Lactose is a disaccharide, a type of carbohydrate, composed of one molecule of glucose and one molecule of galactose linked together by a β-1,4-glycosidic bond. It is commonly found in the milk of mammals and is often referred to as milk sugar. Lactose is a significant energy source for infants, and the enzyme lactase facilitates digestion.

In its crystalline form, lactose is a white, water-soluble powder with a mildly sweet taste. The digestive enzyme lactase breaks down lactose into its constituent monosaccharides, glucose, and galactose, during the digestive process. Some individuals, particularly those with lactose intolerance, have reduced levels of lactase, leading to difficulty digesting lactose and resulting in symptoms such as bloating and gastrointestinal discomfort after consuming dairy products.

Various food products commonly use lactose as an ingredient, and individuals who have difficulty digesting this disaccharide can find lactose-free alternatives.

In this representation:

“C” represents a carbon atom.

“H” represents a hydrogen atom.

“O” represents an oxygen atom.

“||” represents the β-1,4- glycosidic bond.

Each vertical line between carbon atoms represents a single covalent bond.

This structure illustrates the linkage between the carbon atom at the first position of glucose and the carbon atom at the fourth position of galactose, forming the glycosidic bond. Lactose, a source of energy for infants, is commonly present in milk. The enzyme lactase is necessary to break down lactose into its constituent glucose and galactose molecules during digestion.