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Lactose (milk sugar)
IUPAC name
Other names
Milk sugar
63-42-3 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:36218 YesY
ChemSpider 5904 YesY
ECHA InfoCard 100.000.509
EC Number 200-559-2
PubChem 6134
Molar mass 342.30 g/mol
Appearance white solid
Density 1.525 g/cm3
Melting point 202.8 °C (397.0 °F; 475.9 K)
19.5 g/100 mL
5652 kJ/mol, 1351 kcal/mol, 16.5 kJ/g, 3.94 kcal/g
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 357.8 °C (676.0 °F; 631.0 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Lactose is a disaccharide sugar composed of galactose and glucose that is found in milk. Lactose makes up around 2–8% of milk (by weight), although the amount varies among species and individuals, and milk with a reduced amount of lactose also exists. It is extracted from sweet or sour whey. The name comes from lac (gen. lactis), the Latin word for milk, plus the -ose ending used to name sugars. It has a formula of C12H22O11 and the hydrate formula C12H22O11·H2O, making it an isomer of sucrose.

The first crude isolation of lactose, by Italian physician Fabrizio Bartoletti (1576–1630), was published in 1633. In 1700, the Venetian pharmacist Lodovico Testi (1640–1707) published a booklet of testimonials to the power of milk sugar (saccharum lactis) to relieve, among other ailments, the symptoms of arthritis. In 1715, Testi's procedure for making milk sugar was published by Antonio Vallisneri. Lactose was identified as a sugar in 1780 by Carl Wilhelm Scheele.

In 1812, Heinrich Vogel (1778-1867) recognized that glucose was a product of hydrolyzing lactose. In 1856, Louis Pasteur crystallized the other component of lactose, galactose. By 1894, Emil Fischer had established the configurations of the component sugars.

Lactose was named by the French chemist Jean Baptiste André Dumas (1800-1884) in 1843.

Lactose is a disaccharide derived from the condensation of galactose and glucose, which form a β-1→4 glycosidic linkage. Its systematic name is β-D-galactopyranosyl-(1→4)-D-glucose. The glucose can be in either the α-pyranose form or the β-pyranose form, whereas the galactose can only have the β-pyranose form: hence α-lactose and β-lactose refer to the anomeric form of the glucopyranose ring alone.



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