Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

s, typically derived from

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...

s, containing one hydroxyl group (–OH) attached to each carbon atom. They are white, water-soluble solids that can occur naturally or be produced industrially by

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate org ...

of sugars. Since they contain multiple –OH groups, they are classified as polyols. Sugar alcohols are used widely in the food industry as thickeners and sweeteners. In commercial foodstuffs, sugar alcohols are commonly used in place of table sugar (

sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...

), often in combination with high-intensity artificial sweeteners, in order to offset their low sweetness. Xylitol and

sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alcoh ...

are popular sugar alcohols in commercial foods.

Chemical structure

Sugar alcohols have the general formula HOCH₂(CHOH)_''n''CH₂OH. In contrast, sugars have two fewer hydrogen atoms, for example HOCH₂(CHOH)_''n''CHO or HOCH₂(CHOH)_''n''−1C(O)CH₂OH. The sugar alcohols differ in chain length. Most have five- or six-carbon chains, because they are derived from pentoses (five-carbon sugars) and hexoses (six-carbon sugars), respectively. They have one –OH group attached to each carbon. They are further differentiated by the relative orientation (

stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereois ...

) of these –OH groups. Unlike sugars, which tend to exist as rings, sugar alcohols do not. They can, however, be dehydrated to give cyclic ethers; e.g.

can be dehydrated to

isosorbide Isosorbide is a bicyclic chemical compound from the group of diols and the oxygen-containing heterocycles, containing two fused furan rings. The starting material for isosorbide is D-sorbitol, which is obtained by catalytic hydrogenation of ...

Production

Sorbitol and mannitol

Mannitol is no longer obtained from natural sources; currently, sorbitol and mannitol are obtained by

of sugars, using Raney nickel catalysts. The conversion of glucose and mannose to sorbitol and mannitol is given as: :HOCH₂CH(OH)CH(OH)CH(OH)CH(OH)CHO + H₂ → HOCH₂CH(OH)CH(OH)CH(OH)CH(OH)CHHOH More than a million tons of sorbitol are produced in this way every year. Xylitol and lactitol are obtained similarly.

Erythritol

Erythritol is obtained by the fermentation of glucose and

Health effects

Sugar alcohols do not contribute to tooth decay; on the contrary, xylitol is a deterrent to tooth decay. Sugar alcohols are absorbed at 50% of the rate of sugars, resulting in less of an effect on blood sugar levels as measured by comparing their effect to sucrose using the glycemic index. The unabsorbed sugar alcohols may cause bloating and

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin ...

if consumed in sufficient amounts.

Common sugar alcohols

* Ethylene glycol (2-carbon) * Glycerol (3-carbon) * Erythritol (4-carbon) * Threitol (4-carbon) * Arabitol (5-carbon) * Xylitol (5-carbon) * Ribitol (5-carbon) * Mannitol (6-carbon) *

Sorbitol Sorbitol (), less commonly known as glucitol (), is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alcoh ...

(6-carbon) *

Galactitol Galactitol (dulcitol) is a sugar alcohol, the reduction product of galactose. It has a slightly sweet taste. In people with galactokinase deficiency, a form of galactosemia, excess dulcitol forms in the lens of the eye leading to cataracts. Gala ...

(6-carbon) * Fucitol (6-carbon) *

Iditol Iditol is a sugar alcohol which accumulates in galactokinase deficiency. See also *Idose *Aldose reductase *L-iditol 2-dehydrogenase External links

* Sugar alcohols {{biochemistry-stub ...

(6-carbon) *

Inositol Inositol, or more precisely ''myo''-inositol, is a carbocyclic sugar that is abundant in the brain and other mammalian tissues; it mediates cell signal transduction in response to a variety of hormones, neurotransmitters, and growth factors and ...

(6-carbon; a cyclic sugar alcohol) *

Volemitol Volemitol is a naturally occurring seven-carbon sugar alcohol. It is a substance widely distributed in plants, red algae, fungi, mosses, and lichens. It was also found in lipopolysaccharides from '' E. coli''. In certain higher plants, such as ...

(7-carbon) * Isomalt (12-carbon) * Maltitol (12-carbon) * Lactitol (12-carbon) *Maltotriitol (18-carbon) *Maltotetraitol (24-carbon) *Polyglycitol Both disaccharides and

monosaccharide Monosaccharides (from Greek ''monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built. They are usually colorless, water-solub ...

s can form sugar alcohols; however, sugar alcohols derived from disaccharides (e.g. maltitol and lactitol) are not entirely hydrogenated because only one aldehyde group is available for reduction.

Sugar alcohols as food additives

This table presents the relative sweetness and food energy of the most widely used sugar alcohols. Despite the variance in food energy content of sugar alcohols, EU labeling requirements assign a blanket value of 2.4 kcal/g to all sugar alcohols.

Characteristics

As a group, sugar alcohols are not as sweet as sucrose, and they have slightly less food energy than sucrose. Their flavor is similar to sucrose, and they can be used to mask the unpleasant aftertastes of some high-intensity sweeteners. Sugar alcohols are not metabolized by oral bacteria, and so they do not contribute to tooth decay. They do not brown or caramelize when heated. In addition to their sweetness, some sugar alcohols can produce a noticeable cooling sensation in the mouth when highly concentrated, for instance in sugar-free hard candy or chewing gum. This happens, for example, with the crystalline phase of sorbitol, erythritol, xylitol, mannitol, lactitol and maltitol. The cooling sensation is due to the dissolution of the sugar alcohol being an endothermic (heat-absorbing) reaction, one with a strong heat of solution.

Absorption from the small intestine

Sugar alcohols are usually incompletely absorbed into the blood stream from the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...

which generally results in a smaller change in blood glucose than "regular" sugar (sucrose). This property makes them popular sweeteners among diabetics and people on low-carbohydrate diets. As an exception, erythritol is actually absorbed in the small intestine and excreted unchanged through urine, so it contributes no calories even though it is rather sweet.

Side effects

Like many other incompletely digestible substances, overconsumption of sugar alcohols can lead to bloating,

and flatulence because they are not fully absorbed in the small intestine. Some individuals experience such symptoms even in a single-serving quantity. With continued use, most people develop a degree of tolerance to sugar alcohols and no longer experience these symptoms.

References

{{Alcohols Sugar substitutes fr:Polyol