Taste

Taste (or, more formally, gustation; adjectival form: "gustatory") 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, or gustatory calyculi, concentrated on the upper surface of the tongue.

The sensation of taste is traditionally broken into basic tastes: sweetness, bitterness, sourness, saltiness, etc. Umami is a basic taste,

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.

The basic tastes only partially contribute to the sensation and flavor of food in the mouth—other factors include smell, texture, detected through a variety of mechanoreceptors, muscle nerves, etc.; and temperature, detected by thermoreceptors.

Introduction

As one of the senses, taste is an essential part of daily life.

History

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

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

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.

There is some evidence for a sixth taste that senses fatty substances.

Bitter taste receptors (TAS2Rs) are also expressed in lung tissue. Bitter substances showed bronchodilative effects by localized calcium signaling, and are now seen as promising agents for the development of new asthma drugs.

Taste-map myth

Despite a common misconception that different sections of the tongue specialized in different tastes, all taste sensations come from all regions of the tongue.

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 these basic tastes have traditionally been: bitter, salty, sour, and sweet. however, and umami has recently seen inclusion to this list. Piquance is considered another such basic taste in The East.

Salty

Saltiness is the taste of salt. An appetitive taste, brothy or meaty taste. Umami can be tasted in cheese and soy sauce, produces a strong umami taste. Although considered fundamental to many Eastern cuisines it was only recently recognized in the West as a basic taste. More formal chemical analysis, while possible, is difficult.

The sourness of a substance can be rated by comparing it to very dilute hydrochloric acid (HCl).

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. Substances are usually measured relative to sucrose, which is usually given an arbitrary index of 1 or 100. 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. 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).

;Saltiness: Saltiness is a taste produced best by the presence of cations (such as , or ) and, like salt, it is a taste sensed using ion channels. Hydrogen ion channels detect the concentration of hydronium ions that are formed from acids and water. Additionally, the taste receptor PKD2L1 has been found to be involved in tasting sour.

;Sweetness: Sweetness is produced by the presence of sugars, some proteins, and a few other substances. It 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. These receptors are T1R2+3 (heterodimer) and T1R3 (homodimer), which account for sweet sensing in humans and animals.

;Umami-ness: An amino acid, glutamic acid, is responsible for umami, but some nucleotides (inosinic acid

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

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. 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.

;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".

In the Indian tradition, one of the 6 tastes 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 Szechuan 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.

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 má, 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.

;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.

Other concepts

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.

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:

Facial Nerve for the anterior 2/3 of the tongue.

Glossopharyngeal Nerve for the posterior 1/3 of the tongue.

Vagus Nerve for the small area on the epiglottis.

Disorders of taste

ageusia (complete loss of taste)

dysgeusia (persistent abnormal taste)

See also

Palatability

Optimal foraging theory

Vomeronasal organ

Further reading

Alternative ISBN 978-1-57331-738-2 Paperback ISBN 1-57181-970-3 Alternative ISBN 3-13-107261-X

Notes

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" 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.

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, is essentially the same as that of Svrivastava & Rastogi (2003), Guyton & Hall (2006),

References

External links

Researchers Define Molecular Basis of Human "Sweet Tooth" and Umami Taste

Statistics on Taste at National Institute on Deafness and Other Communication Disorders. An informative overview with good list of references.

Category:Articles with inconsistent citation formats Category:Sensory system Category:Gustation Category:Gustatory system