Lactose

Lactose
Identifiers
CAS number	[63-42-3]
PubChem	6134
MeSH	Lactose
Properties
Molecular formula	C12H22O11
Molar mass	342.296
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Lactose (also referred to as milk sugar) is a sugar which is found most notably in milk. Lactose makes up around 2–8% of milk (by weight). The name comes from the Latin word for milk, plus the -ose ending used to name sugars. Its systematic name is β-D-galactopyranosyl-(1↔4)α-D-glucopyranose.

Chemistry

Lactose is a disaccharide that consists of β-D-galactose and β-D-glucose molecules bonded through a β1-4 glycosidic linkage.

Solubility

Lactose has a solubility of 1 in 4.63 measured %w/v. This translates to 0.216 g of lactose dissolving readily in 1 mL of water.

The solubility of lactose in water is 18.9049 g at 25°C, 25.1484 g at 40°C and 37.2149 g at 60°C per 100 g solution. Its solubility in ethanol is 0.0111 g at 40°C and 0.0270 g at 60°C per 100 g solution.Machado, José J.B.; João A. Coutinho, Eugénia A. Macedo (2000). "Solid–liquid equilibrium of a-lactose in ethanol/water" (PDF). Fluid Phase Equilibria. Retrieved on 2007-12-05. 

Digestion of lactose

Main article: Lactose intolerance

Infant mammals are fed on milk by their mothers. To digest it an enzyme called lactase (β-D-galactosidase) is secreted by the intestinal villi, and this enzyme cleaves the molecule into its two subunits glucose and galactose for absorption.

Since lactose occurs mostly in milk, in most mammals the production of lactase gradually decreases with maturity.

Many people with ancestry in Europe, the Middle East, India, or parts of East Africa, maintain normal lactase production into adulthood. In many of these cultures, mammals such as cattle, goats, and sheep are milked for food. Hence, it was in these regions that genes for lifelong lactase production first evolved.Nicholas Wade. "Study Detects Recent Instance of Human Evolution", The New York Times, December 10, 2006. Retrieved on 2007-12-05. 

References

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