroscopy (FT-IR), and separation fractions obtained by ultrafiltration were evaluated. The results showed that peanut protein was extensively hydrolyzed to give mainly (up to 96.84%) free amino acids and peptides with low molecular weights (<1000 Da). Furthermore, β-sheets were the major secondary structure. Fractions of 1–3000 Da and <1000 Da prominently contributed to the umami taste and umami enhancement. To obtain umami-enhancing peptides, these two fractions were further purified by gel filtration chromatography, followed by sensory evaluation. These peptides were identified as ADSYRLP, DPLKY, EAFRVL, EFHNR, and SDLYVR by ultra-performance liquid chromatography (UPLC), and had estimated thresholds of 0.107, 0.164, 0.134, 0.148, and 0.132 mmol/L, respectively. According to the results of this work, defatted peanut powder hydrolysate had an umami taste and umami-enhancing effect, and is a potential excellent umami peptide precursor material for the food industry.
... 18 Some of the foods with a high umami taste are kombu, the seaweed nori, aged cheese, dried shiitake mushroom, fermented products, fish sauce and soy sauce. 19 The global scientific community needed approximately one hundred years to accept umami as one of the basic tastes. 18 This study investigated gustatory function for all 5 tastes, including umami, and whether patients expressed any taste preference, which might help in improving their nutrition. ...
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Objective: Studies of taste perceptions in Parkinson's disease (PD) patients have been controversial, and none of these studies have assessed umami taste. This study aimed to assess umami, along with the other 4 taste functions in PD patients. Methods: Participants were tested for gustation using the modified filter paper disc method and olfaction using the modified Sniffin' Stick-16 (mSS-16) test (only 14 culturally suitable items were used). A questionnaire evaluated patients' subjective olfactory and gustatory dysfunction, taste preference, appetite, and food habits. Results: A total of 105 PD patients and 101 age- and sex-matched controls were included. The body mass index (BMI) of PD patients was lower than that of controls (PD = 22.62, controls = 23.86, p = 0.028). The mSS-16 score was 10.7 for controls and 6.4 for PD patients (p < 0.001) (normal ≥ 9). Taste recognition thresholds (RTs) for sweet, salty, sour, bitter and umami tastes were significantly higher in PD, indicating poorer gustation. All taste RTs correlated with each other, except for umami. Most patients were unaware of their dysfunction. Patients preferred sweet, salty and umami tastes more than the controls. Dysgeusia of different tastes in patients was differentially associated with poorer discrimination of tastes, an inability to identify the dish and adding extra seasoning to food. BMI and mSS-16 scores showed no correlation in either patients or controls. Conclusion: PD patients have dysgeusia for all five tastes, including umami, which affects their appetite and diet. Patients preferred sweet, salty and umami tastes. This information can help adjust patients' diets to improve their nutritional status.
Chapter
Improved understanding and ability to make consistently tender meat have made cooked flavor the determining factor in meat palatability. From the identification of umami flavor to dry-aging strategies, the development of meat flavor is very complex. Stemming from the presence of flavor precursors, and undergoing thermal degradation reactions to create volatile compounds responsible for the aroma and overall flavor of cooked meat. Investigations into precooking strategies, including livestock management and postharvest practices provide insight into development of flavor precursors, nonvolatiles, and muscle tissue as a baseline of what cooked meat flavor could become. Meat cookery methods can also promote flavor differences, including oxidation processes involved in deleterious flavor attributes such as warmed-over flavor. Additionally, evaluating flavor compounds is essential to connect cooked meat flavor to consumer acceptability. Investigating new, unique methods to quickly classify and quantify flavor compounds act as initial indicators of cooked meat quality, similar to marbling as a measure of palatability. Concurrently, sensory evaluation identifies relationships between flavor compounds and consumer flavor, a benchmark for depicting ideal flavor profiles across various cuts. Subtle changes in product composition and handling strategies could generate drastically different flavor results in cooked meat. As knowledge of flavor development increases, improved flavor outcomes should be possible.
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Background Sodium chloride intake far exceeds guidelines by health and regulatory agencies. Acknowledging the positive relationship between sodium intake and blood pressure, interest in substances which assist in sodium reduction while contributing a savory taste such as umami are highly investigated. Objective The objective of this scoping review was to identify and characterize studies investigating umami tastants on sodium reduction in food with the goal of informing future research. Methods A literature search was conducted in Medline, Embase, Cochrane Database, EBSCO PsycInfo, PROSPERO, NIH Reporter, Clinical Trials.gov and WHO Trials and completed in March 2022 to identify peer-reviewed publications among adults (≥ 18 years) with interventions focusing on umami tastants to reduce sodium content. Results The literature search identified 52 studies among which mono-sodium glutamate (MSG) was the most studied umami tastant or food. Further, the majority of research on umami was represented through cross-sectional sensory studies to determine acceptability of foods with part of the original sodium chloride replaced by umami tastants. Only one study investigated the use of an umami tastant on overall daily sodium intake. Conclusions To assist individuals in adhering to sodium reduction intake goals set forth by regulatory agencies and their guiding policies, these findings indicate that additional research on umami tastants including systematic reviews and prospective trials is warranted. In these prospective studies, both intermediate outcomes (dietary pattern changes, daily dietary intake of sodium, and blood pressure) and hard outcomes (incidence of hypertension or stroke as well as cardiovascular composite outcomes) should be considered.
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Umami is one of five basic tastes, the elucidation of its mechanism by the study of the interaction between umami polypeptides and hT1R1 umami receptors is of great significance. However, research on umami peptides targeting human T1R1 receptors is lacking, and the molecular mechanism remains elusive. Here, we successfully established a system to detect umami peptides targeting human T1R1 receptors by fluorescence spectroscopy, Surface Plasmon Resonance (SPR) and computational simulation. The sensory evaluation, calculated Kd value, and experimental affinity results between the four selected umami peptides (GRVSNCAA, KGDEESLA, KGGGGP, and TGDPEK) and glutamate were tested using this system, and all matched well. The maximum Ka value of GRVSNCAA was 479.55 M⁻¹, and the minimum affinity of TGDPEK was 2.67 M⁻¹. Computational simulations showed that the different peptide binding sites in the hT1R1 binding pocket occupied due to conformational changes are important factors for different taste thresholds, and that peptide hydrophobicity plays an important role in regulating affinity. Thus, our study enables rapid screening of high-intensity umami peptides and the development of T1R1 receptor-based umami detection sensors.
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Meat substitutes using alternative proteins can facilitate sustainable diets without compromising animal welfare. The fungal protein, also called mycoprotein is the biomass that results from the fermentation of a filamentous fungus. This paper reports the results of a consumer acceptance study of fungal protein-based meat substitutes using a mixed-method design with a web-based survey and a series of semi-structured interviews amongst European participants. Based on the description provided in the survey, 56% of participants were not directly familiar with fungal proteins but they understood its potential societal benefits. The overall Food Technology Neophobia Score (FTNS) of the sample was moderate (M = 40.0, range = 19–62), with more neophilic participants (52.9%) than neophobic (47.1%). FTN was a significant but weak predictor of Perceived Benefits (PB) and Purchase Intentions (PI). Younger participants perceived fungal proteins more positively, and city-dwellers had higher PI than rural dwellers. Reducetarians were more likely to purchase fungal proteins, compared to unrestricted omnivores. Participants with lower acceptance of fungal proteins’ association with mould had significantly lower PI than those who were comfortable with it. In turn, familiarity with fungal protein was positively associated with mould acceptance. The qualitative data suggested that the sensory attributes were the most important factor in the acceptance of meat substitutes. The participants also valued clean label products which were perceived as healthier. Familiarity with other products containing mold seemed to assuage concerns and drive acceptance of fungal protein. The findings suggest that the overall acceptance of fungal protein is still rather low. This may be attributed to the perceived low appeal and tastiness of available fungal protein products.
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A paper-based device (PAD) capable of colorimetric detection was developed to determine the presence of glutamate in various food samples. The PAD employs an enzymatic reaction with glutamate followed by an oxidation reaction with N-benzoyl leucomethylene blue (BLMB) in the presence of horseradish peroxidase. The designed PAD consists of a sample introduction zone connected to a channel that transports a sample solution to three detection zones. The detection zones contain pre-deposited reagents: glutamate oxidase, horseradish peroxidase, BLMB, a phosphate buffer, and poly(acrylic acid). The PAD is perpendicularly immersed into a sample solution and bent at a right angle using a 3D-printed holder to allow the sample to simultaneously flow into three different detection zones. When the PAD is immersed into a sample containing glutamate, glutamate oxidase produces hydrogen peroxide, which changes the pale blue color of BLMB to a deep blue color in the presence of horseradish peroxidase. Under the optimum conditions, the calibration curve between the logarithm of the glutamate concentrations and the color intensity was linear within a range of from 5×10⁻⁶ mol L⁻¹ to 10⁻² and with a correlation coefficient of 0.994. Using this system, the PAD successfully determined glutamate in soup stocks, sauces, snacks, and tomato juice without the need of complicated sample pretreatment. These results agreed with those of a commercially available glutamate assay kit, which was employed as a certification method (tstat = 1.95, tcrit = 2.57). The developed PAD is simple, easy to fabricate, portable, and could be used outside of equipped laboratories to determine the presence of glutamate in food samples.
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Previous electrophysiological investigation shows that combinations of compounds classified by humans as umami-tasting, such as glutamate salts and 5'-ribonucleotides, elicit synergistic responses in neurons throughout the rodent taste system and produce a pattern that resembles responses to sweet compounds. The current study tested the hypothesis that a synergistic mixture of monopotassium glutamate (MPG) and inositol monophosphate (IMP) possesses perceptual similarity to sucrose in mice. We estimated behavioral similarity among these tastants and the individual umami compounds using a series of conditioned taste aversion (CTA) tests, a procedure that measures whether a CTA formed to one stimulus generalizes to another. Our primary finding was that a CTA to a synergistic mixture of MPG + IMP generalizes to sucrose, and vice-versa. This indicates umami synergistic mixtures are perceived as having a sweet, or at least sucrose-like, taste to mice. Considering other recent studies, our data argue strongly in favor of multiple receptor mechanisms for umami detection, and complexity in taste perception models for rodents. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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Umami taste is elicited by L-glutamate and some other amino acids and is thought to be initiated by G-protein-coupled receptors. Proposed umami receptors include heterodimers of taste receptor type 1, members 1 and 3 (T1R1+T1R3), and metabotropic glutamate receptors 1 and 4 (mGluR1 and mGluR4). Accumulated evidences support the involvement of T1R1 + T1R3 in umami responses in mice. However, little is known about in vivo function of mGluRs in umami taste. Here, we examined taste responses of the chorda tympani (CT) and the glossopharyngeal (GL) nerves in wild-type mice and mice genetically lacking mGluR4 (mGluR4-KO). Our results indicated that compared to wild-type mice, mGluR4-KO mice showed significantly smaller gustatory nerve responses to glutamate and L(+)-2-amino-4-phosphonobutyrate (L-AP4, an agonist for group III mGluR) in both the CT and GL nerves without affecting responses to other taste stimuli. Residual glutamate responses in mGluR4-KO mice were not affected by (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG, an antagonist for group III mGluR), but were suppressed by gurmarin (a T1R3 blocker) in the CT and (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA, an antagonist for group I mGluR) in the CT and GL nerve. In wild-type mice, both quisqualic acid (an agonist for group I mGluR) and L-AP4 elicited gustatory nerve responses and these responses were suppressed by addition of AIDA and CPPG, respectively. Collectively, the present study provided functional evidences for the involvement of mGluR4 in umami taste responses in mice. The results also suggest that T1R1+T1R3 and mGluR1 are involved in umami taste responses in mice. Thus umami taste would be mediated by multiple receptors. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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Bitter taste perception provides animals with critical protection against ingestion of poisonous compounds. In the accompanying paper, we report the characterization of a large family of putative mammalian taste receptors (T2Rs). Here we use a heterologous expression system to show that specific T2Rs function as bitter taste receptors. A mouse T2R (mT2R-5) responds to the bitter tastant cycloheximide, and a human and a mouse receptor (hT2R-4 and mT2R-8) responded to denatonium and 6-n-propyl-2-thiouracil. Mice strains deficient in their ability to detect cycloheximide have amino acid substitutions in the mT2R-5 gene; these changes render the receptor significantly less responsive to cycloheximide. We also expressed mT2R-5 in insect cells and demonstrate specific tastant-dependent activation of gustducin, a G protein implicated in bitter signaling. Since a single taste receptor cell expresses a large repertoire of T2Rs, these findings provide a plausible explanation for the uniform bitter taste that is evoked by many structurally unrelated toxic compounds.
Article
In the oral cavity, taste receptor cells dedicate to detecting chemical compounds in foodstuffs and transmitting their signals to gustatory nerve fibers. Heretofore, five taste qualities (sweet, umami, bitter, salty and sour) are generally accepted as basic tastes. Each of these may have a specific role in the detection of nutritious and poisonous substances; sweet for carbohydrate sources of calories, umami for protein and amino acid contents, bitter for harmful compounds, salty for minerals and sour for ripeness of fruits and spoiled foods. Recent studies have revealed molecular mechanisms for reception and transduction of these five basic tastes. Sweet, umami and bitter tastes are mediated by G-protein coupled receptors (GPCRs) and second-messenger signaling cascades. Salty and sour tastes are mediated by channel-type receptors. In addition to five basic tastes, taste receptor cells may have the ability to detect fat taste, which is elicited by fatty acids, and calcium taste, which is elicited by calcium. Taste compounds eliciting either fat taste or calcium taste may be detected by specific GPCRs expressed in taste receptor cells. This review will focus on transduction mechanisms and cellular characteristics responsible for each of basic tastes, fat taste and calcium taste.