Basic taste
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The basic tastes are the commonly recognized types of taste sensed by humans. Humans receive tastes through sensory organs called taste buds or gustatory calyculi, concentrated on the upper surface of the tongue. Scientists generally describe four basic tastes: bitter, salty, sour, and sweet; a fifth taste, umami, is gaining increasing acceptance. This contrasts markedly with the sense of olfaction or smell, where very large numbers of chemicals, aromatic compounds especially, can be differentiated.
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.Template:Citeneeded
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.Template:Citeneeded
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History
Classically, four tastes are known to be sensed by taste buds: bitter, salty, sour and sweet. Growing in popularity is the concept of a supposed "fifth basic taste" called umami. Five or four basic tastes is the trace of ancient numerology viewpoint. Until recently, most Western sources listed only the first four; in recent years, the fifth taste— umami —has become highly marketed and met with qualified scientific acceptance. 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. The term umami and its status as a supposed "basic taste" were popularized by the MSG industry in the 1980s as a way to dispel health concerns about apparent allergic reactions to MSG. Umami has also recently been equated with "savory," a taste or flavor recognized by British and Dutch food scientists, but not widely accepted in America.
The Chinese also recognize pungent as a sixth flavor. Some argue that spicy should also be included here as a different type of taste. Conflicting opinions exist and there are no reliable studies yet to support this argument. A major problem are confusions between the concept of taste, which generally refers to stimuli directly affecting the tongue, and flavor, which involves olfaction as well.
In general, the sense of taste is often confused by smells that occur at the same time, and much of the apparent sensation of taste is actually derived from smell stimuli. Loss of smell through anosmia, for example when one has a cold, severely reduces one's apparent sense of taste.
Historically, the science of how humans sense taste has been full of misunderstandings and conflicting claims. 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 are generally overly reductionist.
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 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. At the same time, attempts to make a case for new "basic tastes" are often dubious, propelled at least as much by industry marketing as by science.
Umami, it is said, is often found in protein, some vegetables, and fermented foods, such as soy sauce, fish sauce, miso, and black bean sauce. Umami plays a particularly important role in Japanese foods: it is often extracted from fish, sea kelp, and/or shiitake mushrooms to create the Japanese-style soup stock dashi, which is used in many Japanese dishes.
Although umami was not as well recognized in Western countries until recently, many Western dishes supposedly benefit from including umami. For instance, soup stocks, anchovies, some cheeses, and tomato sauce/ketchup, all widely used, are said to contain umami.
However, umami has proven extremely hard to define, and descriptions of it vary from source to source. It includes not only a literal taste but a sensation variously described as "bigness," "impact," "roundness" and so on. There is no doubt that there is some kind of "umami" sensation, but exactly what it is, and whether it is a flavor, a basic taste or some combination of other known basics, is in dispute.
Scientists recently found an umami receptor molecule in tongue tissue. But that doesn't necessarily mean there is a direct umami taste experience due to the way such receptors work. For example, receptors may simply cancel out the sensation of a molecule.
The ancient Chinese Five Elements philosophy lists slightly different five basic tastes: bitter, salty, sour, sweet, and hot instead of umami.
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.
There is a welter of new and ongoing research about taste that continuously puts forth new candidates for "basic" tastes. Other candidates include metallic and an umami-like taste called kokumi.
Many obvious sensations, such at hot, astringent and acidic are still recognized by science, but considered "chemical senses"--mere pain reactions--rather than tastes. Whether that is a meaningful distinction is in dispute.
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.
| 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, such as the under the trademark Bitrex [1], 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 "super-tasters" 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 was used as a medical and flavor additive in the gin and tonic drink.
Umami
Savoriness or umami is the name for the taste sensation produced by the free glutamates commonly found in fermented and aged foods, for example parmesan and roquefort cheeses, as well as soy sauce and fish sauce. It is also found in significant amounts in various unfermented foods such as walnuts, grapes, broccoli, tomatoes, and mushrooms, and to a lesser degree in meat. The glutamate taste sensation is most intense in combination with sodium. This is one reason why tomatoes exhibit a stronger taste after adding salt. Sauces with umami and salty tastes are very popular for cooking, such as tomato sauces and ketchup for Western cuisines and soy sauce and fish sauce for East Asian and Southeast Asian cuisines. However, the lack of umami taste with other glutamate molecules makes at least some experts question what is actually producing the umami taste.
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.
Umami is considered basic in Japanese and Chinese cooking, but is not discussed as much in Western cuisine, where it is sometimes referred to as "savory", "meaty" or "moreish."
The name comes from umami (旨味 or うまみ), the Japanese name for the taste sensation. The characters literally mean "delicious flavor."
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.
The same taste is referred to as xiānwèi (鮮味 or 鲜味) in Chinese cooking.
A subset of umami taste buds responds specifically to glutamate in the same way that sweet ones respond to sugar. Glutamate binds to a variant of G protein coupled glutamate receptors.
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.
Tart
Some food (tea, unripe fruits) contains tannins that constrict organic tissue. The added sensation of astringent substances changes the perception of taste. Synonyms: hard, styptic, rough, harsh (about wine); harsh (about taste).
Spicy
Template:See also 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. Examples of common food ingredients giving this sensation are chile peppers, fruits of the plant Capsicum.
Cold
Some substances activate cold trigeminal receptors. One can sense "cold" from e.g. 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.
Fat
Recent research has revealed a potential taste receptor called the CD36 receptor to be reacting to fat, more specifically, fatty acids. [2] This receptor was found in mice, but probably 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.
References
- Kikunae Ikeda. (1909). New Seasonings
- Bernd Lindemann, Yoko Ogiwara, and Yuzo Ninomiya. (2002). The Discovery of Umami
- Dunlop, Fuschia. '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 - edit |
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| Tongue | Taste bud | Gustatory cortex | Basic tastes |
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