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Food is valued greatly by its taste. In tasting a food the taste buds plays a major role they perceive the taste and register subsequently foods are categorised as sweet, salt, sour or bitter.
Taste budscontain the receptors for taste. They are located around the small structures on the upper surface of thetongue,soft palate, upperesophagus and epiglottis, which are called papillae. 
The papillae are involved in detecting the five (known) elements of taste perception: salty, sour, bitter, sweet, and savory (or umami). Via small openings in the tongue epithelium, called taste pores, parts of the food dissolved in saliva come into contact with taste receptors. These are located on top of the taste receptor cells that constitute the taste buds. The taste receptor cells send information detected by clusters of various receptors and ion channels to the gustatory areas of the brain via the seventh, ninth and tenth cranial nerves.
The upper surface of the tongue, showing kinds of papillae and areas of taste.
Taste buds near the tip of the tongue are more sensitive to sweet and salt. Those on the sides to sour and those near the back to bitter. The presence of particular compounds in foods are responsible for the different tastes.
For example the sour sensation is associated with hydrogen ions supplied by acids like vinegar and by those found in fruits and vegetables.
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 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 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.
itterness is the taste which detects bases. 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.
Savouriness(umami) 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 the Japanese, the term umami is used for this taste sensation, whose characters literally mean "delicious flavour." Umami is now the commonly used term by taste scientists. 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
Astringency is dry puckery sensation believed to be due to precipitation of the proteins in the saliva and in the mucous membrane lining of the mouth which deprives them of their lubricating character. Astringent substances may also constrict the ducts leading from the salivary glands to the mouth. Unripe fruits-like cashew fruit, wood apple, blueberry and gooseberry are astringent..
Taste interactions:Having described the five basic tastes it is obvious that foods are a very complex system which contain many different taste compounds and therefore many different tastes. The fact that there are only five basic tastes and yet we are able to detect hundreds of different taste sensations is due to a series of complex taste interactions that can range from simple two way interactions to complex five way interactions between the four basic tastes were previously described simplistically by the taste tetrahedron.
The minimum concentration that is required to identify a taste is known as threshold. The sensitivity to the five taste sensations differ in individuals consequently the threshold for each of the primary tastes is usually not at the same level in any one individual.
The pleasant sensations in eating comes more from odour than from taste.
Taste interaction: Foods contain a mixture of substances which elicit all four taste sensations. Salt in sub threshold concentration reduces the tartness of acid. Some threshold concentrations of salt also increase the apparent sweetÂness of sucrose. The addition of salt to lime juice, sherbet, lassi, and to fruits like apple or guava improve the taste.
Conversely acids in sub threshold concentration intensify the saltiness of sodium chloride so it is easy to cover salt tart foods. Sugar in sub threshold concentration reduces the saltiness of sodium chloride so a pinch of sugar may improve vegetable soup that has been over salted. Sugar also reduces the sourness of acids and the bitterness of coffee.
Mouthfeel: It is the result of product’s physical and chemical interaction in the mouth. It is evaluated from initial perception on the palate, to first bite, through mastication to swallowing and aftertaste. For example in wine-tasting, mouth feel is usually used with a modifier (big, sweet, tannic, chewy, etc.) to the general sensation of the wine in the mouth. Some people, however, use the traditional term, "texture". Mouthfeel is often related to a product's moisture content hard or crisp products having lower moisture and soft products having intermediate to high moisture content.
Texture and consistency and hotness or burning sensation of pepper can be felt in the mouth.
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