AskDefine | Define lactose

Dictionary Definition

lactose n : a sugar comprising one glucose molecule linked to a galactose molecule; occurs only in milk; "cow's milk contains about 4.7% lactose" [syn: milk sugar]

User Contributed Dictionary



  1. The disaccharide sugar of milk and dairy products, C12H22O11, (a product of glucose and galactose) used as a food and in medicinal compounds.


disaccharide sugar of milk and dairy products
  • Catalan: lactosa
  • Czech: laktóza
  • Danish: laktose
  • French: lactose
  • Italian: lattosio
  • Spanish: lactosa

Extensive Definition

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)β-D-glucopyranose.


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


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.

Digestion of lactose

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. The genes of lactose tolerance have evolved independently in various ethnic groups.


lactose in Arabic: لاكتوز
lactose in Bulgarian: Лактоза
lactose in Catalan: Lactosa
lactose in Czech: Laktóza
lactose in Welsh: Lactos
lactose in Danish: Laktose
lactose in German: Milchzucker
lactose in Spanish: Lactosa
lactose in Esperanto: Laktozo
lactose in Basque: Laktosa
lactose in French: Lactose
lactose in Icelandic: Laktósi
lactose in Italian: Lattosio
lactose in Hebrew: לקטוז
lactose in Latin: Lactosium
lactose in Lithuanian: Laktozė
lactose in Hungarian: Laktóz
lactose in Macedonian: Лактоза
lactose in Malay (macrolanguage): Laktosa
lactose in Dutch: Lactose
lactose in Japanese: ラクトース
lactose in Norwegian: Laktose
lactose in Norwegian Nynorsk: Laktose
lactose in Occitan (post 1500): Lactòsa
lactose in Polish: Laktoza
lactose in Portuguese: Lactose
lactose in Russian: Лактоза
lactose in Albanian: Laktoza
lactose in Simple English: Lactose
lactose in Slovenian: Laktoza
lactose in Serbian: Лактоза
lactose in Serbo-Croatian: Laktoza
lactose in Finnish: Laktoosi
lactose in Swedish: Laktos
lactose in Turkish: Laktoz
lactose in Ukrainian: Лактоза
lactose in Chinese: 乳糖
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