What is Sorbitol?

The sugar alcohol which is found in most of the plants and fruits is known as sorbitol. It has diuretic, and laxative property. When sorbitol remains unabsorbed by the body it will lead to water retention in large intestine by the process of osmotic pressure resulting in peristaltic movement of the intestine and performing its diuretic and laxative activity. The important property of sorbitol is it is used as an alternative for sucrose as it has one third amount of less calories when compared with sucrose and also $60\%$ of the sweetening property of sucrose. It has the chemical formula${\text{C}}_{\text{6}}\text{}{\text{H}}_{\text{14}}\text{}{\text{O}}_{\text{6}}$. Sorbitol is a water soluble odorless and colorless solid.

Stability of Sorbitol

Sorbitol is generally inert chemically but most reagents are compatible. In the lack of catalyst and cold, diluted acids and alkalis it really is stable in air. At high temperatures or in the existence of amines, sorbitol does not blacken or disintegrate. It is non-volatile, non - flammable, and non-corrosive. Even though sorbitol is immune to ferment by numerous microorganisms, sorbitol solutions should include a preservative. Sorbitol solutions shall be handled in bottles, ceramic, aluminum and stainless steel tubes.

Structure of Sorbitol

Sorbitol is a slowly metabolizing sugar alcohol from the body. The aldehyde group can be reduced to hydroxyl group through glucose reduction giving rise to sorbitol. The apple, pear, peach and plum are plants mostly associated with occurrence of sorbitol. It is synthesized by sorbitol-6-phosphate dehydrogenase, and transformed by succinate dehydrogenase and sorbitol dehydrogenase into fructose. This is usually found in diet drinks, cough syrups as well as chewing gums without sugar. It may be employed as a non-starters through oral suspension or laxative and may inadvertently induce GI discomfort when swallowing food with an excess of sorbitol, much as other sugar alcohols other than erysthritol. Sorbitol is also another isomer of the compound known as mannitol in sugar. The only distinction among mannitol and sorbitol is the position in the 2nd carbon hydroxyl group. NADH is a very critical element of the reaction because the protons are donated to reduce it. The two sugar alcohols have, however, very specific sources, melting point as well as applications.

Mannitol

Mannitol is a sugar alcohol beneficial as a drug as well as a sweetener. We should use mannitol as a diabetic food because it is slowly absorbed by the intestine. We will use mannitol as a drug to reduce intraocular pressure and the intracranial pressure. It can be given in the form of a medical injection. The reduction of mannose sugar enables one to produce mannitol. The commercial mannitol production is, furthermore, by fructose hydrogenation. In addition, certain species generate mannitol as source of energy, such as bacteria, fungi, algae, lichens and so on. Moreover, mannitol can be extracted specifically from its plant sources such as seaweed.

Difference between Sorbitol and Mannitol

Sorbitol and mannitol are termed as structural isomers to each other. The only difference between a sorbitol and mannitol is the position of the hydroxyl group present at the second carbon atom. In Fischer projection the sorbitol hydroxyl atom at the second carbon atom projects out of the plane whereas for mannitol it projects behind the plane. Sorbitol is commonly found in fruits such as peaches and apple while mannitol is produced by few organisms as an energy source such as few bacteria and fungi. Other important distinction between sorbitol and mannitol is their melting points sorbitol has a melting point of around 201-208 degrees Fahrenheit on the other hand mannitol has a melting point of around 327-336 degrees Fahrenheit.

Similarities Between Sorbitol and Mannitol

• The two groups of sugar alcohols sorbitol and mannitol are polyols.
• They are used as sweeteners for alternative purposes. Also, they are nutritious and found in some fruits as well as vegetables.

• Both sorbitol and mannitol are odorless powders of white color.
• Hydrogenation of saccharides will give rise to both these compounds.
• Both sorbitol and mannitol have Fructose as common parent molecule.
• Ethyl alcohol is not found in both thus no intoxicating properties are observed in either of these compounds.

Applications of Sorbitol

Sorbitol has various applications as follows:

Sweetening agent

Sorbitol is a replacement for sugar. It can appear in certain foodstuffs under inert components. The sweetness of Sorbitol is around 60 percent that of table sugar. Nutritious sweetener is related to as Sorbitol, because it contains dietary energy: $2.6\text{ kg }\left(11\text{ kilojules}\right)$per gram in comparison to $4\text{ kg }\left(17\text{ kilojoules}\right)$of carbohydrates. Sorbitol supplies a dietary energy. It is also found in diet foods, minting, cough sips, and sugar-free chewing gum (including food beverages and ice cream). In several stone fruits and berries of the Sorbus genus, it is also naturally present.

Laxative

Sorbitol can be used through oral application or injection as a laxative. Gastrointestinal pain may occur, similar to other sugar alcohols, in consuming foods containing sorbitol. Through pumping water in the large intestine, it stimulates bowel motions and imposes its laxative impact

Side effects of sorbitol

The adverse consequences of sorbitol use are subtle; gastrointestinal disorders are the major health issue since sorbitol is not fully absorbed in the intestine. Sorbitol is absorbed by the small intestine in minimal quantities which eventually become fructose. Diarrhea may be caused by the excessive concentration of the residual sorbitol. Unnecessarily high sorbitol use can cause complexity of the gastrointestinal tract, such as flatulence, indigestion, tightness and others. The ingestion of sorbitol can cause severe complications in persons particularly susceptible to laxative symptoms.

Synthesis of Sorbitol using Maize Starch

By sequential hydrogenation as well as hydrolysis with a nickel catalyst and pressure of around 100 atmospheres, sorbitol can be manufactured out of maize starch. The involvement of such metal salts, for example magnesium, nickel including calcium chloride, increases the transformation performance which is achieved in two stages.

• Maize starch transformation liquid to Glucose/Dextrose through hydrolysis.
• Dextrose/liquid glucose transformation into sorbitol under intense pressure upon hydrogenation.

Common Mistakes

Common mistake the student can do while drawing Fischer projection structure of sorbitol and mannitol. Students should be careful while drawing the bonds for their structures.

Practice Problems

Draw the structure of sorbitol and mannitol

Solution: First image is of sorbitol and the next one is mannitol.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for,

• B.Sc. in Chemistry, Biotechnology, Biochemistry and Biology
• M.Sc. in Chemistry, Biotechnology, Biochemistry and Biology