Lactose
From Wikipedia, the free encyclopedia
| Lactose | |
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| IUPAC name |
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| Other names | Milk sugar; (2S,3R,4R,5S,6R)-6-(hydroxymethyl)-5-((2S,3R,4S,5R,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yloxy)tetrahydro-2H-pyran-2,3,4-triol |
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| CAS number | [] |
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| Properties | |
| Molecular formula | C12H22O11 |
| Molar mass | 342.29648 g/mol |
| Appearance | white solid |
| Solubility in water | 0.216 g/mL |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Lactose (also referred to as milk sugar) is a sugar that 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.
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[edit] Chemistry
Lactose is a disaccharide that consists of β-D-galactose and α/β-D-glucose fragments bonded through a β1-4 glycosidic linkage. As it gives free radicals by mechanochemistry, it is possible to use lactose to follow by ESR (Electron Spin Resonance) the energy used during a milling process.[1]
[edit] 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.[2]
[edit] Digestion of Lactose (Catabolism)
Infant mammals nurse on their mothers to drink milk, which is rich in the carbohydrate lactose. The intestinal villi secrete an enzyme called lactase (β-D-galactosidase) to digest it. This enzyme cleaves the lactose molecule into its two subunits, the simple sugars glucose and galactose, which can be absorbed.
Since lactose occurs mostly in milk, in most mammals the production of lactase gradually decreases with maturity due to a lack of constant consumption.
Many people with ancestry in Europe, the Middle East, India, and parts of East Africa maintain lactase production into adulthood. In many of these areas, milk from mammals such as cattle, goats, and sheep is used as a large source of 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.
People who are not lactose tolerant may suffer uncomfortable or socially unacceptable symptoms of too much lactose consumption. In these people, lactose is not broken down and provides food for gas-producing gut flora. This can lead to bloating, flatulence, and other gastrointestinal symptoms.[3]
[edit] References
- ^ Baron M., Chamayou, A., Marchioro L., Raffi J., Adv. Powder Technol., 2005, 16, 3, 199-212.
- ^ Machado, José J.B.; João A. Coutinho, Eugénia A. Macedo (20001) (PDF). Solid–liquid equilibrium of a-lactose in ethanol/water. Fluid Phase Equilibria. http://path.web.ua.pt/file/FPE%20(2000)%20173%20121.pdf. Retrieved on 2007-12-05.
- ^ Nicholas Wade (December 10, 2006). "Study Detects Recent Instance of Human Evolution". The New York Times. http://www.nytimes.com/2006/12/10/science/10cnd-evolve.html?. Retrieved on 2007-12-05.
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