Sweetness
Sweetness is a basic taste most commonly perceived when eating foods rich in sugars.
The perceived intensity of sugars and high-potency sweeteners, such as aspartame and neohesperidin dihydrochalcone, are heritable, with gene effect accounting for approximately 30% of the variation.
[1] The chemosensory basis for detecting sweetness, which varies between both individuals and species, has only begun to be understood since the late 20th century.
Studies indicate that responsiveness to sugars and sweetness has very ancient evolutionary beginnings, being manifest as chemotaxis even in motile bacteria such as E.
[3][4] 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.
[5] In the natural settings that human primate ancestors evolved in, sweetness intensity should indicate energy density, while bitterness tends to indicate toxicity.
[9] The "sweet tooth" thus has an ancient heritage, and while food processing has changed consumption patterns,[10][11] human physiology remains largely unchanged.
[16] A number of plant species produce glycosides that are sweet at concentrations much lower than common sugars.
Another class of potent natural sweeteners are the sweet proteins such as thaumatin, found in the West African katemfe fruit.
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.
[28] Gymnemic acid has been widely promoted within herbal medicine as a treatment for sugar cravings and diabetes.
[31] Human studies have shown that sweet taste receptors are not only found in the tongue, but also in the lining of the gastrointestinal tract as well as the nasal epithelium, pancreatic islet cells, sperm and testes.
[32] It is proposed that the presence of sweet taste receptors in the GI tract controls the feeling of hunger and satiety.
Another research has shown that the threshold of sweet taste perception is in direct correlation with the time of day.
[43] The development of organic chemistry in the 19th century introduced many new chemical compounds and the means to determine their molecular structures.
Early organic chemists tasted many of their products, either intentionally (as a means of characterization) or accidentally (due to poor laboratory hygiene).
One of the first attempts to draw systematic correlations between molecules' structures and their tastes was made by a German chemist, Georg Cohn, in 1914.
Simply put, they proposed that to be sweet, a compound must contain a hydrogen bond donor (AH) and a Lewis base (B) separated by about 0.3 nanometres.
