Xylitol is a sugar alcohol used as a sweetener. The name derives from Ancient Greek: ?????, xyl[on], "wood" + suffix -itol, used to denote sugar alcohols. Xylitol is categorized as a polyalcohol or sugar alcohol (specifically an alditol). It has the formula CH2OH(CHOH)3CH2OH. It is a colorless or white solid that is soluble in water. The compound has attracted popular attention because evidence suggests that it reduces the incidence of cavities. Small amounts of xylitol occur naturally in some fruits.
Video Xylitol
Structure, production, occurrence
Unlike most sugar alcohols, xylitol is an achiral. Most other isomers of pentane-1,2,3,4,5-pentol are chiral, but xylitol has a plane of symmetry.
Industrial production starts from xylan, a hemicellulose, which is extracted from hardwoods or corncobs. These polymers can be hydrolyzed into xylose, which are catalytically hydrogenated into xylitol. The conversion changes the sugar (xylose, an aldehyde) into a primary alcohol (xylitol).
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.
Maps Xylitol
Food properties
One gram of xylitol contains 2.43 kilocalories (10.2 kilojoules), which is about 63% as much as one gram of sugar, which has 3.87 kcal (16.2 kJ). Xylitol has virtually no aftertaste, and is advertised as "safe for diabetics and individuals with hyperglycemia." Xylitol's lower effect on blood sugar is a function of its glycemic index (GI); xylitol's GI is 7, compared to 100 for glucose.
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.
In some individuals, xylitol consumption is limited by gastrointestinal issues, including flatulence, osmotic diarrhea, and irritable bowel syndrome. However, for many, the side effects are negligible. In one study, subjects consumed an average of 1.5 kg (3.3 lb) of xylitol per month, with a maximum daily intake of over 400 g (14 oz) without any negative effects.
Health aspects
Dental care
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 that can coordinate with polyvalent cations such as Ca2+. This interaction allows Ca2+ to be transported through the gut wall barrier and through saliva which may allow enamel to remineralize before dental cavities form.
Early studies from Finland in the 1970s found, compared with chewing sucrose-sweetened 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 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 6 grams of xylitol per day, in three to five chewing episodes, is thought to be needed for dental efficacy. A source of xylitol that releases it slowly, and a one- to three-minute initial pulse are thought to improve the dental effect.
Xylitol also inhibits the growth of Streptococcus pneumoniae, as well as the attachment of Haemophilus influenzae on the nasopharyngeal cells.
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-cavity 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 cavities, a further examination of data from this study revealed a significant reduction in the incidence of root caries in the group that received xylitol.
A review of xylitol's effects on dental cavities concludes that the body of evidence is of low to very low quality and is insufficient to determine whether any other xylitol-containing products can prevent cavities in infants, older children, or adults.
Diabetes
Xylitol has negligible effects on blood sugar and insulin. None of the harmful effects of normal sugars apply to xylitol. The glycemic index (a measure of how quickly foods raise blood sugar) is only 7, compared to sucrose (table sugar), which has a glycemic index of 65. It can also be considered a weight loss friendly sweetener, since it contains 40% fewer calories than sugar.
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.
A study in laboratory rats using an induced model of diabetes found favorable biomarker outcomes for rats given xylitol compared to control rats.
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.
Ear infection
Xylitol chewing gum appears to decrease rates of acute otitis media in healthy children going to daycare by 25%, but evidence of efficacy in children with respiratory infection or who are otitis-prone is inconclusive. 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.
Osteoporosis
A feed containing xylitol increased bone volume in rat studies conducted in 2001 and 2011, these results have generated interest in the sugar that would examine if it could be a human treatment for osteoporosis.
Toxicity
In humans
Xylitol has no known toxicity in humans; however, some report heart palpitations after consuming it. In one study, participants consumed 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, xylitol has a laxative effect because sugar alcohols are not fully broken down during digestion; however, the effect varies from person to person. In one study of 13 children, four experienced diarrhea from xylitol's laxative effect when they ate more than 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 of xylitol in excess of one's "laxation threshold" (the amount of sweetener that can be consumed before abdominal discomfort occurs) can result in temporary gastrointestinal side effects, such as bloating, flatulence, and diarrhea. Adaptation (that is, 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 mannitol and sorbitol.
In dogs
Xylitol is often fatal 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 eaten 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 to 1000 mg/kg bodyweight) has been implicated in liver failure in dogs, which can be fatal.
In wild birds
Thirty Cape sugarbirds died within 30 minutes of drinking a solution made with xylitol from a feeder in a garden in Hermanus, South Africa. It is suspected that it triggered a massive insulin release, causing an irreversible drop in blood sugar.
See also
References
Source of the article : Wikipedia
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