disaccharide - Chemistry, Common disaccharides

A carbohydrate consisting of two simple sugars joined together, condensed with the elimination of water. The most abundant in nature are sucrose (table sugar) which combines one glucose and one fructose molecule, and lactose, the sugar of milk, which is a combination of glucose and galactose. Fructose, glucose, and galactose are single-unit sugars, classed as monosaccharides.

A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides and is found in plant seeds.

Chemistry

The two monosaccharides are bonded via a condensation reaction that leads to the loss of a molecule of water. 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. It is a glucose + glucose disaccharide, where its glucose monomers are connected with a α(1→4) bond. It is also a glucose + glucose disaccharide, where its glucose monomers are connected with a α(1→1)α bond. Cellobiose is another of the glucose + glucose disaccharides, where its glucose monomers are connected with a β(1→4) bond.