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Sweetness is one of the five basic tastes and is universally regarded as a pleasurable experience, except perhaps in excess. Foods rich in simple carbohydrates such as sugar are those most commonly associated with sweetness, although there are other natural and artificial compounds that are sweet at much lower concentrations, allowing their use as non-caloric sugar substitutes. Examples of foods that may be used as non-sugar sweet substitutes include saccharin, aspartame, acesulfame potassium, sucralose, xylitol, erythritol, and stevia. Other compounds, such as miraculin, may alter perception of sweetness itself. The chemosensory basis for detecting sweetness, which varies between both individuals and species, has only begun to be understood since the late 20th century. One theoretical model of sweetness is the multipoint attachment theory, which involves multiple binding sites between a sweetness receptor and a sweet substance. Studies indicate that responsiveness to sugars and sweetness has very ancient evolutionary beginnings, being manifest as chemotaxis even in motile bacteria such as ''E. coli''.〔Blass, E.M. ''Opioids, sweets and a mechanism for positive affect: Broad motivational implications.'' 〕 Newborn human infants also demonstrate preferences for high sugar concentrations and prefer solutions that are sweeter than lactose, the sugar found in breast milk. Sweetness appears to have the highest taste recognition threshold, being detectable at around 1 part in 200 of sucrose in solution. By comparison, bitterness appears to have the lowest detection threshold, at about 1 part in 2 million for quinine in solution. In the natural settings that human primate ancestors evolved in, sweetness intensity should indicate energy density, while bitterness tends to indicate toxicity The high sweetness detection threshold and low bitterness detection threshold would have predisposed our primate ancestors to seek out sweet-tasting (and energy-dense) foods and avoid bitter-tasting foods. Even amongst leaf-eating primates, there is a tendency to prefer immature leaves, which tend to be higher in protein and lower in fibre and poisons than mature leaves. The 'sweet tooth' thus has an ancient evolutionary heritage, and while food processing has changed consumption patterns,〔Fischler, C. ''Attitudes towards sugar and sweetness in historical and social perspective.'' 〕 human physiology remains largely unchanged. ==Examples of sweet substances== A great diversity of chemical compounds, such as aldehydes and ketones are sweet. Among common biological substances, all of the simple carbohydrates are sweet to at least some degree. Sucrose (table sugar) is the prototypical example of a sweet substance. Sucrose in solution has a sweetness perception rating of 1, and other substances are rated relative to this. For example, another sugar, fructose, is somewhat sweeter, being rated at 1.7 times the sweetness of sucrose.〔 Some of the amino acids are mildly sweet: alanine, glycine, and serine are the sweetest. Some other amino acids are perceived as both sweet and bitter. A number of plant species produce glycosides that are sweet at concentrations much lower than sugar. The most well-known example is glycyrrhizin, the sweet component of licorice root, which is about 30 times sweeter than sucrose. Another commercially important example is stevioside, from the South American shrub ''Stevia rebaudiana''. It is roughly 250 times sweeter than sucrose. Another class of potent natural sweeteners are the sweet proteins such as thaumatin, found in the West African katemfe fruit. Hen egg lysozyme, an antibiotic protein found in chicken eggs, is also sweet. Even some inorganic compounds are sweet, including beryllium chloride and Lead(II) acetate. The latter may have contributed to lead poisoning among the ancient Roman aristocracy: the Roman delicacy ''sapa'' was prepared by boiling soured wine (containing acetic acid) in lead pots. Hundreds of synthetic organic compounds are known to be sweet. The number of these that are legally permitted as food additives is, however, much smaller. For example, chloroform, nitrobenzene, and Ethylene glycol are sweet, but also toxic. , seven artificial sweeteners are in widespread use: saccharin, cyclamate, aspartame, acesulfame potassium, sucralose, alitame, and neotame. However cyclamate is banned in the US since 1969.〔http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/FoodAdditiveListings/ucm091048.htm#ftnC〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「sweetness」の詳細全文を読む スポンサード リンク
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