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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 describe five basic tastes: bitter, salty, sour, sweet, and umami. The last, (the flavor of certain glutamates, variously described as savoury, meaty, or brothy) has long been known in Asian cooking, but has only recently been found to have its own taste receptors.

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.[How to reference and link to summary or text]

Psychologists speak more about "flavour 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.[How to reference and link to summary or text]

Ancient historyEdit

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 flavour, which involves olfaction as well. Many obvious sensations, such as 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. In fact, taste qualities are found in all areas of the tongue, in contrast with the popular view that different tastes map to different areas of the tongue. [1] [2]

Recent discoveries Edit

In recent years, advances in chemistry and food research have led to suggestions of additional basic food flavours. The most well-known and generally accepted is the concept of a "fifth basic taste" called savoury, or "umami". Savoury is generally described as the taste of the common food flavouring 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 savoury taste is produced by interaction of NMDA and mGluR4 receptors [1].

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 flavour called kokumi which has been described variously as continuity, "mouthfulness", and thickness.

In Indian tradition, the tastes are referred to as 'Arusuvai' or six tastes [2]. These tastes are normally referred to as the following: sweet, sour, salty, bitter, hot / spicy and astringent. Some people call the sixth taste as neutral or tasteless. Typical example of neutral is water. Certain others say the astringent or the sixth taste is a mix of varied tastes and is termed Kasaaya, in India. That is more in line with the Japanese approach to umami.

Main five basic tastes Edit

SaltinessEdit

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.

SournessEdit

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.

SweetnessEdit

Main article: Sweetness

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.

See also: Miraculin and Curculin

Bitterness Edit

The bitter taste is perceived by many to be unpleasant, sharp, or disagreeable. Evolutionary biologists have suggested that a distaste for bitter substances may have evolved as a defense mechanism against accidental poisoning. Indeed bitterants are commonly used as aversive agents to discourage the inhalation or ingestion of toxic substances.

However, not all bitter substances are harmful; coffee and tonic water are both popular, bitter beverages. Other common bitter foods include bitter melon, arugula, watercress, and dandelion. Quinine, the anti-malarial prophylactic, is also known for its bitter taste and is found in tonic water.

The bitterest substance known is the synthetic chemical denatonium, discovered in 1958 and today marketed as the trademarked Bitrex [3]. It is a white, odourless solid used as an aversive agent that is often added to toxic substances to prevent accidental ingestion.

Research has shown that TAS2Rs (taste receptors, type 2) coupled to the G protein gustducin are responsible for the human ability to taste bitter substances. 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)[3]. Researchers use two synthetic substances, phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) to study the genetics of bitter perception. These two substances taste bitter to some people, but are virtually tasteless to others. Among the tasters, some are so-called "supertasters" to whom PTC and PROP are 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.

Savouriness Edit

Main article: umami

Savouriness 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 Japanese, the term umami (旨味, うまみ) 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 xiānwèi (鮮味 or 鲜味) in Chinese cooking. Savoury is considered a fundamental taste in Japanese and Chinese cooking, but is not discussed as much in Western cuisine.

Examples 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.

The 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 [4].

Other sensationsEdit

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.

TemperatureEdit

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, besides the sweet taste also 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. [5]

(False) coolnessEdit

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 phenomenon.

Spiciness or (false) heatEdit

See also: Scoville scale

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, Indonesian and Thai 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. The term pungent is also used for this, especially among people of Anglo-Indian ethnicity. Indeed, many languages have a specific term, e.g. Chinese 辣 (), Dutch pikant, Finnish tulinen, Hungarian csípős, Italian piccante, Japanese 辛い (karai), Korean 맵다 (maepda), Polish (pikantny, ostry), Russian острый (ostryi), Spanish picante, Swedish stark, Thai เผ็ด (phet), and Vietnamese cay.

Astringency Edit

Some foods, such as tea or unripe fruits, contain tannins that constrict organic tissue. The best examples of this are unripe persimmons and bananas, 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). The Chinese have a term for this: 澀 (), the Korean have 떫다 (tteolda), the Japanese call it 渋い (shibui), while Thai have ฝาด (fard), and in Russian there is вяжущий (vyazhuschiy).

FatEdit

Recent research has revealed a potential taste receptor called the CD36 receptor to be reacting to fat, more specifically, fatty acids. [6] 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 of CD36 and the cravings of fat.

Tingly numbnessEdit

Chinese cooking includes the idea of 麻 , the sensation of tingling numbness caused by spices such as Sichuan pepper. The cuisine of Sichuan province often combines this with chili to produce a 麻辣 málà, "numbing-and-hot", flavour. [7]

References Edit

  1. Huang A. L., et al. "The cells and logic for mammalian sour taste detection"., Nature, 442. 934 - 938 (2006).
  2. Scenta. How sour taste buds grow. URL accessed on August 28, 2006.
  3. Lindemann "Receptors and transduction in taste." Nature 2001
  4. Lindemann, Bernd (2000). A taste for umami. Nature Neuroscience.
  5. Cammenga, HK, LO Figura, B Zielasko (1996). Thermal behaviour of some sugar alcohols. Journal of thermal analysis 47 (2): 427-434.
  6. http://www.sciam.com/article.cfm?chanID=sa003&articleID=000AFE88-E770-1367-A6B083414B7F4945
  7. http://www.uni-graz.at/~katzer/engl/Zant_pip.html?noframes]

External links Edit

Sensory system - Gustatory system - edit
Tongue | Taste bud | Gustatory cortex | Basic tastes
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