|Molar mass||152.15 g·mol−1|
|Melting point||92 to 96 °C (198 to 205 °F; 365 to 369 K)|
|Boiling point||345.39 °C (653.70 °F; 618.54 K) Predicted value using Adapted Stein & Brown method|
|~ 0.1 g/mL|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Xylitol // is a sugar alcohol used as a sweetener. The name derives from Greek: ξύλον, xyl[on], "wood" + suffix -itol, used to denote sugar alcohols. Xylitol is categorized as a polyalcohol or sugar alcohol (alditol). It has the formula CH2OH(CHOH)3CH2OH and is an achiral isomer of pentane-1,2,3,4,5-pentol. Xylitol is roughly as sweet as sucrose (table sugar), with 33% fewer calories. Unlike other natural or synthetic sweeteners, xylitol is actively beneficial for dental health by reducing caries (cavities) to a third in regular use and helpful to remineralization. Multiple studies utilizing electron microscopy have indicated that xylitol is effective in inducing remineralization of deeper layers of demineralized enamel. Fair evidence was found that xylitol (as chewing gum, lozenges, nasal spray, etc.) reduced the incidence of acute middle ear infection in healthy children.
Xylitol is naturally found in low concentrations in the fibers of many fruits and vegetables, and can be extracted from various berries, oats, and mushrooms, as well as fibrous material such as corn husks and sugar cane bagasse, and birch. However, industrial production starts from xylan (a hemicellulose) extracted from hardwoods or corncobs, which is hydrolyzed into xylose and catalytically hydrogenated into xylitol. A study in rats found that xylitol had reduced or nonexistent side effects compared to other artificial sweeteners, and lower caloric value and cariogenicity than sucrose.
Xylitol was discovered almost simultaneously by German and French chemists in the late 19th century, and was first popularized in Europe as a safe sweetener that would not affect insulin levels of people with diabetes. Xylitol is produced by hydrogenation of xylose, which converts the sugar (an aldehyde) into a primary alcohol. It can also be extracted from natural sources, and is often harvested by tapping birch trees to produce birch sap. Another method of producing xylitol is through microbial processes, including fermentative and biocatalytic processes in bacteria, fungi, and yeast cells, that take advantage of the xylose-intermediate fermentations to produce high yield of xylitol. Common yeast cells used in effectly fermenting and producing xylitol are Candida tropicalis and Candida guilliermondii. Its dental significance was researched in Finland in the early 1970s. There, scientists at University of Turku demonstrated dental benefits in what became known as the "Turku sugar studies".
One gram of xylitol contains 2.4 kilocalories (kcal), as compared to one gram of sugar, which has 3.87 kcal. Xylitol has virtually no aftertaste, and is advertised as "safe for diabetics and individuals with hyperglycemia." This tolerance is attributed to the lower effect of xylitol on a person's blood sugar, compared to that of regular sugars as it has an extremely low glycemic index of 7 (glucose has a GI of 100). Xylitol has no known toxicity or carcinogenicity, and is considered safe by the U.S. FDA
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 Ca2+. This interaction allows Ca2+ to be transported through the gut wall barrier and through saliva may remineralize enamel before dental cavities form.
Early studies from Finland in the 1970s found compared to chewing sucrose-flavored gum, xylitol resulted in nearly two fewer cavities or missing teeth. Cavity-causing bacteria prefer six-carbon sugars or disaccharides, while xylitol is non-fermentable and cannot be used as an energy source - while still being taken up into the cell (due to similar shape) and leaving no room for the six-carbon sugars, interfering with bacterial growth and reproduction. The harmful micro-organisms are starved in the presence of xylitol, allowing the mouth to remineralize damaged teeth with less interruption. This same property renders it unsuitable for making bread as it interferes with the ability of yeast to digest sugars. At least six grams of xylitol per day is thought to be needed for dental efficacy.
The perception of sweetness obtained from consuming xylitol causes the secretion of saliva which acts as a buffer against the acidic environment created by the microorganisms in dental plaque. Increase in salivation can raise the falling pH to a neutral range within few minutes of xylitol consumption.
However, despite these promising conjectures two systematic reviews of clinical trials could not find conclusive evidence that xylitol was indeed superior to other polyols such as sorbitol or equal to that of topical fluoride in its anti-caries effect.
In the 33-month Xylitol for Adult Caries Trial, participants were given lozenges of either five grams of xylitol or a sucralose-sweetened placebo. While this study initially found no statistically significant reduction in 33-month caries increment among adults at an elevated risk of developing caries, a further examination of data from this study revealed a significant reduction in the incidence of root caries in the group that received xylitol.
Xylitol is categorized by the U.S. Food and Drug Administration as a food additive. Like other sugar alcohol-sweetened products, xylitol-sweetened products are allowed to be labeled with the claim that they do not promote dental cavities.
Possessing approximately 33% fewer calories, xylitol is a lower-calorie alternative to table sugar. Absorbed more slowly than sugar, it does not contribute to high blood sugar levels or the resulting hyperglycemia caused by insufficient insulin response. This characteristic has also proven beneficial for people suffering from metabolic syndrome, a common disorder that includes insulin resistance, hypertension, hypercholesterolemia, and an increased risk for blood clots. Xylitol is used as a sweetener in medicines, chewing gum and pastilles.
Source of energy
In the human gut xylitol is not absorbed as well as glucose or fructose; the unabsorbed xylitol acts as a dietary soluble fiber in helping to maintain certain aspects of gut function. Bacterial fermentation, mainly in the large gut, partly converts xylitol to short-chain fatty acids that the gut can absorb as fuel for energy production in oxidative metabolic pathways. Xylitol also is useful in recovery after heavy exercise because the human body converts absorbed xylitol to glucose 6-phosphate and glycogen. The conversion is however slow, so that the xylitol amounts to a low-GI source of energy.
Xylitol chewing gum appears to decrease rates of acute otitis media in children going to daycare by 25%. Xylitol nasal sprays have also been shown to decrease incidence of acute otitis media as well as being a very effective way of both assisting and stimulating the body's own natural nasopharyngeal washing, and reducing both bacterial colonization and allergenic pollution, with their accompanying problems.
Xylitol has no known toxicity in humans. In one study, the participants consumed a diet containing a monthly average of 1.5 kg of xylitol with a maximum daily intake of 430 g with no apparent ill effects. Like most sugar alcohols, it has a laxative effect because sugar alcohols are not fully broken down during digestion; albeit one-tenth the strength of sorbitol.[clarification needed] The effect depends upon the individual. In one study of 13 children, four experienced diarrhea when consuming over 65 grams per day. Studies have reported that adaptation occurs after several weeks of consumption.
As with other sugar alcohols, with the exception of erythritol, consumption in excess of one's laxation threshold (the amount of sweetener that can be consumed before abdominal discomfort sets in) can result in temporary gastrointestinal side effects, such as bloating, flatulence, and diarrhea. Adaptation, an increase of the laxation threshold, occurs with regular intake. Xylitol has a lower laxation threshold than some sugar alcohols, but is more easily tolerated than others such as mannitol and sorbitol.
Xylitol toxicity in dogs
Xylitol is well established as a life-threatening toxin to dogs. According to the ASPCA Animal Poison Control Center, the number of cases of xylitol toxicosis in dogs has significantly increased since the first reports in 2002. Dogs that have ingested foods containing xylitol (greater than 100 milligrams of xylitol consumed per kilogram of bodyweight) have presented with low blood sugar (hypoglycemia), which can be life-threatening. Low blood sugar can result in a loss of coordination, depression, collapse and seizures in as little as 30 minutes. Intake of doses of xylitol (greater than 500 – 1000 mg/kg bwt) has been implicated in liver failure in dogs, which can be fatal. Possible cause of hypoglycemia experienced by dogs is the fact that the xylitol in gum is released more slowly and absorbed over longer period than when it is consumed as a pure form.
Notes and references
- Material safety data sheet for xylitol from Fisher Scientific. Retrieved on 2014-11-02.
- "Xylitol". Chemspider. Retrieved 13 May 2015.
- Wrolstad, Ronald E. (2012). Food Carbohydrate Chemistry. John Wiley & Sons. p. 176. ISBN 9780813826653. Retrieved October 20, 2012.
Xylitol contains asymmetric carbon atoms, but it is not chiral because the molecule as a whole is symmetrical.
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