Sorbitol

Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes. It is synthesized by sorbitol-6-phosphate dehydrogenase, and converted to fructose by succinate dehydrogenase and sorbitol dehydrogenase. Succinate dehydrogenase is an enzyme complex that participates in the citric acid cycle.

Sweetener
Sorbitol is a sugar substitute. It may be listed under the inactive ingredients listed for some foods and products. Sorbitol is referred to as a nutritive sweetener because it provides dietary energy: 2.6 kilocalories (11 kilojoules) per gram versus the average 4 kilocalories (17 kilojoules) for carbohydrates. It is often used in diet foods (including diet drinks and ice cream), mints, cough syrups, and sugar-free chewing gum.

It also occurs naturally in many stone fruits and berries from trees of the genus Sorbus.

Laxative
Sorbitol can be used as a non-stimulant laxative via an oral suspension or enema. As with other sugar alcohols, gastroitestinal distress may result when food products that contain sorbitol are consumed. Sorbitol exerts its laxative effect by drawing water into the large intestine, thereby stimulating bowel movements. Sorbitol has been determined safe for use by the elderly, although it is not recommended without consultation with a clinician. Sorbitol is found in some dried fruits and may contribute to the laxative effects of prunes.

Medical applications
Sorbitol is used in bacterial culture media to distinguish the pathogenic Escherichia coli O157:H7 from most other strains of E. coli, as it is usually incapable of fermenting sorbitol, but 93% of known E. coli strains are capable of doing so.

Sorbitol, combined with kayexalate, helps the body rid itself of excess potassium ions in a hyperkalaemic state. The kayexalate exchanges sodium ions for potassium ions in the bowel, while sorbitol helps to eliminate it. The FDA has discouraged this combination when in 2010 it issued a warning of increased risk for GI necrosis.

Health care, food, and cosmetic uses
Sorbitol often is used in modern cosmetics as a humectant and thickener. Sorbitol often is used in mouthwash and toothpaste. Some transparent gels can be made only with sorbitol, as it has a refractive index sufficiently high for transparent formulations. It is also used frequently in almost all "sugar free" chewing gum.

Sorbitol is used as a cryoprotectant additive (mixed with sucrose and sodium polyphosphates) in the manufacture of surimi, a highly refined fish paste most commonly produced from Alaska pollock (Theragra chalcogramma). It is also used as a humectant in some cigarettes.

Sorbitol sometimes is used as a sweetener and humectant in cookies and other foods that are not identified as "dietary" items.

Medical importance
Aldose reductase is the first enzyme in the sorbitol-aldose reductase pathway responsible for the reduction of glucose to sorbitol, as well as the reduction of galactose to galactitol. Too much sorbitol trapped in retinal cells, the cells of the lens, and the Schwann cells that myelinate peripheral nerves can damage these cells, leading to retinopathy, cataracts and peripheral neuropathy, respectively. Aldose reductase inhibitors, which are substances that prevent or slow the action of aldose reductase, are currently being investigated as a way to prevent or delay these complications, which frequently occur in the setting of long-term hyperglycemia that accompanies poorly-controlled diabetes. It is thought that these agents may help to prevent the accumulation of intracellular sorbitol that leads to cellular damage in diabetics.

Adverse medical effects
Sorbitol also may aggravate irritable bowel syndrome, and similar gastrointestinal conditions, resulting in severe abdominal pain for those affected, even from small amounts ingested.

Overdose effects
Ingesting large amounts of sorbitol can lead to abdominal pain, gas, and mild to severe diarrhea. Sorbitol ingestion of 20 g per day as sugar-free gum has led to severe diarrhea leading to unintended weight loss of 11 kg in eight months, in a woman originally weighing 52 kg; another patient required hospitalization after habitually consuming 30 g per day.

Compendial status

 * Food Chemical Codex
 * European Pharmacopoeia 6.1
 * British Pharmacopoeia 2009
 * Japanese Pharmacopoeia 15

Miscellaneous uses
A mixture of sorbitol and potassium nitrate has found some success as an amateur solid rocket fuel.

Sorbitol is identified as a potential key chemical intermediate from biomass resources. Complete reduction of sorbitol opens the way to alkanes, such as hexane, which can be used as a biofuel. Sorbitol itself provides much of the hydrogen required for the transformation.


 * 19 C6H14O6 → 13 C6H14 + 36 CO2 + 42 H2O

The above chemical reaction is exothermic; 1.5 moles of sorbitol generate approximately 1 mole of hexane. When hydrogen is co-fed, no carbon dioxide is produced.