Sugar alcohols (also calledpolyhydric alcohols,polyalcohols,alditols orglycitols) areorganic compounds, typicallyderived fromsugars, containing onehydroxyl group(−OH) attached to each carbon atom. They are white, water-soluble solids that can occur naturally or be produced industrially byhydrogenating sugars. Since they contain multiple(−OH) groups, they are classified aspolyols.
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), often in combination with high-intensityartificial sweeteners, in order to offset their low sweetness.Xylitol andsorbitol are popular sugar alcohols in commercial foods.[1]
Sugar alcohols are synthesised by most microorganisms and plants, with roles in maintaining cellular water balance and responding to stresses, such as water deficiency or low temperature.[2]
Simple sugar alcohols have the general formulaHOCH2(CHOH)nCH2OH. In contrast, sugars have two fewer hydrogen atoms, for example,HOCH2(CHOH)nCHO orHOCH2(CHOH)n−1C(O)CH2OH. Like their parent sugars, sugar alcohols exist in diverse chain length. Most have five- or six-carbon chains, because they are derived respectively frompentoses (five-carbon sugars) andhexoses (six-carbon sugars), which are the more common sugars. They have one −OH group attached to each carbon. They are further differentiated by the relative orientation (stereochemistry) of these −OH groups. Unlike sugars, which tend to exist as rings, sugar alcohols do not, although they can be dehydrated to give cyclic ethers (e.g.sorbitan can be dehydrated toisosorbide).
Some disaccharides can behydrogenated to give useful disaccharide alcohols with retention of the acetal linkage. Commercial products includelactitol,isomalt, andmaltitol.[3]
Sugar alcohols can be, and often are, produced fromrenewable resources. Particular feedstocks arestarch,cellulose andhemicellulose; the main conversion technologies useH2 as the reagent:hydrogenolysis,i.e. thecleavage ofC−O single bonds, convertingpolymers to smaller molecules, andhydrogenation ofC=O double bonds, converting sugars tosugar alcohols.[4]
Mannitol is no longer obtained from natural sources; currently, sorbitol and mannitol are obtained byhydrogenation of sugars, usingRaney nickel catalysts.[1] The conversion of glucose and mannose to sorbitol and mannitol is given as
Erythritol is obtained by thefermentation of glucose andsucrose.
Bothdisaccharides andmonosaccharides can form sugar alcohols; however, sugar alcohols derived from disaccharides (e.g. maltitol and lactitol) are not entirelyhydrogenated because only onealdehyde group is available for reduction.
This table presents the relative sweetness andfood energy of the most widely used sugar alcohols. Despite the variance in food energy content of sugar alcohols, theEuropean Union's labeling requirements assign a blanket value of 2.4 kcal/g to all sugar alcohols.
| Name | Relative sweetness (%)a | Food energy (kcal/g)b | Relative food energy (%)b | Glycemic indexc | Maximum non-laxative dose (g/kg body weight) | Dental acidityd | |
|---|---|---|---|---|---|---|---|
| Arabitol | 70 | 0.2 | 5.0 | ? | ? | ? | |
| Erythritol | 60–80 | 0.21 | 5.3 | 0 | 0.66–1.0+ | None | |
| Glycerol | 60 | 4.3 | 108 | 3 | ? | ? | |
| HSHsTooltip Hydrogenated starch hydrolysates | 40–90 | 3.0 | 75 | 35 | ? | ? | |
| Isomalt | 45–65 | 2.0 | 50 | 2–9 | 0.3 | ? | |
| Lactitol | 30–40 | 2.0 | 50 | 5–6 | 0.34 | Minor | |
| Maltitol | 90 | 2.1 | 53 | 35–52 | 0.3 | Minor | |
| Mannitol | 40–70 | 1.6 | 40 | 0 | 0.3 | Minor | |
| Sorbitol | 40–70 | 2.6 | 65 | 9 | 0.17–0.24 | Minor | |
| Xylitol | 100 | 2.4 | 60 | 12–13 | 0.3–0.42 | None | |
| Footnotes:a =Sucrose is 100%.b =Carbohydrates, including sugars like glucose, sucrose, andfructose, are ~4.0 kcal/g and 100%.c =Glucose is 100 and sucrose is 60–68.d = Sugars, like glucose, sucrose, andfructose, are high.References:[5][6][7][8][9][10] | |||||||
As a group, sugar alcohols are not as sweet as sucrose, and they have slightly lessfood energy than sucrose. Their flavor is similar to sucrose, and they can be used to mask the unpleasantaftertastes of some high-intensitysweeteners.
Sugar alcohols are not metabolized by oral bacteria, and so they do not contribute totooth decay.[11][12] They do not brown orcaramelize 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-freehard candy orchewing gum. This happens, for example, with thecrystalline phase of sorbitol, erythritol, xylitol, mannitol,lactitol andmaltitol. Thecooling sensation is due to the dissolution of the sugar alcohol being an endothermic (heat-absorbing) reaction,[1] one with a strongheat of solution.[13]
Sugar alcohols are usually incompletely absorbed into the blood stream from thesmall intestine which generally results in a smaller change inblood glucose than "regular" sugar (sucrose). This property makes them popular sweeteners amongdiabetics and people onlow-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.[1][14]
Sugar alcohols do not contribute totooth decay; in fact, xylitol deters tooth decay.[11][12]
Sugar alcohols are absorbed at 50% of the rate of sugars, resulting in less of an effect onblood sugar levels as measured by comparing their effect to sucrose using theglycemic index.[15][16]
Like many other incompletely digestible substances, overconsumption of sugar alcohols can lead tobloating,diarrhea andflatulence 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.[14]
