sweeteners

Xylitol

Industrial production of Xylitol

Xylitol is a polyol with 5 carbon atoms, with sweetness similar to that of sucrose (polyols, or polyalcohols, are carbohydrates with a molecule similar to monosaccharides, but with a hydroxyl function instead of aldehyde or ketonic).

Xylitol is found in small amounts in a series of fruits and vegetables and is formed in the human body, as an intermediate, during glucose metabolism. Synthesized for the first time and described by Emil Fischer in 1891, xylitol has been used in the human diet as a sweetener since the 1960s.

On a commercial scale it is produced by chemical conversion of xylan. Sources of xylan are birch and other hardwoods, the shell of almonds and by-products of paper production. The content of xylan in these materials can vary considerably along with the presence of by-products (poles or oligosaccharides) that must be removed during the production processes. The commercial synthesis of xylitol includes 4 steps:

  1. disintegration of xylan-rich materials and xylan hydrolysis in xylose
  2. isolation of xylose from the hydrolyzate, by means of chromatographic processes, to obtain solutions containing pure xylose
  3. xylose is hydrogenated to xylitol in the presence of nickel-based catalysts
  4. crystallization of xylitol.

Although in principle enzymatic processes can be used, these procedures are not used for commercial-scale synthesis. Other synthetic approaches are known in the literature, but have a merely scientific interest

FORMULA

C 5 H 12 O 5

APPEARANCE

White crystalline powder

SMELLNobody
SPECIFIC ROTATIONIdle
MELTING RANGE

92-96 ° C

BOILING POINT216 ° C (760 mmHg)
SOLUBILITY at 20 ° C

169g / 100 ml H 2 O

pH IN 100 g / l H 2 O

5-7
SWEETENING POWER

Equal to sucrose

STABILITY'

Stable at 120 ° C, it does not caramelize unless it is heated to boiling temperature for a few minutes

Xylitol as a sweetener

Currently xylitol is used as a sweetener in many non-cariogenic sweets (chewing gum, chocolate, gummy candies) and less frequently in diet foods (eg products for diabetics), in pharmaceutical preparations (throat tablets, multivitamin tablets, syrups for cough) and in cosmetics (toothpaste and mouthwash). In small percentage, it is also added to drinks to improve the taste of the product and the profile of sweetness; on the label it can hide behind the code E967.

Theoretically, xylitol can also be used in baked goods. However, if the formation of the crust and brownish color and caramelization is required, it is necessary to add a reducing sugar. Xylitol also inhibits the growth and fermentative activity of yeasts, so its presence is not appropriate in products that require natural leavening yeasts.

The dissolution of polyols in water is an endothermic process (it absorbs heat), which involves a cooling of the solution higher than that supplied by the sucrose. This organoleptic property, which results in a sensation of freshness in the oral cavity, is widely exploited for the production of chewing gum. The cooling effect, in particular, enhances the perception of the mint aroma.

The cooling effect is obviously not felt if xylitol is already dissolved in the product in which it is contained (toothpastes, mouthwashes) or exists in an amorphous form (jellies in general).

Xylitol metabolism and nutritional properties

All polyols are slowly absorbed from the intestine, as their transport through the mucosa is not facilitated by a specific transport system. Therefore, after the ingestion of large quantities of xylitol only a small part is absorbed and conveyed into the enteropathic system (through the portal vein). Most of the ingested xylitol reaches the distal part of the digestive tract, where it undergoes the fermentation process by the local bacterial flora. Fermentation products are short or volatile fatty acids (acetates, propionates, butyrates), as well as small amounts of gas (H 2, CH 4, CO 2 ). Fatty acids are seized from the liver and used in mitochondria for the production of acetyl-CoA and propionyl-Co-A.

For xylitol and other polyols a calorific value of about 2.8-2.9 kcal / g has been estimated. This value derives from the consideration that only about ¼ of the totally ingested xylitol is absorbed in the intestinal tract. This portion, then metabolized by the glucuronate-pentose phosphate shunt, provides 4 kcal / mol. Unabsorbed ¾ are almost totally fermented by the intestinal flora. It has been estimated that 42% of the energy supplied by unabsorbed xylitol is consumed by the metabolism and growth of bacteria, while approximately 58% of the energy remains available to the body. In light of these considerations, the European community has set the caloric value of xylitol and other polyols at 2.4 kcal / g.

The results of tests conducted on animals (rats, cats, dogs) for the evaluation of xylitol toxicity, showed a very low toxicity, regardless of the route of administration and manifested only at high doses. Furthermore, xylitol is not mutagenic and is acariogenic (it does not cause tooth decay).

Tolerance to high doses of xylitol has been investigated in numerous studies in diabetic volunteers. The results of these studies have shown good tolerance even at high doses. No changes in clinical parameters were observed. The only side effect is a transient laxative effect, especially if xylitol is associated with slow-digesting carbohydrates.

See also: Xylitol in cosmetics