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Lactose, or milk sugar, is a disaccharide composed of galactose and glucose and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from (Genitive case. ), the Latin word for milk, plus the suffix -ose used to name sugars. The compound is a white, water-soluble, non-Hygroscopy solid with a mildly sweet taste. It is used in the food industry.
Lactose is hydrolysed to glucose and galactose, isomerisation in Basicity solution to lactulose, and catalysis Hydrogenation to the corresponding polyhydric alcohol, lactitol. Lactulose is a commercial product, used for treatment of constipation.
Whey or milk plasma is the liquid remaining after milk is curdled and strained, for example in the production of cheese. Whey is made up of 6.5% solids, of which 4.8% is lactose, which is purified by crystallisation. Industrially, lactose is produced from whey permeate – whey filtrated for all major . The protein fraction is used in infant nutrition and sports nutrition while the permeate can be evaporated to 60–65% solids and crystallized while cooling., DOI is open access Lactose can also be isolated by dilution of whey with ethanol.
Many people with ancestry in Europe, West Asia, South Asia, the Sahel belt in West Africa, East Africa and a few other parts of Central Africa maintain lactase production into adulthood due to selection for genes that continue lactase production. In many of these areas, milk from mammals such as cattle, goats, and sheep is used as a large source of food. It was in these regions that genes for lifelong lactase production first evolution. The genes of adult lactose tolerance have evolved independently in various ethnic groups.. By descent, more than 70% of western Europeans can digest lactose as adults, compared with less than 30% of people from areas of Africa, eastern and south-eastern Asia and Oceania.. In people who are lactose intolerant, lactose is not broken down and provides food for gas-producing gut flora, which can lead to diarrhea, bloating, flatulence, and other gastrointestinal symptoms.
When lactose is completely digested in the small intestine, its caloric value is 4 kcal/g, or the same as that of other . However, lactose is not always fully digested in the small intestine. Depending on ingested dose, combination with meals (either solid or liquid), and lactase activity in the , the caloric value of lactose ranges from 2 to 4 kcal/g. Undigested lactose acts as dietary fiber. It also has positive effects on absorption of , such as calcium and magnesium.
The glycemic index of lactose is 46 to 65. For comparison, the glycemic index of glucose is 100 to 138, of sucrose is 68 to 92, of maltose is 105, and of fructose is 19 to 27.
Lactose has relatively low cariogenicity among sugars. This is because it is not a substrate for dental plaque formation and it is not rapidly fermentation by mouth bacteria. The buffering capacity of milk also reduces the cariogenicity of lactose.
One of the undesirable properties of lactose utilization is its low solubility, which can result in crystallization, giving a gritty and sandy mouthfeel in the final product. Usually, in supersaturated solution, sugars tend to crystallize, also forming big agglomerates, depending on the process condition.
Lactose is not fermented by most yeast during brewing, which may be used to advantage. For example, lactose may be used to sweeten stout beer; the resulting beer is usually called a milk stout or a cream stout.
Yeast belonging to the genus Kluyveromyces have a unique industrial application, as they are capable of fermenting lactose for ethanol production. Surplus lactose from the whey by-product of dairy operations is a potential source of alternative energy..
Another significant lactose use is in the pharmaceutical industry. Lactose is added to tablet and capsule drug products as an ingredient because of its physical and functional properties (examples are atorvastatin, levocetirizine or thiamazole among many others). For similar reasons, it can be used to dilute illicit drugs such as cocaine or heroin.
In 1812, Heinrich Vogel (1778–1867) recognized that glucose was a product of hydrolyzing lactose.See:
Lactose was named by the French chemist Jean Baptiste André Dumas (1800–1884) in 1843.Dumas, Traité de Chimie, Appliquée aux Arts, volume 6 (Paris, France: Bechet Jeune, 1843), p. 293. In 1856, Pasteur named galactose "lactose".Pasteur (1856) "Note sur le sucre de lait" (Note on milk sugar), Comptes rendus, 42 : 347–351. From page 348: "Je propose de le nommer lactose ." (I propose to name it lactose.) In 1860, Marcellin Berthelot renamed it "galactose", and transferred the name "lactose" to what is now called lactose.Marcellin Berthelot, Chimie organique fondée sur la synthèse Organic (Paris, France: Mallet-Bachelier, 1860), vol. 2, pp. 248–249 and pp. 268–270. It has a formula of C12H22O11 and the hydrate formula C12H22O11·H2O, making it an isomer of sucrose.
History
The first crude isolation of lactose, by Italian physician Fabrizio Bartoletti (1576–1630), was published in 1633.Fabrizio Bartoletti, Methodus in dyspnoeam ... Procedure, (Bologna ("Bononia"), (Italy): Nicolò Tebaldini for the heirs of Evangelista Dozza, 1633), p. 400. From page 400: "italic=no seri hæc. Destilla leni balnei calore serum lactis, donec in fundo vasis butyracea fœx subsideat, cui hærebit salina quædam substantia subalbida. Hanc curiose segrega, est enim sal seri essentiale; seu nitrum, cujus causa nitrosum dicitut serum, huicque tota abstergedi vis inest. Solve in aqua propria, & coagula. Opus repete, donec seri cremorem habeas sapore omnino mannam referentem." (This is the manna of whey. Note: Gently distill whey via a heat bath until the buttery scum settles to the bottom of the vessel, to which substance some whitish salt i.e., attaches. This curious substance separated, is truly the essential salt of whey; or, on account of which nitre, is called "nitre of whey", and all life force is in this that will be expelled. Note: Dissolve it in its own water and coagulate. Repeat the operation until you have cream of whey, recalling, by its taste, only manna.)
In 1688, the German physician Michael Ettmüller (1644–1683) reprinted Bartoletti's preparation. See: Ettmüller, Michael, Opera Omnia ... (Frankfurt am Main ("Francofurtum ad Moenum"), Germany: Johann David Zunner, 1688), book 2, page 163. From page 163: "Undd Bertholetus praeparat ex sero lactis remedium, quod vocat mannam S. alchemical seri lactis vid. in Encyclopaed . p. 400. Praeparatio est haec: ... " (Whence Bartoletti prepared from milk whey a medicine, which he called manna or salt of milk whey; see in his Encyclopedia note:, p. 400. This is the preparation: ... ) 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.Lodovico Testi, De novo Saccharo Lactis On (Venice, (Italy): Hertz, 1700). In 1715, Testi's procedure for making milk sugar was published by Antonio Vallisneri.Ludovico Testi (1715) "Saccharum lactis" (Milk sugar), Academiae Caesareo-Leopoldinae naturae curiosorum ephemerides, ... , 3 : 69–79. The procedure was also published in Giornale de' letterati d'Italia in 1715. Lactose was identified as a sugar in 1780 by Carl Wilhelm Scheele.See:
In 1856, Louis Pasteur crystallized the other component of lactose, galactose.Pasteur (1856) "Note sur le sucre de lait" (Note on milk sugar), Comptes rendus, 42 : 347–351. By 1894, Emil Fischer had established the configurations of the component sugars.Fischer determined the configuration of glucose in:
See also
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