Disaccharides | Maltose, Lactose, Sucrose |
Disaccharides.
A molecule of a disaccharides consists of two monosaccharide units linked together in the form of an acetal (a glycosidic linkage). On hydrolysis, it yields these units. A large number of disaccharides are found in nature. They are crystalline, water-soluble, and sweet compounds. Maltose, lactose, and sucrose, are the commonly occurring natural disaccharides. On hydrolysis, they yield two molecules of monosaccharides each as given below;
The two monosaccharide units may be linked either through the anomeric — OH of one and an alcoholic group of the other (e. g., reducing disaccharides, maltose, and lactose) or through the anomeric -OH of both the units (e.g., non-reducing disaccharide, sucrose).
The structure of a disaccharide is established through the following steps:
- Hydrolysis and subsequent identification of the component monosaccharide units.
- Determination of the type of ring (furanose or pyranose) in each of the monosaccharide units.
- Location of the position of the linkage in one unit through which it is attached to the other unit.
- Finally, the anomeric configuration (α or β-) of the linkage is established through hydrolysis.