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DISACCHARIDE

A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides.

[edit] Chemistry

The two monosaccharides are bonded via a condensation reaction that leads to the loss of a molecule of water. The glycosidic bond can be formed between any hydroxyl group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha- or beta-) result in disaccharides that are diastereoisomers with different chemical and physical properties.

Depending on the monosaccharide constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweet-tasting. 'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharide, disaccharide, oligosaccharide, and polysaccharide).

[edit] Common disaccharides

Disaccharide Unit 1 Unit 2 Bond Notes
Sucrose (table sugar, cane sugar, saccharose, or beet sugar) glucose fructose α(1→2) -
Lactose (milk sugar) glucose galactose β(1→4) -
Maltose glucose glucose α(1→4) Produced during the malting of barley
Trehalose glucose glucose α(1→1)α Present in fungi and insects. Successfully produced at an industial scale by enzymatic treatment of starch for use as a food ingredient.
Cellobiose glucose glucose β(1→4) -

Maltose and cellobiose are hydrolysis products of the polysaccharides, starch and cellulose, respectively.