Lactose

Source: Wikipedia, the free encyclopedia.
Lactose
Names
IUPAC name
β-D-Galactopyranosyl-(1→4)-D-glucose
Systematic IUPAC name
(2R,3R,4S,5R,6S)-2-(Hydroxymethyl)-6-{[(2R,3S,4R,5R,6R)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxy}oxane-3,4,5-triol
Other names
Milk sugar
Lactobiose
4-O-β-D-Galactopyranosyl-D-glucose
Identifiers
3D model (
JSmol
)
90841
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.000.509 Edit this at Wikidata
EC Number
  • 200-559-2
342369
KEGG
UNII
  • InChI=1S/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5+,6+,7-,8-,9-,10-,11-,12+/m1/s1 checkY
    Key: GUBGYTABKSRVRQ-DCSYEGIMSA-N checkY
  • InChI=1/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5+,6+,7-,8-,9-,10-,11-,12+/m1/s1
    Key: GUBGYTABKSRVRQ-DCSYEGIMBP
  • C([C@@H]1[C@@H]([C@@H]([C@H]([C@@H](O1)O[C@@H]2[C@H](O[C@H]([C@@H]([C@H]2O)O)O)CO)O)O)O)O
Properties
C12H22O11
Molar mass 342.297 g·mol−1
Appearance White solid
Density 1.525 g/cm3
Melting point 252 °C (anhydrous)[1]
202 °C (monohydrate)[1]
195 g/L[2][3]
+55.4° (anhydrous)
+52.3° (monohydrate)
Thermochemistry
Std enthalpy of
combustion
(ΔcH⦵298)
 5652 kJ/mol, 1351 kcal/mol, 16.5 kJ/g, 3.94 kcal/g
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
0
0
Flash point 357.8 °C (676.0 °F; 631.0 K)[4]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Lactose, or milk sugar, is a

molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from lact (gen. lactis), the Latin word for milk, plus the suffix -ose used to name sugars. The compound is a white, water-soluble, non-hygroscopic solid with a mildly sweet taste. It is used in the food industry.[5]

Structure and reactions

The molecular structure of α-lactose, as determined by X-ray crystallography.
Lactose crystals, viewed under polarized light

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 have only the β-pyranose form: hence α-lactose and β-lactose refer to the anomeric form of the glucopyranose ring alone. Detection reactions for lactose are the Woehlk-

dairy products such as whole milk, lactose free milk, yogurt, buttermilk, coffee creamer, sour cream, kefir, etc.[8]

Lactose is

polyhydric alcohol, lactitol.[9]
Lactulose is a commercial product, used for treatment of constipation.

Occurrence and isolation

Lactose comprises about 2–8% of milk by weight. Several million tons are produced annually as a by-product of the

dairy industry
.

infant nutrition and sports nutrition while the permeate can be evaporated to 60–65% solids and crystallized while cooling.[11] Lactose can also be isolated by dilution of whey with ethanol.[12]

Dairy products such as yogurt and cheese contain very little lactose. This is because the bacteria used to make these products breaks down lactose through the use of lactase.

Metabolism

See also: Lactose intolerance and Lactase persistence

Infant mammals nurse on their mothers to drink milk, which is rich in lactose. The intestinal villi secrete the enzyme 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 weaning; the removal of lactose from the diet removes the metabolic pressure to continue to produce lactase for its digestion.

Many people with ancestry in

gut flora
, which can lead to diarrhea, bloating, flatulence, and other gastrointestinal symptoms.

Biological properties

The sweetness of lactose is 0.2 to 0.4, relative to 1.0 for sucrose.[15] For comparison, the sweetness of glucose is 0.6 to 0.7, of fructose is 1.3, of galactose is 0.5 to 0.7, of maltose is 0.4 to 0.5, of sorbose is 0.4, and of xylose is 0.6 to 0.7.[15]

When lactose is completely digested in the

intestines, the caloric value of lactose ranges from 2 to 4 kcal/g.[15] Undigested lactose acts as dietary fiber.[15] It also has positive effects on absorption of minerals, such as calcium and magnesium.[15]

The glycemic index of lactose is 46 to 65.[15][16] 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.[15][16]

Lactose has relatively low

cariogenicity among sugars.[17][15] This is because it is not a substrate for dental plaque formation and it is not rapidly fermented by oral bacteria.[17][15] The buffering capacity of milk also reduces the cariogenicity of lactose.[15]

Applications

Its mild flavor and easy handling properties have led to its use as a carrier and stabiliser of aromas and pharmaceutical products.[5] Lactose is not added directly to many foods, because its solubility is less than that of other sugars commonly used in food. Infant formula is a notable exception, where the addition of lactose is necessary to match the composition of human milk.

Lactose is not fermented by most

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.[18]

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.[

example needed][5] For similar reasons, it can be used to dilute illicit drugs such as cocaine or heroin.[19]

History

The first crude isolation of lactose, by Italian physician Fabrizio Bartoletti (1576–1630), was published in 1633.[20] 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.[21] In 1715, Testi's procedure for making milk sugar was published by Antonio Vallisneri.[22] Lactose was identified as a sugar in 1780 by Carl Wilhelm Scheele.[23][9]

In 1812, Heinrich Vogel (1778–1867) recognized that glucose was a product of hydrolyzing lactose.[24] In 1856, Louis Pasteur crystallized the other component of lactose, galactose.[25] By 1894, Emil Fischer had established the configurations of the component sugars.[26]

Lactose was named by the French chemist Jean Baptiste André Dumas (1800–1884) in 1843.[27] In 1856, Pasteur named galactose "lactose".[28] In 1860, Marcellin Berthelot renamed it "galactose", and transferred the name "lactose" to what is now called lactose.[29] It has a formula of C12H22O11 and the hydrate formula C12H22O11·H2O, making it an isomer of sucrose.

See also

References

  1. ^
    ISBN 978-0-8493-3829-8
    .
  2. ^ "D-Lactose".
  3. doi:10.1016/S0378-3812(00)00388-5
    . ds
  4. ^ Sigma Aldrich
  5. ^
    ISBN 978-3-527-30673-2
    .
  6. doi:10.1002/chemv.201800002
    .
  7. ISSN 0003-2654
    .
  8. S2CID 208714341
    .
  9. ^
    ISBN 978-0-85334-997-6
  10. ISBN 978-0-7514-0404-3
  11. PMID 24517206
    , DOI is open access
  12. ISBN 0-03-014813-8
  13. ^ Wade, Nicholas (2006-12-10), "Study Detects Recent Instance of Human Evolution", New York Times.
  14. ISBN 978-0-06-089408-5
    .
  15. ^
    S2CID 10346203. Archived from the original
    (PDF) on Mar 2, 2019.
  16. ^
    S2CID 14574754
    .
  17. ^
    ISBN 978-1-4200-0431-1
    .
  18. ^ Ling, Charles (2008), Whey to Ethanol: A Biofuel Role for Dairy Cooperatives? (PDF), United States Department of Agriculture Rural Development.
  19. PMID 32141480
    .
  20. Sendivogius
    .] 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. Archived 2018-11-09 at the Wayback Machine From page 163: "Undd Bertholetus praeparat ex sero lactis remedium, quod vocat mannam S. [alchemical symbol for salt, salem] 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: this is a mistake; the preparation appeared in Bartoletti's Methodus in dyspnoeam … ], p. 400. This is the preparation: … )
  21. ^ Lodovico Testi, De novo Saccharo Lactis [On the new milk sugar] (Venice, (Italy): Hertz, 1700).
  22. ^ 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.
  23. ^ See:
    • Carl Wilhelm Scheele (1780) "Om Mjölk och dess syra" (About milk and its acid), Kongliga Vetenskaps Academiens Nya Handlingar (New Proceedings of the Royal Academy of Science), 1 : 116–124. From page 116: "Det år bekant, at Ko-mjölk innehåller Smör, Ost, Mjölk-såcker, … " (It is known, that cow's milk contains butter, cheese, milk-sugar, … )
    • Carl Wilhelm Scheele (1780) "Om Mjölk-Såcker-Syra" (On milk-sugar acid), Kongliga Vetenskaps Academiens Nya Handlingar (New Proceedings of the Royal Academy of Science), 1 : 269–275. From pages 269–270: "Mjölk-Såcker år et sal essentiale, som uti Mjölken finnes uplöst, och som, för dess sötaktiga smak skull, fått namn af såcker." (Milk sugar is an essential salt, which is found dissolved in milk, and which, on account of its sweet taste, has the name of "sugar".)
  24. ^ See:
  25. ^ Pasteur (1856) "Note sur le sucre de lait" (Note on milk sugar), Comptes rendus, 42 : 347–351.
  26. ^ Fischer determined the configuration of glucose in:
    • Emil Fischer (1891) "Ueber die Configuration des Traubenzuckers und seiner Isomeren" (On the configuration of grape sugar and its isomers), Berichte der Deutschen Chemischen Gesellschaft, 24 : 1836–1845.
    • Emil Fischer (1891) "Ueber die Configuration des Traubenzuckers und seiner Isomeren. II" (On the configuration of grape sugar and its isomers), Berichte der Deutschen Chemischen Gesellschaft, 24 : 2683–2687.
    Fischer established the configuration of galactose in:
    • Emil Fischer and Robert S. Morrell (1894) "Ueber die Configuration der Rhamnose und Galactose" (On the configuration of rhamnose and galactose), Berichte der Deutschen chemischen Gesellschaft zu Berlin, 27 : 382–394. The configuration of galactose appears on page 385.
  27. ^ Dumas, Traité de Chimie, Appliquée aux Arts, volume 6 (Paris, France: Bechet Jeune, 1843), p. 293.
  28. ^ 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.)
  29. ^ Marcellin Berthelot, Chimie organique fondée sur la synthèse [Organic chemistry based on synthesis] (Paris, France: Mallet-Bachelier, 1860), vol. 2, pp. 248–249 and pp. 268–270.

External links

  • Media related to Lactose at Wikimedia Commons
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