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An appetitive taste,<ref name=aa/> sweetness rewards the consumption of energy-rich sugars.
Sweetness is considered an enjoyable taste in [[The West]],{{Citation needed|date=September 2010}} although it may be less favored in [[Eastern world|The East]].<ref>[http://online.wsj.com/article/SB120958152962857053.html Kraft Reformulates Oreo, Scores in China] wsj.com, MAY 1, 2008</ref> An appetitive taste,<ref name=aa/> it rewards the consumption of energy-rich sugars.


====Measuring relative sweetness====
====Measuring relative sweetness====

Revision as of 04:48, 11 October 2010

Template:Two other uses

Taste bud

Taste (or, more formally, gustation; adjectival form: "gustatory") is a form of direct chemoreception, and is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc.

Humans receive tastes through sensory organs called taste buds[1] or gustatory calyculi, concentrated on the upper surface of the tongue.[2]

The sensation of taste is traditionally broken into basic tastes: sweetness, bitterness, sourness, saltiness, etc. Umami is a basic taste,[3] although only recently recognized as such in The West.[4]

As taste senses both harmful and beneficial things, all basic tastes are classified as either appetitive or aversive, depending upon the effect the things they sense have on our bodies.[5]

The basic tastes only partially contribute to the sensation and flavor of food in the mouth—other factors include smell,[1] detected by the olfactory epithelium of the nose;[6] texture,[7][8] detected through a variety of mechanoreceptors, muscle nerves, etc.;[9] and temperature, detected by thermoreceptors.

History

In The West, Aristotle, who postulated c. 350 BCE[10] that the two most basic tastes were sweet and bitter,[11] was one of the first to develop a list of basic tastes.[12]

Ayurveda, an ancient Indian healing science, has its own tradition of basic tastes, including: astringent, bitter, pungent, salty, sour, and sweet.[13][14]

Recent discoveries

The receptors for all known basic tastes have been identified. Sour and salty are detected with ion channels while the receptors for sweet, bitter, and umami are G protein coupled receptors.[15]

There is some evidence for a sixth basic taste that senses fatty substances.[16][17][18]

Taste-map myth

All taste sensations arise from all regions of the tongue despite a common misconception that different sections of the tongue specialized in different tastes.[4][19]

Basic tastes

While the human tongue may be able to identify many thousands of different tastes, all these can be grouped into a few primary kinds. In The West[citation needed] these basic tastes have traditionally been: bitter, salty, sour, and sweet.[4] Four categories has been recognized as insufficient,[a][4][20][21] however, and umami has recently seen inclusion to this list.[4][21][22] Piquance is considered another such basic taste in The East.[22]

Bitter

Bitterness is perceived by many to be unpleasant. An aversive taste,[5] it helps prevent ingestion of toxic substances.[23][24]

Measuring relative bitterness

Quinine, a bitter medicinal found in tonic water, can be used to subjectively rate the bitterness of a substance.[25] Units of dilute quinine hydrochloride (1g in 2000mL of water) can be used to measure the threshold bitterness concentration, the level at which the presence of a dilute bitter substance can be detected by a human taster, of other compounds.[25] More formal chemical analysis, while possible, is difficult.[25]

Functional structure

Research has shown that TAS2Rs (taste receptors, type 2, also known as T2Rs) such as TAS2R38, are responsible for the human ability to taste bitter substances.[26] They are identified not only by their ability to taste certain bitter ligands, but also by the morphology of the receptor itself (surface bound, monomeric).[27]

A protective sense

The ability to detect bitter-tasting substances at low thresholds is considered to provide an important protective function because many toxins taste bitter.[23][24][28]

Salty

Saltiness is the taste of salt. An appetitive taste,[5] it drives the consumption of salt.

Measuring relative saltiness

Relative saltiness can be rated by comparison to a dilute salt solution.[29]

Functional structure

Saltiness is a taste produced best by the presence of sodium ions,[citation needed] and, like sour, it is tasted using ion channels.[30]

Other ions of the alkali metals group also taste salty, but the less sodium-like the ion is, the less salty the sensation. The size of lithium and potassium ions most closely resemble that of sodium, so they taste similar to salt. In contrast the larger rubidium and cesium ions do not taste as salty.[citation needed]

Other monovalent cations, e.g. ammonium, NH4+, and divalent cations of the alkali earth metal group of the periodic table, e.g. calcium, Ca2+, ions generally elicit a bitter rather than a salty taste even though they, too, can pass directly through ion channels in the tongue, generating an action potential.[citation needed]

Sour

Sour is a basic taste that is considered agreeable only in small amounts. An aversive taste, it wards off the ingestion of harmful substances.[5]

Measuring relative sourness

The sourness of a substance can be rated by comparing it to dilute hydrochloric acid (HCl).[citation needed]

Functional structure

Sourness is acidity,[31][32] and, like salt, it is a taste sensed using ion channels.[30] Hydrogen ion channels detect the concentration of hydronium ions that are formed from acids and water.[citation needed] Additionally, the taste receptor PKD2L1 has been found to be involved in tasting sour.[33]

Sour candy

Sour candy is popular in North America.[34]

Sweet

Sweetness is considered an enjoyable taste in The West,[citation needed] although it may be less favored in The East.[35] An appetitive taste,[5] it rewards the consumption of energy-rich sugars.

Measuring relative sweetness

Sweetness is subjectively measured by comparing the threshold values, or level at which the presence of a dilute substance can be detected by a human taster, of different sweet substances.[36] Substances are usually measured relative to sucrose,[37] which is usually given an arbitrary index of 1[38][39] or 100.[40] Fructose is about 1.4 times sweeter than sucrose; glucose, a sugar found in honey and vegetables, is about three-quarters as sweet; and lactose, a milk sugar, is one-half as sweet.[b][36]

Functional structure

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 a carbonyl group. Sweetness is detected by a variety of G protein coupled receptors coupled to a G protein that acts as an intermediary in the communication between taste bud and brain, gustducin.[41] These receptors are T1R2+3 (heterodimer) and T1R3 (homodimer), which account for sweet sensing in humans and animals.[42]

Umami

Umami can be tasted in cheese[22] and soy sauce,[4] and while it is found in many other fermented and aged foods this savory taste is also present in tomatoes, grains and beans.[22]

Although considered fundamental to many Eastern cuisines[43] and first described in 1908,[44] it was only recently recognized in The West.[4][45] An appetitive taste,[5] it facilitates ingestion of protein-rich food.[citation needed]

Functional structure

An amino acid, glutamic acid, is responsible for umami,[3][46] but some nucleotides (inosinic acid[43][47] and guanylic acid[3]) can act as complements, enhancing the taste.[43][47]

Glutamic acid binds to a variant of the G protein coupled receptor, producing an umami taste.[48][49]

MSG

The food additive monosodium glutamate (MSG), developed as a food additive in 1908 by Kikunae Ikeda,[50][51][52] produces a strong umami taste.[4]

Further sensations

The tongue can also feel other sensations, not generally included in the basic tastes. These are largely detected by the somatosensory system.

Fattiness

Recent research has revealed a potential taste receptor called the CD36 receptor to be reacting to fat, more specifically, fatty acids.[53] This receptor was found in mice, but probably exists among other mammals as well. In experiments, mice with a genetic defect that blocked this receptor didn't show the same urge to consume fatty acids as normal mice, and 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 behaviour, although more research is still necessary to confirm the relationship between CD36 and the perception of fat.

Calcium

In 2008, geneticists discovered a CaSR calcium receptor on the tongues of mice. The CaSR receptor is commonly found in the gastrointestinal tract, kidneys and brain. Along with the "sweet" T1R3 receptor, the CaSR receptor can detect calcium as a taste. Whether closely related genes in mice and humans means the phenomenon may exist in humans as well is unknown.[54][55]

Dryness

Some foods, such as unripe fruits, contain tannins or calcium oxalate that cause an astringent or rough sensation of the mucous membrane of the mouth or the teeth. Examples include tea, red wine, rhubarb, and unripe persimmons and bananas.

Less exact terms for the astringent sensation are "dry", "rough", "harsh" (especially for wine), "tart" (normally referring to sourness), "rubbery", "hard" or "styptic".[56]

In the Indian tradition, one of the 6 tastes [57] is astringency (Kasaaya in Sanskrit, the other five being sweet, sour, salty, bitter, and hot/pungent).

In wine terms, "dry" is the opposite of "sweet," and does not refer to astringency. Wines that contain tannins and that cause astringent sensations in the mouth are not necessarily classified as "dry," and "dry" wines are not necessarily astringent.

Prickliness or hotness

Substances such as ethanol and capsaicin cause a burning sensation by inducing a trigeminal nerve reaction together with normal taste reception. The sensation of heat is caused by the food activating nerves that express TRPV1 and TRPA1 receptors. Two main plant derived compounds that provide this sensation are capsaicin from chili peppers and piperine from black pepper. The piquant ("hot" or "spicy") sensation provided by chili peppers, black pepper, and other spices like ginger and horseradish plays an important role in a diverse range of cuisines across the world—especially in equatorial and sub-tropical climates, such as Ethiopian, Peruvian, Hungarian, Indian, Korean, Indonesian, Lao, Malaysian, Mexican, Southwest Chinese (including Sichuan cuisine), and Thai cuisines.

If tissue in the oral cavity has been damaged or sensitised, ethanol may be experienced as pain rather than simply heat. Those who have had radiotherapy for oral cancer thus find it painful to drink alcohol.[citation needed]

This particular sensation is not a taste in the technical sense, because a different set of nerves carry it to the brain. Though foods like chili peppers also activate nerves, the sensation interpreted as "hot" results from the stimulation of somatosensory (pain/temperature) fibers on the tongue. Many parts of the body with exposed membranes but without taste sensors (such as the nasal cavity, under the fingernails, or a wound) produce a similar sensation of heat when exposed to hotness agents. In Asian countries within the sphere of mainly Chinese, Indian, and Japanese cultural influence, Piquance has traditionally been considered a sixth basic taste.

Coolness

Some substances activate cold trigeminal receptors. One can sense a cool sensation (also known as "fresh" or "minty") from, e.g., spearmint, menthol, ethanol or camphor, which is caused by the food activating the TRPM8 ion channel on nerve cells that also signal cold. Unlike the actual change in temperature described for sugar substitutes, coolness is only a perceived phenomenon.

Numbness

Both Chinese and Batak Toba cooking include the idea of 麻 , or mati rasa the sensation of tingling numbness caused by spices such as Sichuan pepper. The cuisine of Sichuan province in China and of North Sumatra province in Indonesia, often combines this with chili pepper to produce a 麻辣 málà, "numbing-and-hot", or "mati rasa" flavor.[58]

Heartiness (Kokumi)

Some Japanese researchers refer to the kokumi in foods laden with alcohol- and thiol-groups in their amino acid extracts, which has been described variously as continuity, mouthfulness, mouthfeel, and thickness.

Temperature

Temperature is an essential element of human taste experience. Food and drink that—within a given culture—is considered to be properly served hot is often considered distasteful if cold, and vice versa.

Some sugar substitutes have strong heats of solution, as is the case of sorbitol, erythritol, xylitol, mannitol, lactitol, and maltitol. When they are dry and are allowed to dissolve in saliva, heat effects can be recognized. The cooling effect upon eating may be desirable, as in a mint candy made with crystalline sorbitol, or undesirable if it's not typical for that product, like in a cookie. Crystalline phases tend to have a positive heat of solution, and thus a cooling effect. The heats of solution of the amorphous phases of the same substances are negative, and cause a warm impression in the mouth.[59]

Supertasters

A supertaster is a person whose sense of taste is significantly more sensitive than average. The cause of this heightened response is thought to be, at least in part, due to an increased number of fungiform papillae.[60]

Aftertaste

Aftertastes arise after food has been swallowed. An aftertaste can differ from the food it follows. Medicines and tablets may also have a lingering aftertaste, as can certain artificial flavor compounds, such as aspartame (artificial sweetener).

Acquired taste

An acquired taste is an appreciation for a food or beverage that is unlikely to be enjoyed at first taste. Many of the world's delicacies are considered to be acquired tastes.

Innervation

Taste is brought to the brainstem by 3 different cranial nerves:

Disorders of taste

See also

Further reading

Notes

a. ^ It has been known for some time that these categories may not be comprehensive. In Guyton's 1976 edition of Textbook of Medical Physiology, he wrote:

On the basis of physiologic studies, there are generally believed to be at least four primary sensations of taste:sour, salty, sweet, and bitte. Yet we know that a person can perceive literally hundreds of different tastes. These are all supposed to be combinations of the four primary sensations...However, there might be other less conspicuous classes or subclasses of primary sensations",[61]

b. ^ Some variation in values is not uncommon between various studies. Such variations may arise from a range of methodological variables, from sampling to analysis and interpretation. In fact there is a "plethora of methods"[62] Indeed, the taste index of 1, assigned to reference substances such as sucrose (for sweetness), hydrochloric acid (for sourness), quinine (for bitterness), and sodium chloride (for saltiness), is itself arbitrary for practical purposes.[63]

Some values, such as those for maltose and glucose, vary little. Others, such as aspartame and sodium saccharin, have much larger variation. Regardless of variation, the perceived intensity of substances relative to each reference substance remains consistent for taste ranking purposes. The indices table for McLaughlin & Margolskee (1994) for example,[28][64] is essentially the same as that of Svrivastava & Rastogi (2003),[65] Guyton & Hall (2006),[63] and Joesten et al (2007).[38] The rankings are all the same, with any differences, where they exist, being in the values assigned from the studies from which they derive.

As for the assignment of 1 or 100 to the index substances, this makes no difference to the rankings themselves, only to whether the values are displayed as whole numbers or decimal points. Glucose remains about three-quarters as sweet as sucrose whether displayed as 75 or 0.75.

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