Disaccharides are formed from two monosaccharides, covalently linked together. The hydrolysis of a disaccharide may yield two molecules of the same or different monosaccharides. The three important disaccharides are sucrose, maltose and lactose.
The bond between two monosaccharides is called a glycosidic linkage or a glycosidic bond. The two monosaccharides are joined together through an oxygen atom.
Sucrose is obtained from sugarcane or sugar beets. It has the chemical formula, C12
Sucrose is made up of one unit of glucose — specifically, the alpha anomer alpha D glucopyranose — and one unit of fructose — specifically, the beta anomer beta D fructofuranose. Sucrose gives a negative test with sucrose gives a negative test with reagents. Hence, sucrose is called a non-reducing sugar.
Maltose is another important disaccharide, which contains two glucose units.
Lactose is a disaccharide present in milk
Lactose is made from beta-D-galactose and beta-D-glucose