Polyols from starch: General points in the method of manufacture

Maltitol and maltitol syrup E965

Maltitol is produced commercially by catalytic hydrogenation of D-maltose. D-Maltose is a naturally occurring disaccharide and is a major constituent of malt wort. Industrially maltose is obtained by the enzymic hydrolysis of highly purified starch. Maltitol is a hydrogenated disaccharide having the empirical formula C12H24O11.

Industrially in the manufacture of maltitol, the raw material used for the hydrogenation is a high maltose glucose syrup. High maltose glucose syrups are products with a high content of maltose (>50%) produced by an accurately controlled hydrolysis of purified starch using appropriate enzymes. In addition to maltose itself, these syrups contain higher molecular weight saccharide species (oligo- and polysaccharides). Maltitol syrups with maltitol contents ranging from 50-55% (Lycasin®) to 85% and higher are commercially available. A very pure maltitol (chemical purity >99%) is produced by a patented process (Devos and Gouy, 1985).

Mannitol E421

Mannitol takes its name from manna, a sweet exudate from the manna ash (Fraxinus ornus), of which it is the major constituent. Mannitol also occurs in olives, figs, and larches, in certain species of edible fungi, and in seaweed (Larninaria species).

D-Mannitol was originally obtained industrially by an extraction process; today it is produced by catalytic hydrogenation of D-fructose. Fructose is itself produced from invert sugar or starch. Through hydrogenation, a molecule of hydrogen is added to the ketone group of fructose, thus reducing it to a hydroxyl group. Mannitol is described as a hexitol, having six alcohol groups.

Sorbitol E420

Sorbitol takes its name from the sorbus tree (Sorbus aucuparia, the rowan or mountain ash) from the berries of which it was first extracted in 1872. It occurs widely in nature in many fruits and vegetables, and in fact is also present in carbohydrate metabolism in man.

D-Sorbitol is produced commercially by catalytic hydrogenation of D-glucose (dextrose). D-Glucose is also abundant in nature. It is also obtained by enzymatic hydrolysis of highly purified starch. The hydrogenation of dextrose involves the addition of a molecule of hydrogen to the aldehyde group (which exists as a hemiacetal in the pyranose ring form of D-glucose). The aldehyde group is thus reduced to an hydroxyl, or alcohol group. Sorbitol, like mannitol, is therefore a hexitol containing six alcohol groups.

Xylitol E967

Xylitol is present in many fruits and vegetables (e.g. greengages, strawberries, raspberries and cauliflowers) and is also naturally present in the human body. Xylitol is produced commercially by catalytic hydrogenation of the five carbon sugar xylose. This in turn is derived from xylan extracted from the hemicelluloses occurring in corn cobs, almond shells and birch bark. As in the production of sorbitol, a molecule of hydrogen is added to the aldehyde group of xylose, thus reducing it to an hydroxyl group. Xylitol, having five alcohol groups is a pentitol.

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