Sugar alcohols: chemistry, production, health concerns and nutritional importance of mannitol, sorbitol, xylitol, and erythritol

The sugar alcohols commonly found in foods are sorbitol, mannitol, xylitol, erythritol, isomalt, and hydrogenated starch hydrolysates. Sugar alcohols come from plant products such as fruits and berries. Sugar alcohols occur naturally and at one time, mannitol was obtained from natural sources. Today, they are often obtained by hydrogenation of sugars and other techniques. Sugar alcohols do not contribute to tooth decay. Consumption of sugar alcohols may affect blood sugar levels, although less than of sucrose. Sugar alcohols, with the exception of erythritol, may also cause bloating and diarrhea when consumed in excessive amounts. Mannitol and sorbitol are isomers, the only difference being the orientation of the hydroxyl group on carbon 2. Among production methods of mannitol are Industrial synthesis, Biosyntheses, Natural extraction, chemical process, microbial process. Most sorbitol is made from corn syrup, but it is also found in apples, pears, peaches, and prunes. It is converted to fructose by sorbitol-6-phosphate 2-dehydrogenase. Xylitol is a "tooth-friendly", nonfermentable sugar alcohol. It appears to have more dental health benefits than other polyalcohols. The structure of xylitol contains a tridentate ligand, (H-C-OH)3 that can rearrange with polyvalent cations like Ca 2+ . This interaction allows Ca 2+ to be transported through the gut wall barrier and through. Xylitol is produced by hydrogenation of xylose, which converts the sugar (an aldehyde) into a primary alcohol. Another method of producing xylitol is through microbial processes, including fermentative and biocatalytic processes in bacteria, fungi, and yeast cells, which take advantage of the xylose-intermediate fermentations to produce high yield of xylitol. In the body, most erythritol is absorbed into the bloodstream in the small intestine, and then for the most part excreted unchanged in the urine. About 10% enters the colon. Because 90% of erythritol is absorbed before it enters the large intestine, it does not normally cause laxative effects. Chemical and fermentative processes have been introduced for largescale production of erythritol. Erythritol can be synthesized from dialdehyde starch by high-temperature chemical reaction in the presence of a nickel catalyst. International Journal of Advanced Academic Research | Sciences, Technology & Engineering | ISSN: 2488-9849 Vol. 3, Issue 2 (February 2017) Worldwide Knowledge Sharing Platform | www.ijaar. org Page 32 INTRODUCTION Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, comprising a class of polyols. Contrary to what the name may suggest, a sugar alcohol is neither a sugar nor an alcoholic beverage. They are white, water-soluble solids that can occur naturally or be produced industrially from sugars. They 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 intensity artificial sweeteners to counter the low sweetness. Xylitol is perhaps the most popular sugar alcohol due to its similarity to sucrose in visual appearance and sweetness. The sugar alcohols commonly found in foods are sorbitol, mannitol, xylitol, isomalt, and hydrogenated starch hydrolysates. Sugar alcohols come from plant products such as fruits and berries. The carbohydrate in these plant products is altered through a chemical process. The carbohydrate in these plant products is altered through a chemical process. These sugar substitutes provide somewhat fewer calories than table sugar (sucrose), mainly because they are not well absorbed and may even have a small laxative effect. Many so-called "dietetic" foods that are labeled "sugar free" or "no sugar added" in fact contain sugar alcohols. People with diabetes mistakenly think that foods labeled as "sugar free" or "no sugar added" will have no effect on their blood glucose. Foods containing these sugar alcohols need to have their calorie and carbohydrate contents accounted for in your overall meal plan, as it is carbohydrate that raises blood glucose levels. Since many people typically overeat "sugar free" or "no sugar added" foods, their blood glucose may be significantly elevated. Sugar alcohols have the general formula HOCH2(CHOH)nCH2OH. In contrast, sugars have two fewer hydrogen atoms, for example HOCH2(CHOH)nCHO or HOCH2(CHOH)n−1C(O)CH2OH. The sugar alcohols differ in chain length. Most have fiveor 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) 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. sorbitol can be dehydrated to isosorbide. Sugar alcohols occur naturally and at one time, mannitol was obtained from natural sources. Today, they are often obtained by hydrogenation of sugars, using Raney nickel catalysts. The conversion of glucose and mannose to sorbitol and mannitol is given: 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 annually. Xylitol and lacticol are obtained similarly. Erythritol on the other hand is obtained by fermentation of glucose and sucrose.