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Sugar alcohol

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Definition

noun

plural: sugar alcohols


A polyol resulting from the reduction of the carbonyl group in a sugar to a hydroxyl group




Details

Overview

A polyol is an alcohol characterized by the presence of three or more hydroxyl groups (thus, the name). The term "poly" means multiple and –"ol" refers to alcohol. Sugar alcohol belongs to a class of polyols that are derived typically from sugars. Sugar alcohols are white, water-soluble solids. Their general chemical formula is (CHOH)nH2, where n may range from 3 or more.


Structure/Characteristics

Sugar alcohols, just like other polyols and sugars, are organic compounds. An organic compound is a compound that, in general, contains carbon covalently bound to other atoms, especially Carbon-Carbon and Carbon-Hydrogen. Sugar alcohols may occur naturally or produced industrially. For instance, they may be produced by the hydrogenation of sugars. However, they are not "true sugars". Sugars are monosaccharides and disaccharides that have a general chemical formula of Cn(H2O) n. Sugar alcohols are structurally similar to sugars but they have additional hydroxyl groups. They are also similar to sugars in a way that they, too, may act as an energy source. They are less sweet than sugars.


Biological reaction

Polyol pathway

The polyol pathway is a biological process wherein glucose is converted into fructose. It is called polyol because glucose is first reduced to a polyol sorbitol. Sorbitol is then oxidized to fructose. The reduction of glucose to sorbitol is catalyzed by the enzyme aldose reductase whereas the oxidation of sorbitol to fructose is catalyzed by the enzyme sorbitol dehydrogenase. The pathway makes use of cofactors, NADPH and NAD+.


This pathway is implicated in type-II diabetes complications, such as microvascular damage to insulin-independent cells of kidney, retina, and nerves.[1] Glucose that has not been phosphorylated by the enzyme hexokinase for glycolytic pathway normally enters the polyol pathway to be converted into fructose. However, when there is a large amount of excess glucose, such as in diabetic conditions, the hexokinase becomes saturated with the overwhelming amount of glucose, and consequently, glucose is reduced to sorbitol by aldose reductase instead. Since more NADPH and NAD+ are used in the polyol pathway, they become less available for other important metabolic activities, e.g. glutathione and nitric oxide production. It also leads to increased reactive oxygen species, which can be damaging to cells.


Biological importance

Sugar alcohols are biologically important as they are involved in certain metabolic pathways. Sorbitol, for instance, is a substrate in polyol pathway where unused glucose is reduced into sorbitol, which in turn, is oxidized to produce fructose. Fructose is an essential monosaccharide since it is used in certain metabolic activities of the cell, such as fructolysis and glycation.


Sorbitol occurs naturally in fruits of plants, such as peaches, apples, pears, berries, and prunes. [2] Consumption of these fruits, especially dried prunes, have laxative effects in humans. Sorbitol draws in water to the colon and thereby promotes bowel movements.


Sugar alcohols are also produced semi-artificially from sugars and starch so that they may be used largely as food additives or sugar alternatives. Foods labeled with "no sugar" or "low calorie" contains sugar alcohols in place of sugars. Sugar alcohols (with the exception of the zero-calorie erythritol) provide about 2.4 kilocalories per gram.[2] They are not considered as an essential nutrient -- meaning that even without including them in the diet the individual remains healthy. However, integrating sugar alcohols in the diet may help certain individuals, such as the diabetics, in managing blood glucose levels. Sugar alcohols may be used in place of sucrose (table sugar). Sucrose is a natural sugar produced especially by the plants, sugarcanes and beets. Sucrose is extracted from these plants and then processed as commercial sugar that is used in various food preparations. Sucrose is an essential carbohydrate since it provides both glucose and fructose that are absorbed and fully metabolized by the body. However, they have a high glycemic index (GI). Glucose has a GI of 100 and fructose has 25. Sucrose has a GI of 65. Sugar alcohols have a lower GI (see Table below).[2] A high GI means that it can raise blood glucose levels. A consistently high blood glucose level is implicated in diabetes mellitus and obesity. Apart from having a lower GI, sugar alcohols also give the advantage of not promoting tooth decay. They are not usually fermented or metabolized by oral bacteria, and therefore are not converted into acids or other byproducts that contribute to tooth decay. They are used in the production of toothpastes, lozenges, and medicinal syrups. They are poorly digestible, though. Thus, they could be fermented by the colonic bacteria upon reaching the large intestine. This could lead to diarrhea, flatulence, and abdominal bloating in healthy individuals that ingested large amounts (>20 g) or in sensitive individuals that ingested even a small amount.


Common sugar alcohols

Type Chemical Properties Biological Properties Side effects Industrial uses
Sorbitol

(also called sorbit, glucitol)

Naturally occurs in large amounts in prunes, grapes, cherries, apples, peaches, pears, apricots

Hygroscopic white crystalline powder chemically similar to fructose and mannitol

Sweetness relative to sucrose: 60%

Oral bacteria do not readily ferment it, which makes it tooth-friendly.

Colonic bacteria ferment it into gases and short-chain fatty acids that can be absorbed and provide energy.

Kilocalories per gram: 2.6

Low glycemic index (GI), i.e.GI = 9

Too much sorbitol consumption may lead to diarrhea, flatulence, and abdominal bloating Low-calorie sweetener in food; sweetener in toothpaste, lozenge, medicinal syrups, mouthwash; fat replacer in candies, confectionery, baked goods, chewing gum, chocolate, diet soft drinks; humectant
Maltitol Low hygroscopic powder, made of glucose and sorbitol

Sweetness relative to sucrose: 75%

Oral bacteria do not readily ferment it, which makes it tooth-friendly.

Colonic bacteria ferment it into gases and short-chain fatty acids that can be absorbed and provide energy.

Kilocalories per gram: 2.1

GI= 45

Too much sorbitol consumption may lead to diarrhea, flatulence, and abdominal bloating Low-calorie sweetener; fat replacer or texturizer in candies, ice creams, baked goods, chewing gums, chocolates; humectant
Xylitol

Naturally occurs in small amounts in strawberries, raspberries, yellow plums, cauliflowers, lettuce, spinach

Highly hygroscopic white crystalline powder

Sweetness relative to sucrose: 100%

Oral bacteria do not readily ferment it, which makes it tooth-friendly.

Half of it is absorbed in the small intestine and then converted in the liver to glycogen whereas the other half passes through the colon where colonic bacteria ferment it into gases and short-chain fatty acids that can be absorbed and provide energy.

Kilocalories per gram: 2.4

Low GI, i.e. 12

Too much sorbitol consumption may lead to diarrhea, flatulence, and abdominal bloating Low-calorie sweetener in food; sweetener in toothpaste, lozenge, medicinal syrups, mouthwash
Erythritol

Naturally occurs in low amounts in pears, melons, grapes, mushroom, human body

Low hygroscopic white crystalline substance made up of glucose with added hydroxyl (OH) groups

Sweetness relative to sucrose: 70%

Oral bacteria do not readily ferment it, which makes it tooth-friendly.

Mostly absorbed quickly in the small intestine; excessive erythritol does not stimulate colonic fermentation and thus excreted unchanged in the bowels. Colonic bacteria ferment it into gases and short-chain fatty acids that can be absorbed and provide energy.

Kilocalories per gram: 0.2

Low GI, i.e.0

Too much unabsorbed erythritol may lead to diarrhea, abdominal pain, and headache Zero-calorie carbohydrate sweetener
Isomalt Low hygroscopic white crystalline powder made up of gluco-mannitol and gluco-sorbitol

Sweetness relative to sucrose: 55%

Oral bacteria do not readily ferment it, which makes it tooth-friendly.

A small percentage is absorbed from the small intestine; the rest passes through the colon where colonic bacteria ferment it into gases and short-chain fatty acids that can be absorbed and provide energy.

kilocalories per gram: 2

Low GI, i.e. 9

Too much unabsorbed isomalt in the colon may lead to diarrhea Low-calorie sweetener; bulking agent; anti-caking agent
Glycerol (glycerin)
  • Vegetable glycerin, from vegetable oils, palm kernel oil, coconut oil
  • Animal glycerin as a natural byproduct of animal fats
Highly hygroscopic, thick, translucent, viscous syrup chemically similar to fructose and mannitol

Sweetness relative to sucrose: 75%

Fully absorbed in the small intestines

Kilocalories per gram: 4.3

(GI = ?)

Since it is fully absorbed, nothing passes through the colon Food sweetener; humectant in foods; thickener in foods; emulsifier in pills, toothpaste, mouthwash; lubricant; moisturizer
Lactitol Nonhygroscopic white crystalline powder composed of galactose and sorbitol

Sweetness relative to sucrose: 40%

Oral bacteria do not readily ferment it, which makes it tooth-friendly.

Only 2% is absorbed in the small intestine and the rest passes through the colon where colonic bacteria ferment it into short-chain fatty acids, gases, and lactic acid

Kilocalories per gram: 2

Low GI, i.e.5

Too much lactitol consumption may lead to diarrhea and bloating Low-calorie sweetener in food
Mannitol

Naturally occurs in mushrooms, seaweeds, strawberries, pumpkins celery, onions

Non-hygroscopic white crystalline powder made from fructose and hydrogen

Sweetness relative to sucrose: 60%

Oral bacteria do not readily ferment it, which makes it tooth-friendly.

Poorly absorbed in the small intestine and therefore is fermented into gases and short-chain fatty acids by colonic bacteria when it reaches the colon.

Kilocalories per gram: 1.6

Low GI, i.e. 0

Too much mannitol consumption may lead to diarrhea, flatulence, and abdominal bloating Low-calorie sweetener; anti-caking agent; thickener; emulsifier



Supplementary

Synonyms

  • polyalcohol
  • alditol
  • glycitol



Further reading

See also


Reference

  1. Jedziniak, J. A., Chylack, L.T., Cheng, H.M., Gillis, M.K., Kalustian, A.A., & Tung, W.H. (1981). "The sorbitol pathway in the human lens: aldose reductase and polyol dehydrogenase". Investigative Ophthalmology & Visual Science, 20 (3): 314–26.
  2. Sugar Alcohol: Definition, Side Effects, Use in Diabetes, IBS. (2016, June 4). Retrieved from [Link]



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