Sweetness

Sweetness is a basic taste most commonly perceived when eating foods rich in sugar. Sweet tastes are generally regarded as pleasurable. In addition to sugars like sucrose, many other chemical compounds are sweet, including aldehydes, ketones, and sugar alcohols. Some are sweet at very low concentrations, allowing their use as non-caloric sugar substitutes. Such non-sugar sweeteners include saccharin, aspartame, sucralose and stevia. Other compounds, such as miraculin, may alter perception of sweetness itself.
Sweetness is one of the five basic taste qualities and it mostly involves foods with sugars. It is known to be enjoyable and it is an important factor for food choices beyond cultures. Furthermore, sugars like sucrose, there are many other organic and inorganic compounds that bring out a sweet taste. This involves aldehydes, ketones, amino acids, and other artificial sweeteners. Sweetness recognition in our bodies takes part in an important role in energy control and evolutionary behavior.
New research has proven that sweetness does not only involve taste receptors on the tongue but includes metabolic sensing, gut brain signaling, and post-ingestive rewards.
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.
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.
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.

Origin and evolution

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.
In the beginning, human ancestors progressed in strong preferences for sweet foods. Sweet taste includes the highest detection thresholds, which means that there are high concentrations that are required before the sweetness is perceived. This made sweetness an important role for caloric value. On the other hand, bitterness has one of the lowest detection thresholds, and is an early warning signal for toxins.
Sweetness is linked with humans' ecological needs. An example involves leaf-eating primates who prefer sweeter leaves because they have more protein and less compounds. Food processing in modern society has changed consumption patterns, but the biological preference for sweetness has remained.
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 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 heritage, and while food processing has changed consumption patterns, human physiology remains largely unchanged. Biologically, a variant in fibroblast growth factor 21 increases craving for sweet foods.
Sweetness is known as one of the five basic taste qualities, along with sourness, saltiness, bitterness, and umami. Each taste is linked with its own specialized receptors that help the body to detect nutrients which is important for survival. Sweetness is linked to energy-rich carbohydrates, whereas umami is linked to amino acids like glutamate. The recognition of umami as a basic taste comes from biochemical receptor discoveries that are similar to those that clarified sweetness signaling. This comparison shows how sweetness functions as a coordinated system of taste perception that helps appetites and nutrient intake.
Across human societies, sweetness has had a lot of meanings that are not just related to the role of taste quality. Anthropologists have explained that many cultures have linked sweet foods with celebration and generosity. Even before large scale sugar production, sweet ingredients like honey, dates and fruit syrups were reserved for communal feasting. These foods were difficult to have at the time and because of this their rarity made sweetness fall into a luxury category. Over time, as sugar become available through global trade, sweet foods have shifted from privileges to everyday samples and this has caused changes in diets and many traditions.

Examples of sweet substances

Examples of Sweet Substances
Different parts of compounds can stimulate sweetness, including:

Simple carbohydrates: glucose, fructose, sucrose.
Amino Acids: glycine, L-alanine, L-serine.
Sugar alcohols: sorbitol, xylitol.
Natural glycosides: stevioside, glycyrrhizin.
Sweet proteins: thaumatin and monellin.

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 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 amino acids are mildly sweet: of the proteinogenic amino acids, L-alanine, glycine, L-proline and L-serine are the sweetest. Some other amino acids, such as L-valine, are perceived as both sweet and bitter. Additionally, many D- enantiomers of proteinogenic amino acids have a sweet taste, even when their L- enantiomer lacks any sweet taste, such as in the case of D-asparagine versus L-asparagine.
The sweetness of 5% solution of glycine in water compares to a solution of 5.6% glucose or 2.6% fructose.
A number of plant species produce glycosides that are sweet at concentrations much lower than common sugars. 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.

Name	Type of compound	Sweetness
Lactose	Disaccharide	0.16
Maltose	Disaccharide	0.33 – 0.45
Trehalose	Disaccharide	max. 0.45
Isomaltulose	Disaccharide	0.40 - 0.50
L-serine	Amino acid	0.53 – 0.55
L-proline	Amino acid	0.37 – 0.76
Sorbitol	Polyalcohol	0.6
Galactose	Monosaccharide	0.65
Glucose	Monosaccharide	0.74 – 0.8
Glycine	Amino acid	0.6 – 0.89
L-alanine	Amino acid	0.77 – 1.10
Sucrose	Disaccharide	1.00
Xylitol	sugar alcohol	1.02
Fructose	Monosaccharide	1.17 – 1.75
Sodium cyclamate	Sulfonate	26
Steviol glycoside	Glycoside	40 – 300
Aspartame	Dipeptide methyl ester	180 – 250
Acesulfame potassium	Oxathiazinone dioxide	200
Sodium saccharin	Sulfonyl	300 – 675
Sucralose	Modified disaccharide	600
Monellin	Protein	800 to 2000
Thaumatin	Protein	2000
Neotame	Aspartame analog	8000
Sucrooctate	Guanidine	162,000
Bernardame	Guanidine	188,000
Sucrononic acid	Guanidine	200,000
Carrelame	Guanidine	200,000
Lugduname	Guanidine	230,000

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. Indeed, the taste index of 1, assigned to reference substances such as sucrose, hydrochloric acid, quinine, and sodium chloride, 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.
Even some inorganic compounds are sweet, including beryllium chloride and lead acetate. The latter may have contributed to lead poisoning among the ancient Roman aristocracy: the Roman delicacy sapa was prepared by boiling soured wine in lead pots.
Hundreds of synthetic organic compounds are known to be sweet, but only a few of these are legally permitted as food additives. For example, chloroform, nitrobenzene, and ethylene glycol are sweet, but also toxic. Saccharin, cyclamate, aspartame, acesulfame potassium, sucralose, alitame, and neotame are commonly used.