Xylitol

Chemical Structure

Xylitol

Skeletal Formula & Structure

Name: xylitol (also called 1,2,3,4,5-pentane-pentol; sometimes written xylite)

Class: a sugar alcohol (polyol) derived from a five-carbon sugar (xylose).

Molecular formula: C₅H₁₂O₅.

Molar mass: ~152.146 g·mol⁻¹.

Structure (description): five carbon backbone with one hydroxyl (–OH) on each carbon (a pentitol). It is achiral overall? — in practice xylitol has stereocenters at carbons 2,3,4 so it is a meso form of a pentitol (the common xylitol used industrially is the meso-isomer). You can think of it as the reduced (alcohol) form of the sugar xylose (the aldehyde group reduced to a hydroxyl).

Physical properties (typical): white crystalline solid; very soluble in water; sweet taste roughly comparable to sucrose (table sugar) but with a slightly cooling sensation on dissolution.

Group Classification & Stereoisomers

Sugar alcohols (polyols) are carbohydrate-derived compounds in which the carbonyl group of a sugar has been reduced to an alcohol, giving them sweetness with fewer calories and a lower glycemic impact than sucrose. They occur naturally in fruits and vegetables but are also produced industrially for use as bulk sweeteners, humectants, and stabilizers. Common sugar alcohols include xylitol, sorbitol, mannitol, erythritol, maltitol, isomalt, and lactitol. While generally safe, they can cause gastrointestinal discomfort at high intake levels, and xylitol is notably toxic to dogs.

Stereoisomers are molecules that share the same molecular formula and connectivity but differ in the three-dimensional arrangement of their atoms, giving them distinct spatial orientations. Pentitols (five-carbon sugar alcohols) have three chiral centers, meaning they can form multiple stereoisomers depending on how the hydroxyl groups point left or right in a Fischer projection. Xylitol itself is most commonly found as the meso stereoisomer, where the symmetry of substituents cancels overall chirality. Its other possible pentitol stereoisomers include D-xylitol and L-xylitol (mirror‐image enantiomers), along with related but differently arranged pentitols such as arabitol, ribitol, and lyxitol, each defined by a unique pattern of hydroxyl orientations along the carbon chain.

Arabinitol

Also called: L-arabitol or D-arabitol (two enantiomeric forms).

Derived from: arabinose.

Occurrence: Found in fungi, yeasts, and some plants.

Uses/importance:

Biomarker in clinical medicine: D-arabitol is elevated in invasive candidiasis; used as a diagnostic indicator.
Emerging interest as a bio-based platform chemical (similar to xylitol).
Sweetness is less than sucrose; not widely used commercially as a sweetener.

Ribitol

Also called: adonitol.

Derived from: ribose (reducing the aldehyde).

Biological role:

Component of riboflavin (vitamin B₂) — the ribitol moiety forms part of the vitamin structure.
Occurs in certain bacterial teichoic acids (cell-wall components in Gram-positive bacteria).

Uses: Mostly biochemical; not used as a food additive.

D-lyxitol

Derived from: lyxose (a relatively rare aldopentose).

Occurrence: Rare in nature; appears mostly in specialized metabolic contexts or as a lab chemical.

Uses: Research chemical; no major industrial applications; not used as a sweetener.

History

Xylitol was first isolated in 1891 by Emil Fischer (with his student/assistant Rudolf Stahel), who reduced the sugar D‑xylose (xýlon (ξύλον) — Greek for “wood”) to get a syrup of what they called “xylit.” Source

Around the same time (also 1891), a French chemist M. G. Bertrand independently isolated xylitol — or at least a xylitol-containing syrup — from wheat and oat straw. Source

Thus the “discovery” of xylitol is credited to both Fischer & Stahel (Germany) and Bertrand (France), depending on source. Source

In the 1950s, work by researchers such as Oscar Touster (in Nashville, Tennessee) revealed that xylitol is formed endogenously in humans as part of carbohydrate metabolism; this re-awoke interest in its physiological role. ProQuest+1

The next big turning point came during World War II: sugar shortages in Europe spurred interest in alternatives, and xylitol — which could be derived from wood or plant biomass — became a valuable substitute. Wikipedia+2ScienceDirect+2

By around 1975, the first xylitol-containing chewing gum (and other confections) was launched on the market — notably in Finland (for example under the brand Jenkki) — marking the start of xylitol’s use as a consumer sweetener rather than just a lab/industrial chemical. Oral Health Group+2Wikipedia+2

Modern Sourcing

Catalytic hydrogenation of xylose

The most common industrial route. Hemicellulose in hardwoods (birch, beech), corncobs, sugarcane bagasse and other biomass yields xylose on hydrolysis; xylose is then hydrogenated (catalytic reduction) to xylitol. Advances in fermentation and biocatalysis aim to reduce energy use and increase sustainability.

Chemical/enzymatic routes

Lab and specialty processes can convert pentoses enzymatically or chemically; some methods use biocatalysts for better selectivity. Microbial fermentation from xylose or even directly from lignocellulosic feedstocks is an area of active development; engineered microbes can convert pentoses to xylitol, offering routes that may be greener or use lower-grade biomass.

China is the world’s leading xylitol producer. Several recent market-studies put China at ~70–75% of global xylitol output. PW Consulting+2Intel Marke

Europe’s production tends to focus on high-quality / high-purity xylitol (e.g. for food, oral-care or pharmaceutical use). For example, a major European producer with such a focus is Danisco Sweeteners in Finland. Research and Markets+1

Global demand and trade suggests xylitol is economically viable For bulk food-grade xylitol (typical ≥ 99% purity) purchased wholesale in kilogram quantities, a common FOB price range is about US $4.80 to $6.50 per kg. Alibaba+1

Applications

Food & confectionery

Xylitol is used as a bulk sweetener in sugar-free chewing gums, candies, mints, baked goods (formulation differences vs sucrose), and beverages. Preferred where chewiness and mouthfeel of a sugar alcohol are desirable.

Oral care & health products

Xylitol is used in toothpastes, mouthwashes, chewing gum and lozenges for anti-cavity benefit and to reduce plaque formation.

Cosmetics & toiletries

Xylitol is used as a humectant/moisturizer in lotions, creams and some personal care products.

Biological & Human Impacts

Xylitol protects teeth by stopping the bacteria that produce acid. Xylitol interferes with bacterial metabolism through a “futile cycle” that disrupts energy production in certain oral bacteria—especially Streptococcus mutans, the primary cavity-causing organism.

1. Xylitol is taken up by bacteria via the PTS transporter

Streptococcus mutans mistakes xylitol for a metabolizable sugar and transports it into the cell using the phosphoenolpyruvate (PEP) phosphotransferase system (PTS)—the same system used for sugars like fructose.

During uptake, bacteria convert xylitol → xylitol-5-phosphate (X5P).
Problem: S. mutans cannot metabolize X5P.

2. Xylitol-5-phosphate is toxic to the bacterium

Once inside, X5P accumulates and becomes a metabolic “dead end.”
Because the cell cannot use or store it, bacteria must dephosphorylate and expel it back out.

3. This creates a “Futile Cycle” that wastes ATP

Every cycle of:

Importing xylitol
Phosphorylating it (consumes energy indirectly through PEP)
Dephosphorylating and exporting it

…forces S. mutans to burn energy with zero nutritional gain.

This repeated cycle drains cellular energy and slows the bacterium’s growth rate.

Humans have the ability to fully metabolize Xylitol through a different pathway. The resulting energy gain nets approximately 2.4 kCal per gram.

The calories and glycemic index should both be evaluated when considering a sugar-alcohol sweetener substitute.

1. Organs/cells involved

Humans metabolize xylitol mainly in:

Liver hepatocytes (≈90% of metabolism)
Kidney cells
Adipose tissue cells
These cells express the necessary enzymes for the polyol pathway.

2. Human metabolic pathway

Xylitol → D-xylulose
Enzyme: Xylitol dehydrogenase (a NAD⁺-dependent dehydrogenase)
D-xylulose → D-xylulose-5-phosphate
Enzyme: Xylulokinase (ATP-dependent)
D-xylulose-5-phosphate enters the pentose phosphate pathway (PPP)
- Generates NADPH for antioxidant defenses
- Produces ribose-5-phosphate (nucleic acid precursor)
  Interconverts with glycolytic intermediates

Xylitol is sweet for us, but way too sweet for dogs. They suffer from a massive insulin spike which could lead to hypoglycemia

Xylitol is toxic to dogs because their pancreas mistakes xylitol for glucose, triggering a massive, rapid release of insulin—far more than in humans. This causes life-threatening hypoglycemia within minutes to hours. In larger exposures, xylitol also causes acute liver failure. Both effects stem from key metabolic differences between dogs and humans.

Dogs absorb xylitol from the gut 5–10× faster than humans.

Dogs have a unique GLUT2–dependent sensing mechanism in pancreatic β-cells.

Dog β-cells take up xylitol.
They incorrectly interpret its arrival as a glucose surge.
This causes excessive insulin release.

Humans do not secrete insulin in response to xylitol.

Plasma levels spike within 30 minutes, triggering strong metabolic responses.

Enzyme deficiency:

Dogs have insufficient xylitol dehydrogenase (XD) activity, which converts:
Xylitol → D-xylulose

Because dogs cannot efficiently perform this step, xylitol metabolism stalls.

Consequences of this enzyme deficiency

Xylitol accumulates in hepatocytes
Causes ATP depletion
Leads to massive oxidative stress
Triggers mitochondrial damage
Results in hepatic necrosis and acute liver failure

This is why high doses or delayed treatment lead to liver damage.

Xylitol OC (5 points)

Find a sugar substitute at home. Take picture evidence of that ingredient label. Create a Google slide show that showcases the following slides:

1 - Picture evidence of the substitute at home (if none in home, you may go to a store and take a picture there). Include your name in the picture to verify you took the picture!

2 - Show the line/lewis structure of the molecule. How does it compare to the other carbohydrates we have covered?

3 - Include the calorie and glycemic index values for that sugar substitute

4 - A brief synopsis of how that substitute is sourced/made

5 - Any health concerns or impacts

Possible substitutes - Polyols [Sorbitol, Mannitol,

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