Basic taste
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There is scientific dispute as to whether basic tastes exist per se or are simply an overly reductionist concept. There is also philosophical dispute between biochemists, who believe evidence for a chemical reaction in tongue tissue means there is a basic taste, and psychologists, who see taste as much more based on psychological states and experiences.
Psychologists speak more about "flavor profiles" than tastes, based on the ways people report experiencing taste. Such reports and testing tend to show even the classic four basic tastes shading into each other on a spectrum of experience.
Ancient history
In Western culture, the concept of basic tastes can be traced back at least to Aristotle, who cited "sweet" and "bitter," with "succulent," "salt," "pungent," "harsh," "astringent" and "acid" as elaborations of those two basics. The ancient Chinese Five Elements philosophy lists slightly different five basic tastes: bitter, salty, sour, sweet, and hot.Historically, the science of how humans sense taste has been full of misunderstandings and conflicting claims. The concept of basic tastes is probably too simplistic and does not account for more complex reactions sometimes described as "mouthfeel," or for tastes such as metallic that are generally not considered food-oriented. The major problem is confusion between the concept of taste, which generally refers to stimuli directly affecting the tongue, and flavor, which involves olfaction as well. Many obvious sensations, such at hot and astringent are still recognized by science, but considered "chemical senses" — mere pain reactions — rather than tastes. Whether that is a meaningful distinction is in dispute.
For many years, books on the physiology of human taste contained diagrams of the tongue showing levels of sensitivity to different tastes in different regions. There is some scientific foundation for these "maps", but they tend to oversimplify certain aspects of taste sensation.
Recent discoveries
In recent years, advances in chemistry and food research have led to suggestions of additional basic food flavors. The most well-known and generally accepted is the concept of a "fifth basic taste" called umami. Umami is generally described as the taste of the common food flavoring monosodium glutamate, or MSG, first isolated by Dr. Kikunae Ikeda at the Imperial University of Tokyo, Japan, in 1907. Recently it has been discovered that the umami taste is produced by interaction of NMDA and mGluR4 receptors [link].In November 2005, [it was reported] that a team of French researchers experimenting on rodents claimed to have evidence for a sixth taste, for fatty substances. 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.
Some Japanese researchers refer to a flavor called kokumi which has been described variously as continuity, "mouthfulness", and thickness.
Main five basic tastes
Saltiness
Saltiness is 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.Sourness
Sourness 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
Sweetness is produced by the presence of sugars, some proteins and a few other substances. 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. And yet sour still has a sweet taste to some. See also: Miraculin and Curculin.
| Molecule | Threshold |
|---|---|
| Sucrose | 10 |
| Lactose | 30 |
| 5-Nitro-2-propoxyaniline | 0.002 |
Bitterness
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 to enable people to avoid accidental poisoning.The bitterest substance known is the synthetic chemical denatonium, marketed as the trademarked Bitrex [link], 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.
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.
Umami
Savouriness or umami is the name for the taste sensation produced by the free glutamates commonly found in fermented and aged foods. The name comes from umami (旨味 or うまみ), the Japanese name for the taste sensation. The characters literally mean "delicious flavour." The same taste is referred to as xiānwèi (鮮味 or 鲜味) in Chinese cooking. In English, the name of the taste is sometimes spelled umame, but umami (which conforms to a more common romanization standard of Japanese) is much more common, as in [Society for Research on Umami Taste]. Umami is considered a fundamental taste in Japanese and Chinese cooking, but is not discussed as much in Western cuisine. In English, it is sometimes referred to as "savoury" (US: "savory", not to be confused with the herb known as savory), "meaty" or "moreish."Examples of food containing these free glutamates (and thus strong in the umami 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 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. Since not every glutamate produces an umami-like taste sensation, there is continuing investigation into the exact mechanism of how the umami taste is produced.
The additive monosodium glutamate, which was developed as a food additive in 1907 by Kikunae Ikeda, produces a strong umami taste. Umami 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 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.
Other sensations
The tongue can also feel other sensations, not generally called tastes per se or included in the five human tastes. These are largely detected by the somatosensory system.Temperature
Temperature is an essential element of human taste experience. Food and drink which — within a given culture — is considered to be properly served hot is often considered distasteful if cold, and vice versa.Humans also eat substances which cause false sensations of heat or cold:
Spiciness or (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, and Szechuan cuisine.
The two main plants providing this sensation are chili peppers (those fruits of the Capsicum plant that contain capsaicin) and black pepper.
Due to a lack of a specific word for this flavour ("hot" properly refers to temperature; "spicy", to any spice) in English, the French term piquant is occasionally used. Indeed, many languages have a specific term, e.g. Spanish picante, Dutch pikant, Finnish tulinen and Chinese 辣 là.
(False) 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.Astringency
Some food (tea, unripe fruits) contains 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: "hard", "styptic", "rough", "harsh" (especially for wine), "tart" (normally refers to sourness).
Fat
Recent research has revealed a potential taste receptor called the CD36 receptor to be reacting to fat, more specifically, fatty acids. [link] This receptor was found in mice, but probably exists among other mammals as well. In experiments, mouse individuals with a genetic defect not having the receptor didn't show an unusual urge to consume fatty acids that mice sharing it did. Mice missing the receptor also failed to prepare gastric juices in their digestive tracts to digest fat. This discovery may lead to a better understanding of the biochemical reasons behind this behavior, although more research is still necessary to confirm the relationship of CD36 and the cravings of fat.Tingly numbness
Chinese cooking includes the idea of 麻 má, the sensation of tingling numbness caused by spices such as Sichuan pepper. The cuisine of Sichuan province often combines this with chilli to produce a 麻辣 málà, "numbing-and-hot", flavour. [link]References
- Kikunae Ikeda. (1909). [New Seasonings]
- Bernd Lindemann, Yoko Ogiwara, and Yuzo Ninomiya. (2002). [The Discovery of Umami]
- Dunlop, Fuchsia. 'It's all a matter of taste', Financial Times (Europe: August 6 2005) p.W9
External links
- [Nature Neuroscience - Umami taste receptor identified]
- [Receptor and Transduction Processes for Umami Taste]
- [Researchers Define Molecular Basis of Human "Sweet Tooth" and Umami Taste]
| Sensory system - Gustatory system - [http://encycl.opentopia.com/ edit] |
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| Tongue > Taste bud | Gustatory cortex | Basic tastes |
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