Disaccharide

Sucrose, a common disaccharide

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

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.

Common disaccharides

• Sucrose (known as table sugar, cane sugar, saccharose, or beet sugar) is composed of glucose + fructose.
• Lactose (milk sugar) is glucose + galactose.
• Maltose is produced during the malting of barley.

It is a glucose + glucose disaccharide, where its glucose monomers are connected with a α(1→4) bond.

• Trehalose is present in fungi and insects.

It is also a glucose + glucose disaccharide, where its glucose monomers are connected with a α(1→1)α bond. Trehalose has been successfully produced at an industial scale by enzymatic treatment of starch for use as a food ingredient.

• Cellobiose is another of the glucose + glucose + porn disaccharides, where its glucose monomers are connected with a β(1→4) bond.

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