Sorbitol (/ˈsɔː(r)bɪtɒl/), less commonly known as glucitol (/ˈɡluːsɪtɒl/), is a sugar alcohol with a sweettaste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alcohol group (−CH2OH). Most sorbitol is made from potato starch, but it is also found in nature, for example in apples, pears, peaches, and prunes.[4] It is converted to fructose by sorbitol-6-phosphate 2-dehydrogenase. Sorbitol is an isomer of mannitol, another sugar alcohol; the two differ only in the orientation of the hydroxyl group on carbon 2.[5] While similar, the two sugar alcohols have very different sources in nature, melting points, and uses.
Sorbitol may be synthesised via a glucose reduction reaction[7] in which the converted aldehyde group is converted into a hydroxyl group. The reaction requires NADH and is catalyzed by aldose reductase. Glucose reduction is the first step of the polyol pathway of glucose metabolism, and is implicated in multiple diabetic complications.
The mechanism involves a tyrosine residue in the active site of aldehyde reductase. The hydrogen atom on NADH is transferred to the electrophilic aldehyde carbon atom; electrons on the aldehyde carbon-oxygen double bond are transferred to the oxygen that abstracts the proton on tyrosine side chain to form the hydroxyl group. The role of aldehyde reductase tyrosine phenol group is to serve as a general acid to provide proton to the reduced aldehyde oxygen on glucose.
Glucose reduction is not the major glucose metabolism pathway in a normal human body, where the glucose level is in the normal range. However, in diabetic patients whose blood glucose level is high, up to 1/3 of their glucose could go through the glucose reduction pathway. This will consume NADH and eventually leads to cell damage.
Sorbitol also may be synthesized through a catalytic hydrogenation of d-glucose to form d-sorbitol.[8][not specific enough to verify] This reaction has a 100% yield of d-sorbitol when d-glucose is reacted with hydrogen in water at 120 degrees Celsius, under 150001.5 Torr, for 1 hour.[citation needed]
Sorbitol is a sugar substitute, and when used in food it has the INS number and E number 420. Sorbitol is about 60% as sweet as sucrose (table sugar).[9]
Sorbitol is referred to as a nutritive sweetener because it provides some dietary energy. It is partly absorbed from the small intestine and metabolized in the body, and partly fermented in the large intestine. The fermentation produces short-chain fatty acidsacetic acid, propionic acid, and butyric acid, which are mostly absorbed and provide energy, but also carbon dioxide, methane, and hydrogen which do not provide energy. Even though the heat of combustion of sorbitol is higher than that of glucose (having two extra hydrogen atoms), the net energy contribution is between 2.5 and 3.4 kilocalories per gram, versus the approximately 4 kilocalories (17 kilojoules) for carbohydrates.[10] It is often used in diet foods (including diet drinks and ice cream), mints, cough syrups, and sugar-free chewing gum.[11] Most bacteria cannot use sorbitol for energy, but it can be slowly fermented in the mouth by Streptococcus mutans, a bacterium that causes tooth decay. In contrast, many other sugar alcohols such as isomalt and xylitol are considered non-acidogenic.[12][13]
As is the case with other sugar alcohols, foods containing sorbitol can cause gastrointestinal distress. Sorbitol can be used as a laxative when taken orally or as an enema.[6] Sorbitol works as a laxative by drawing water into the large intestine, stimulating bowel movements.[6][15] Sorbitol has been determined safe for use by the elderly, although it is not recommended without the advice of a physician.[6][16]
Sorbitol is commonly used orally as a one-time dose of 30–150 millilitres (1.1–5.3 imp fl oz; 1.0–5.1 US fl oz) 70% solution.[6] It may also be used as a one-time rectal enema.[6]
Sorbitol is used in bacterial culture media to distinguish the pathogenic Escherichia coli O157:H7 from most other strains of E. coli, because it is usually unable to ferment sorbitol, unlike 93% of known E. coli strains.[17]
A treatment for hyperkalaemia (elevated blood potassium) uses sorbitol and the ion-exchange resin sodium polystyrene sulfonate (tradename Kayexalate).[18] The resin exchanges sodium ions for potassium ions in the bowel, while sorbitol helps to eliminate it. In 2010, the U.S. FDA issued a warning of increased risk for gastrointestinal necrosis with this combination.[19]
Sorbitol is also used in the manufacture of softgel capsules to store single doses of liquid medicines.[20]
Beyond its use as a sugar substitute in reduced-sugar foods, sorbitol is also used as a humectant in cookies and low-moisture foods like peanut butter and fruit preserves.[24] In baking, it is also valuable because it acts as a plasticizer, and slows down the staling process.[24]
Sorbitol is identified as a potential key chemical intermediate[26] for production of fuels from biomass resources. Carbohydrate fractions in biomass such as cellulose undergo sequential hydrolysis and hydrogenation in the presence of metal catalysts to produce sorbitol.[27] Complete reduction of sorbitol opens the way to alkanes, such as hexane, which can be used as a biofuel. Hydrogen required for this reaction can be produced by aqueous phase catalytic reforming of sorbitol.[28]
^Nicolas, Guillaume G.; Lavoie, Marc C. (January 2011). "[Streptococcus mutans and oral streptococci in dental plaque]". Canadian Journal of Microbiology. 57 (1): 1–20. doi:10.1139/w10-095. ISSN1480-3275. PMID21217792.
^Metzger, Jürgen O. (2006). "Production of Liquid Hydrocarbons from Biomass". Angewandte Chemie International Edition. 45 (5): 696–698. doi:10.1002/anie.200502895. PMID16374789.
^Shrotri, Abhijit; Tanksale, Akshat; Beltramini, Jorge Norberto; Gurav, Hanmant; Chilukuri, Satyanarayana V. (2012). "Conversion of cellulose to polyols over promoted nickel catalysts". Catalysis Science & Technology. 2 (9): 1852–1858. doi:10.1039/C2CY20119D.
^Tanksale, Akshat; Beltramini, Jorge Norberto; Lu, GaoQing Max (2010). "A review of catalytic hydrogen production processes from biomass". Renewable and Sustainable Energy Reviews. 14 (1): 166–182. doi:10.1016/j.rser.2009.08.010.
^Nishikawa, T; Edelstein, D; Du, XL; Yamagishi, S; Matsumura, T; Kaneda, Y; Yorek, MA; Beebe, D; et al. (2000). "Normalizing mitochondrial superoxide production blocks three pathways of hyperglycaemic damage". Nature. 404 (6779): 787–90. Bibcode:2000Natur.404..787N. doi:10.1038/35008121. PMID10783895. S2CID4426750.
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