Lactose is a disaccharide carbohydrate(made up of two monosaccharide units) composed of β-D-galactose and β-D-glucose units. Hydrolysis breaks the glycosidic bond converting sucrose into β-D-galactose and β-D-glucose.

NOTE: But however, this reaction is so slow that it takes years for the solution of sucrose to undergo negligible change. Hence an enzyme called sucrase is added to proceed rapidly.