Disaccharide of Lactose

Lactose, as a unique carbohydrate in most mammalian milks, has been part of the human diet since human very origin. Nowadays, because of its chemical characteristics, lactose is found in many milk-derived products and is an important raw material in pharmaceutical products.

Lactose is a disaccharide that yields D-glucose and D-galactose on hydrolysis. The two monosaccharides are linked through the aldehyde group of D-galactose; thus, the aldehydic portion of lactose is on the glucose residue.

Its biosynthesis takes place in the mammary gland. Concentrations in milk vary strongly with species. Lactose is the first and only carbohydrate every newborn mammal (including human) consumes in significant amounts. Bovine milk contains 45 – 50 grams lactose per liter.

Sweetness of lactose is much less than that of glucose, galactose, or sucrose. This, coupled with its comparatively low solubility, restricts its applications as a sweetener.

In milk, lactose exists in two isomeric forms, called α- and β- lactose respectively. 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.

In the gut, lactose needs to be broken down into its monosaccharides in order to be efficiently absorbed in the small intestine. Lactose usually is hydrolyzed by β-galactosidase (lactase) and absorbed as glucose and galactose. β-galactosidase or also known as lactase phlorizin hydrolase (LPH)) is a homodimeric enzyme anchored to the membranes of the small intestinal villus tips.

The body then absorbs these simpler sugars (glucose and galactose) into the bloodstream. Lactase deficiency and lactose malabsorption may lead to lactose intolerance. Lactose intolerance is a condition in which people have digestive symptoms—such as bloating, diarrhea, and gas—after eating or drinking milk or milk products.
Disaccharide of Lactose