describe seven basic tastes: bitter, salty, sour, astringent, sweet, pungent
(eg chili), and umami. There are however five basic tastes that the tongue is
sensitive to: salt, sweet, bitter, sour, and umami, the taste of MSG. Umami is
a Japanese word meaning "savory" or "meaty" and thus applies to the sensation
of savoriness -- specifically, to the detection of glutamates, which are especially
common in meats, cheese and other protein-heavy foods. The action of umami receptors
explains why foods treated with monosodium glutamate often taste fuller or just
which has been quietly enjoyed by Eastern civilizations for years, was recently
brought to the forefront of western thought by the discovery by the University
of Miami of the actual receptors responsible for the sense of umami, a modified
form of mGluR4, in which the end of the molecule is missing. The researchers named
it 'taste-mGluR4'. The discovery of the receptor is interesting especially since
the receptor for bitter has not yet been identified.
five basic tastes
a taste produced by the presence of sodium chloride (and to a lesser degree other
salts). The ions of salt, especially sodium (Na+), can pass directly through ion
channels in the tongue, leading to an action potential.
is the taste that detects acids. The mechanism for detecting sour taste is similar
to that which detects salt taste. Hydrogen ion channels detect the concentration
of hydronium ions (H3O+ ions) that have dissociated from an acid. Hydrogen ions
are capable of permeating the amiloride-sensitive sodium channels, but this is
not the only mechanism involved in detecting the quality of sourness. Hydrogen
ions also inhibit the potassium channel, which normally functions to hyperpolarize
the cell. Thus, by a combination of direct intake of hydrogen ions (which itself
depolarizes the cell) and the inhibition of the hyperpolarizing channel, sourness
causes the taste cell to fire in this specific manner.
Sweetness is produced by the presence of sugars, some proteins and a few other
substances. Sweetness is often connected to aldehydes and ketones which contain
carbonyl group. Sweetness is detected by a variety of G protein coupled receptors
coupled to the G protein gustducin found on the taste buds. At least two different
variants of the "sweetness receptors" need to be activated for the brain to register
sweetness. The compounds which the brain senses as sweet are thus compounds that
can bind with varying bond strength to several different sweetness receptors.
The differences between the different sweetness receptors is mainly in the binding
site of the G protein coupled receptors. The average human detection threshold
for sucrose is 10 millimoles per litre. For lactose it is 30 millimoles per liter,
and 5-Nitro-2-propoxyaniline 0.002 millimoles per litre.
the taste which detects bases. Bitterness, like sweetness, is sensed by G protein
coupled receptors coupled to the G protein gustducin. Many people find bitter
tastes to be unpleasant; many alkaloids taste bitter, and evolutionary biologists
have suggested that a distaste for bitter things evolved because it enabled people
to avoid accidental poisoning. The bitterest substance known is the synthetic
chemical denatonium, marketed as the trademarked Bitrex , discovered in 1958.
Denatonium benzoate is a white, odourless solid used as an aversive agent, and
can be an additive that prevents accidental ingestion of a toxic substance by
humans, particularly children, and by animals. It is commonly used on denaturizing
ethanol. The synthetic substance phenylthiocarbamide (PTC) tastes very bitter
to most people, but is virtually tasteless to others; furthermore, among the tasters,
some are so-called "supertasters" to whom PTC is extremely bitter. This genetic
variation in the ability to taste a substance has been a source of great interest
to those who study genetics. In addition, it is of interest to those who study
evolution since PTC-tasting is associated with the ability to taste numerous natural
bitter compounds, a large number of which are known to be toxic. Quinine, the
anti-malarial prophylactic, is also known for its bitter taste and is found in
tonic water. Bitter taste receptors are known specifically as T2R's (taste receptors,
type 2). They are identified not only by their ability to taste for certain "bitter"
ligands, but also by the morphology of the receptor itself (surface bound, monomeric).
is the name for the taste sensation produced by the free glutamates commonly found
in fermented and aged foods. In English, it is sometimes described as "meaty"
or "savoury". In the Japanese, the term umami is used for this taste sensation,
whose characters literally mean "delicious flavour." Umami is now the commonly
used term by taste scientists. The same taste is referred to as xianwèi in Chinese
cooking. Savoury is considered a fundamental taste in Japanese and Chinese cooking,
but is not discussed as much in Western cuisine.
of food containing these free glutamates (and thus strong in the savoury taste)
are parmesan and roquefort cheese 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 savoury 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. Since not every glutamate produces a savoury-like taste sensation, there
is continuing investigation into the exact mechanism of how the savoury taste
sensation is produced.
additive monosodium glutamate (MSG), which was developed as a food additive in
1907 by Kikunae Ikeda, produces a strong savoury taste. Savoury is also provided
by the nucleotides disodium 5’-inosine monophosphate (IMP) and disodium 5’-guanosine
monophosphate (GMP). These are naturally present in many protein-rich foods. IMP
is present in high concentrations in many foods, including dried skipjack tuna
flakes used to make dashi, a Japanese broth. GMP is present in high concentration
in dried shiitake mushrooms, used in much of the cuisine of Asia. There is a synergistic
effect between MSG, IMP and GMP which together in certain ratios produce a strong
umami taste. A subset of savoury 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.
Taste? -- Fat
2005, it was reported that a team of French researchers experimenting
on rodents claimed to have evidence for a sixth taste, for fatty
substances. Investigator Philippe Besnard and his team believe
the CD36 receptors that they found on rodents, were important
for evolutionary reasons - to ensure animals ate a high energy
diet when foods were scarce. It is speculated that humans may
also have the same receptors. Fat has occasionally been raised
as a possible basic taste since at least the 1800s.
of 'Fat' Taste Could Hold the Key to Reducing Obesity --
now find that those with a high sensitivity to the taste of fat
consumed less fatty foods and had lower BMIs than those with lower
Temperature as an 'False Heat' or False Coolness'
Coolness -- Some substances activate cold trigeminal receptors. One can sense
a cool sensation (also known as "cold", "fresh" or "minty") from, e.g., spearmint,
menthol, ethanol or camphor, which is caused by the food activating the TRP-M8
ion channel on nerve cells that signal cold. The reactions behind this sense are
therefore analogous to those behind the hot sense. Unlike the actual change in
temperature described for sugar substitutes, coolness is only a perceived phenomena.
(false) heat --Substances such as ethanol and capsaicin cause a burning sensation
by inducing a trigeminal nerve reaction together with normal taste reception.
The heat is caused by the food activating a nerve cell ion channel called TRP-V1,
which is also activated by hot temperatures. The sensation, usually referred to
as "hot" or "spicy", is a notable feature of Mexican, Indian, Tex-Mex, Szechuan,
Korean, and Thai cuisine. The two main plants providing this sensation are chili
peppers (those fruits of the Capsicum plant that contain capsaicin) and black
such as tea or unripe fruits, contain tannins that constrict organic tissue. The
best example of this is unripe persimmons, whose juice causes a very unpleasant
astringent sensation on any part of the mouth it touches. Less exact terms for
the astringent sensation include: "rubbery", "hard", "styptic", "dry", "rough",
"harsh" (especially for wine) and "tart" (normally referring to sourness).
information on the Molecules of Taste
Bernd (2000). "A taste for umami". Nature Neuroscience
Huang A. L., et al.
Nature, 442. 934 - 938 (2006)
Ishimaru Y., et al. PNAS, 103. 12569 - 12574