| |
|
Molecular structure
Lactose is a carbohydrate, and as such a disaccharide. One Molecule of lactose consists of one molecule each of two other carbohydrates, i.e. galactose and glucose. These galactose and glucose moieties, as they are called, are linked together by means of what is known as a beta-(1,4) glucosidic linkage. The molecular structure of lactose is depicted below.
Molecular structure of lactose
The official chemical name of lactose, as frequently encountered in regulatory documents such as the Pharmacopoeia , is:
4-O-β-D-galactopyranosyl, D-glucopyranose.
α / β-isomery
In milk, lactose is present in two isomeric forms called α- and β-lactose. The molecular structures of α- and β-lactose differ in the orientation of a hydrogen and a hydroxyl group on carbon atom no. 1 in the glucose moiety. Both forms change into one another continuously. This phenomenon is called mutarotation. The velocity of mutarotation is determined by factors such as temperature, concentration, and pH (acidity) of the solution.
Lactose solutions seek a state of equilibrium between the α and the β form. At room temperature, the equilibrium results in a ratio of about 40% α-lactose and 60% β-lactose. The fact that two forms of lactose exist that differ in molecular structure has profound effects on various properties of lactose, such as its solid state properties, crystal morphology and solubility. |
