Disaccharide sugar of lactose

In disaccharides, pairs of single sugars are linked together. Three disaccharides are important in nutrition: maltose, sucrose and lactose.

All three have glucose as one of the single sugars.

Lactose is the principle carbohydrate of milk. Lactose gives milk and other dairy products a slightly sweet taste. Most human infants are born with the digestive enzymes necessary to split lactose into its two monosaccharide parts, glucose and galactose so as to absorb it.

Lactose

Lactose is the only disaccharide that has a beta glycosidic bond between the monosaccharides. It is often referred to as milk sugar and is sometimes added to processed foods.

During lactation, enzymes in the mammary glands combine glucose and galactose to produce lactose. 

Lactose can exist in a number of different physical forms depending on the method of production.

In aqueous solution, lactose exists as an anomeric mixture of alpha and beta forms. In the solid for, lactose usually crystallizes in its alpha form as a monohydrate.
Disaccharide sugar of lactose