Xylitol

Template:Chembox Xylitol is a chemical compound with the formula Template:Chem, or HO(CH₂)(CHOH)₃(CH₂)OH; specifically, one particular stereoisomer with that structural formula. It is a colorless or white crystalline solid. It is classified as a polyalcohol and a sugar alcohol, specifically an alditol. Of the common sugar alcohols, only sorbitol is more soluble in water.

The name derives from Template:Langx, xyl[on] 'wood', with the suffix -itol used to denote it being a sugar alcohol.

Xylitol is used as a food additive and sugar substitute. Its European Union code number is E967.<ref name=EAPP-Food-legtn> {{#invoke:citation/CS1|citation |CitationClass=web }} </ref> Replacing sugar with xylitol in food products may promote better dental health, but evidence is lacking on whether xylitol itself prevents dental cavities.<ref name=Riley-etal-2015> Template:Cite journal</ref><ref>Template:Cite journal Template:Open access </ref> In the United States, xylitol is used as a common sugar substitute, and is considered to be safe for humans.<ref name="fda">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Xylitol can be toxic to dogs.<ref name="dogs-fda">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

History

Emil Fischer, a German chemist, and his assistant Rudolf Stahel isolated a new compound from beech wood chips in September 1890 and named it {{#invoke:Lang|lang}}, after the Greek word for wood. The following year, the French chemist M. G. Bertrand isolated xylitol syrup by processing wheat and oat straw.<ref name="pmid10890712">Template:Cite journal</ref> Sugar rationing during World War II led to an interest in sugar substitutes. Interest in xylitol and other polyols became intense, leading to their characterization and manufacturing methods.<ref name=Ur-Rehman-etal-2015/><ref name=Hicks-2010> Template:Cite magazine</ref>

Structure, production, commerce

Xylitol is one of three 5-carbon sugar alcohols. The others are arabitol and ribitol. These three compounds differ in the stereochemistry of the three secondary alcohol groups. {{#invoke:Gallery|gallery}}

Xylitol occurs naturally in small amounts in plums, strawberries, cauliflower, and pumpkin; humans and many other animals make trace amounts during metabolism of carbohydrates.<ref name=Ur-Rehman-etal-2015/> Unlike most sugar alcohols, xylitol is achiral.<ref name=Wrolstad-2012> Template:Cite book </ref> Most other isomers of pentane-1,2,3,4,5-pentol are chiral, but xylitol has a plane of symmetry.

Industrial production starts with lignocellulosic biomass from which xylan is extracted; raw biomass materials include hardwoods, softwoods, and agricultural waste from processing maize, wheat, or rice. The mixture is hydrolyzed with acid to give xylose. The xylose is purified by chromatography. Purified xylose is catalytically hydrogenated into xylitol using a Raney nickel catalyst.<ref name=Ullmann>Template:Cite book</ref> The conversion changes the sugar (xylose, an aldehyde) into the primary alcohol, xylitol.<ref name=Ur-Rehman-etal-2015/>

Xylitol can also be obtained by industrial fermentation, but this methodology is not as economical as the acid hydrolysis/chromatography route described above. Fermentation is effected by bacteria, fungi, or yeast, especially Candida tropicalis.<ref name=Ur-Rehman-etal-2015/><ref name=Jain-Mulay-2014> Template:Cite journal </ref> According to the US Department of Energy, xylitol production by fermentation from discarded biomass is one of the most valuable renewable chemicals for commerce, forecast to be a US $1.41 billion industry by 2025.<ref name=Felipe-H-P-etal-2019> Template:Cite journal</ref>

Uses

Xylitol is used as a sugar substitute in such manufactured products as drugs, dietary supplements, confections, toothpaste, and chewing gum, but is not a common household sweetener.<ref name=Riley-etal-2015/><ref name=fda/><ref name=Drugs-2018> {{#invoke:citation/CS1|citation |CitationClass=web }} </ref> Xylitol has negligible effects on blood sugar because its assimilation and metabolism are independent of insulin.<ref name=Drugs-2018/> It is approved as a food additive and sugar substitute in the United States.<ref name=fda/>

Xylitol is also found as an additive to saline solution for nasal irrigation and has been reported to be effective in improving symptoms of chronic sinusitis.<ref name=Weissm-etal-2011> Template:Cite journal </ref>

Xylitol can also be incorporated into fabrics to produce a cooling fabric. When moisture, such as sweat, comes into contact with the xylitol embedded in the fabric, it produces a cooling sensation.<ref>Template:Cite journal</ref>

Food properties

Nutrition, taste, and cooking

Humans absorb xylitol more slowly than sucrose, and xylitol supplies 40% fewer calories than an equal mass of sucrose.<ref name=Drugs-2018/>

Xylitol has about the same sweetness as sucrose,<ref name=Drugs-2018/> but is sweeter than similar compounds like sorbitol and mannitol.<ref name=Ur-Rehman-etal-2015> Template:Cite journal </ref>

Xylitol is stable enough to be used in baking,<ref name=UK-Diabetes-2018-10-28/> but because xylitol and other polyols are more heat-stable, they do not caramelise as sugars do. When used in foods, they lower the freezing point of the mixture.<ref name=leatherhead>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Food risks

No serious health risk exists in most humans for normal levels of consumption. The European Food Safety Authority has not set a limit on daily intake of xylitol. Due to the adverse laxative effect that all polyols have on the digestive system in high doses, xylitol is banned from soft drinks in the European Union. Similarly, due to a 1985 report by the E.U. Scientific Committee on Food which states that "ingesting 50 g a day of xylitol can cause diarrhea", tabletop sweeteners (as well as other products containing xylitol) are required to display the warning "Excessive consumption may induce laxative effects".<ref name=UK-NHS-2016-04-13> {{#invoke:citation/CS1|citation |CitationClass=web }} </ref>

Metabolism

Xylitol has 2.4 kilocalories of food energy per gram of xylitol (10 kilojoules per gram) according to U.S. and E.U. food-labeling regulations.<ref name=UN-FAO-y5022e04> Template:Cite report </ref><ref name=EAPP-Food-legtn/> The real value can vary, depending on metabolic factors.<ref name="Livesey-2003" />

Primarily, the liver metabolizes absorbed xylitol. The main metabolic route in humans occurs in cytoplasm, via nonspecific NAD-dependent dehydrogenase (polyol dehydrogenase), which transforms xylitol to [[D-xylulose|Template:Sc-xylulose]]. Specific xylulokinase phosphorylates it to [[D-xylulose-5-phosphate|Template:Sc-xylulose-5-phosphate]]. This then goes to pentose phosphate pathway for further processing.<ref name=Livesey-2003/>

About 50% of eaten xylitol is absorbed via the intestines. Of the remaining 50% that is not absorbed by the intestines, in humans, 50–75% of the xylitol remaining in the gut is fermented by gut bacteria into short-chain organic acids and gases, which may produce flatulence. The remnant unabsorbed xylitol that escapes fermentation is excreted unchanged, mostly in feces; less than 2 g of xylitol out of every 100 g ingested is excreted via urine.<ref name=Livesey-2003> Template:Cite journal </ref>

Xylitol ingestion also increases motilin secretion, which may be related to xylitol's ability to cause diarrhea.<ref name=Wölnerhn-etal-2019> Template:Cite journal </ref> The less-digestible but fermentable nature of xylitol also contributes to constipation relieving effects.<ref name=Salli-etal-2019/>

Health effects

Dental care

A 2015 Cochrane review of ten studies between 1991 and 2014 suggested a positive effect in reducing tooth decay of xylitol-containing fluoride toothpastes when compared to fluoride-only toothpaste, but there was insufficient evidence to determine whether other xylitol-containing products can prevent tooth decay in infants, children or adults.<ref name="pmid25809586">Template:Cite journal</ref> Subsequent reviews support the belief that xylitol can suppress the growth of pathogenic Streptococcus in the mouth, thereby reducing dental cavities and gingivitis, although there is concern that swallowed xylitol may cause intestinal dysbiosis.<ref name="pmid32638045">Template:Cite journal</ref><ref name="pmid35462747">Template:Cite journal</ref><ref name="pmid31060040">Template:Cite journal</ref> A 2022 review suggested that xylitol-containing chewing gum decreases plaque, but not xylitol-containing candy.<ref>Template:Cite journal</ref>

Earache

In 2011 EFSA "concluded that there was not enough evidence to support" the claim that xylitol-sweetened gum could prevent middle-ear infections, also known as acute otitis media (AOM).<ref name=UK-NHS-2016-04-13/><ref> Template:Cite journal </ref> A 2016 review indicated that xylitol in chewing gum or a syrup may have a moderate effect in preventing AOM in healthy children.<ref name=Azarpazh-etal-2016> Template:Cite journal </ref> It may be an alternative to conventional therapies (such as antibiotics) to lower risk of earache in healthy children – reducing risk of occurrence by 25%<ref name=Marom-etal-2016> Template:Cite journal </ref> – although there is no definitive proof that it could be used as a therapy for earache.<ref name=Azarpazh-etal-2016/>

Diabetes

In 2011, EFSA approved a marketing claim that foods or beverages containing xylitol or similar sugar replacers cause lower blood glucose and lower insulin responses compared to sugar-containing foods or drinks.<ref name=UK-Diabetes-2018-10-28> {{#invoke:citation/CS1|citation |CitationClass=web }} </ref><ref name=EFSA-2011> Template:Cite journal </ref> Xylitol products are used as sucrose substitutes for weight control,<ref name=UK-Diabetes-2018-10-28/><ref name=Salli-etal-2019> Template:Cite journal </ref> as xylitol has 40% fewer calories than sucrose (2.4 kcal/g compared to 4.0 kcal/g for sucrose).<ref name=UK-Diabetes-2018-10-28/><ref name=Tiefenbkr-2017> Template:Cite book </ref> The glycemic index (GI) of xylitol is only 7% of the GI for glucose.<ref name=Foster-Powell-etal-2002> Template:Cite journal </ref>

Adverse effects

Humans

When ingested at high doses, xylitol and other polyols may cause gastrointestinal discomfort, including flatulence, diarrhea, and irritable bowel syndrome (see Metabolism above); some people experience the adverse effects at lower doses.<ref name=UK-NHS-2016-04-13/><ref name=Mäkinen-2016> Template:Cite journal </ref> Xylitol has a lower laxation threshold than some sugar alcohols but is more easily tolerated than mannitol and sorbitol.<ref name=Can-Diabetes-2005-05-01> Template:Cite report </ref>

Increased xylitol consumption can increase oxalate, calcium, and phosphate excretion to urine (termed oxaluria, calciuria, and phosphaturia, respectively). These are known risk factors for kidney stone disease, but despite that, xylitol has not been linked to kidney disease in humans.<ref name=Janket-etal-2019> Template:Cite journal </ref>

Dogs and other animals

Xylitol is poisonous to dogs.<ref name="dogs-fda">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Ingesting 100 milligrams of xylitol per kilogram of body weight (mg/kg bw) causes dogs to experience a dose-dependent insulin release; depending on the dose it can result in life-threatening hypoglycemia. Hypoglycemic symptoms of xylitol toxicity may arise as quickly as 30 to 60 minutes after ingestion. Vomiting is a common first symptom, which can be followed by tiredness and ataxia. At doses above 500 mg/kg bw, liver failure is likely and may result in coagulopathies like disseminated intravascular coagulation.<ref name="Schmid-Hovda-2016"> Template:Cite journal </ref>

Xylitol is safe for rhesus macaques, horses, and rats.<ref name="Schmid-Hovda-2016" />

A 2018 study suggests that xylitol is safe for cats in doses of up to 1000 mg/kg; however, this study was performed on only 6 cats and should not be considered definitive.<ref name="Jerzsele-etal-2018"> Template:Cite journal </ref>

See also

• Aspartame
• Birch sap
• [[L-xylulose reductase|Template:Sc-Xylulose reductase]]
• Xylonic acid

External links

• Template:Commons category inline