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A disaccharide with a chemical formula of C12H22O11 that occurs in human and bovine milk, and formed by the joining of glucose and galactose


Carbohydrates are one of the major classes of biomolecules. They are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides. The simplest form of carbohydrates is a monosaccharide. Combining two monosaccharides by a glycosidic linkage forms a disaccharide. Lactose is one of the most common types of disaccharides; others are sucrose and maltose.

Lactose is a disaccharide comprised of glucose and galactose linked together by a β-1→4 glycosidic linkage. Similar to sucrose and maltose, lactose has a general formula of C12H22O11.

Lactose is digested or broken down into its monosaccharide units through hydrolysis with the help of the enzyme, lactase. The bond that joins the two monosaccharides is broken, converting lactose to glucose and galactose. People who are lactose intolerant cannot digest or break down lactose. This becomes food for gas-producing gut flora. This could lead to gastrointestinal disturbance and flatulence.

Lactose is produced naturally and is present in milk of mammals, including humans. It is collected from bovine to be used in preparing infant formulas. A cow's milk, in particular, has about 4.7% lactose.

Lactose can be converted to lactic acid. Microorganisms, such as Lactobacilli, can convert lactose to lactic acid, which is used in the food industry, e.g. in the production of dairy products like yoghurt and cheese.

Word origin: Latin lac ("milk") + -ose

IUPAC name:

  • β-D-galactopyranosyl-(1→4)-D-glucose

Chemical formula:

  • C12H22O11


  • Milk sugar
  • 4-O-β-D-galactopyranosyl-D-glucose

See also:

Related terms: