Chemistry of lactose

 Lactose, commonly known as milk sugar, is a disaccharide found primarily in milk and dairy products. Its chemistry is quite interesting because it's made up of two simpler sugars (monosaccharides): glucose and galactose. Here’s a breakdown of its chemistry:

Structure of Lactose

1. Composition: Lactose is a disaccharide, meaning it’s composed of two monosaccharides. In lactose, these two monosaccharides are D-glucose and D-galactose.
2. Linkage: These two monosaccharides are linked by a β(1→4) glycosidic bond. Specifically, the hydroxyl group on carbon 1 (C1) of galactose is linked to the hydroxyl group on carbon 4 (C4) of glucose.
3. Forms of Lactose: Lactose can exist in two forms:
   • α-Lactose: Where the anomeric (C1) hydroxyl group of the glucose unit is oriented downward.
   • β-Lactose: Where the anomeric hydroxyl group of glucose is oriented upward.
   • These forms interconvert in solution due to a process called mutarotation, where the bond around the C1 carbon rotates.

Chemical Properties of Lactose

1. Reducing Sugar: Lactose is a reducing sugar because it has a free anomeric carbon (C1 of glucose) that can open up and react. This means it can participate in reactions where it reduces other compounds, typically under alkaline conditions.
2. Hydrolysis: Lactose can be hydrolyzed into glucose and galactose by the enzyme lactase. Hydrolysis breaks the glycosidic bond through the addition of a water molecule, a reaction that takes place in the small intestine in humans.
3. Optical Activity: Lactose exhibits optical activity, meaning it can rotate plane-polarized light due to its chiral centers. The degree and direction of this rotation depend on the concentration of α- and β- forms of lactose in solution.

Biological Role and Digestion

• Source of Energy: Lactose provides a source of energy, especially in young mammals. After ingestion, lactose is broken down into glucose and galactose, which are then absorbed into the bloodstream and used for energy.
• Lactose Intolerance: Some people lack the enzyme lactase, leading to a condition called lactose intolerance, where lactose remains undigested in the intestine, causing digestive symptoms.

Importance in Pharmacy and Food Chemistry

Lactose is widely used as an excipient in the pharmaceutical industry due to its stability and inertness. It also plays a role in food chemistry, as lactose can undergo the Maillard reaction with amino acids, which contributes to the browning and flavor development of foods during cooking.