lactose

(lăk'tōs')

1. A disaccharide, C₁₂H₂₂O₁₁, found in milk, that may be hydrolyzed to yield glucose and galactose.
2. A white crystalline substance obtained from whey and used in infant foods, bakery products, confections, and pharmaceuticals as a diluent and excipient. Also called milk sugar.

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Milk sugar or 4-O-β-D-galactopyranosyl-D-glucose. This reducing disaccharide is obtained as the α-D anomer (see formula, where the asterisk indicates a reducing group); the melting point is 202°C (396°F). Lactose is found in the milk of

The carbohydrate of milk, sometimes called milk sugar. A disaccharide of glucose and galactose. Used pharmaceutically as a tablet filler and as a medium for growth of micro-organisms. The fermentation of lactose to lactic acid by bacteria is responsible for the souring of milk. Ordinary lactose is α-lactose, which is 16% as sweet as sucrose; if crystallized above 93 °C, it is converted to the β-form which is more soluble and sweeter.

A sugar found in milk. It is a disaccharide made by the combination of galactose and glucose. Milk goes sour because the lactose is converted by bacteria into lactic acid. Lactose is an energy-rich food but some people suffer from lactose intolerance in which the consumption of milk (or other foods containing lactose) causes cramps, flatulence, and diarrhoea.

Lactose intolerance is due to a deficiency in the production of lactase, an enzyme that digests lactose into glucose and galactose. It most often affects people who consume few milk products, but since lactase production tends to reduce with age, a large proportion of the population may suffer some degree of lactose intolerance as they grow older. In fact, most ethnic groups (apart from Caucasians) do not retain lactase past adolescence so most adults are lactose intolerant. A few sufferers can still eat some fermented dairy products, such as buttermilk and yoghurt, or they may be able to obtain lactase-treated products. Others may have to avoid dairy products altogether. These people have to find alternative sources of the nutrients, such as calcium and riboflavin, that they would otherwise obtain from milk or its products.

[LAK-tohs] This sugar occurs naturally in milk and is also called milk sugar. It's the least sweet of all the natural sugars and is used commercially in foods such as baby formulas and candies.

A disaccharide sugar made from galactose and glucose; milk sugar. Although lactose is potentially a rich source of energy, many people suffer from lactose intolerance because they lack the enzyme (lactase) required to digest it.

A sugar derived from milk, which on hydrolysis yields glucose and galactose.

• l. digestion test — oral test of foal's ability to digest milk sugar.
• l. intolerance — inability to digest lactose in the diet because of the lack of the enzyme lactase in the small intestine. Clinical consequences are intestinal discomfort and diarrhea.
• l. tolerance test — a monitor of intestinal epithelial damage, similar to the starch digestion test. The test measures the rise in blood glucose at timed intervals after oral administration of lactose; essentially a test of disaccharidase efficiency of the gut.

A disaccharide found in the milk of all mammals. Lactose is used as a component of formulas for infants; it is also used as a laxative and a diuretic.

• Drug Names and Forms - milk sugar: white lactose crystals for cutting cocaine or heroin

Lactose (Milk sugar)
IUPAC name β-D-galactopyranosyl-(1→4)-D-glucose
Other names Milk sugar 4-O-β-D-galactopyranosyl-D-glucose
Identifiers
CAS number	63-42-3 Y
PubChem	6134
ChemSpider	5904 Y
UNII	J2B2A4N98G N
EC-number	200-559-2
ChEBI	CHEBI:36218 N
ChEMBL	CHEMBL1159651 N
Jmol-3D images	Image 1
SMILES 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
InChI 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 Y Key: GUBGYTABKSRVRQ-DCSYEGIMSA-N Y 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
Properties
Molecular formula	C12H22O11
Molar mass	342.30 g/mol
Appearance	white solid
Density	1.525 g/cm3
Melting point	202.8 °C[1]
Boiling point	668.9 °C[1]
Solubility in water	21.6 g/100 mL[2]
Thermochemistry
Std enthalpy of combustion ΔcHo298	5652 kJ/mol, 1351 kcal/mol, 16.5 kJ/g, 3.94 kcal/g
Hazards
EU Index	not listed
Flash point	357.8 °C[1]
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk (by weight), although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from lac or lactis, the Latin word for milk, plus the -ose ending used to name sugars. It has a formula of C₁₂H₂₂O₁₁.

Contents 1 History 2 Structure and reactions 3 Isolation 4 Catabolism 5 Applications 6 See also 7 References

History

Lactose was discovered in milk in 1619 by Fabriccio Bartoletti, and identified as a sugar in 1780 by Carl Wilhelm Scheele.^[3]

Structure and reactions

The molecular structure of α-lactose, as determined by X-ray crystallography.

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 anomeric form of the glucopyranose ring alone.

Lactose is hydrolysed to glucose and galactose, isomerised in alkaline solution to lactulose, and catalytically hydrogenated to the corresponding polyhydric alcohol, lactitol.^[3]

Isolation

Several million tons are produced annually as a by-product of the dairy industry. Whey is made of up 6.5% solids of which 4.8% is lactose that may be purified by crystallisation.^[4] Whey or milk plasma is the liquid remaining after milk is curdled and strained, for example in the production of cheese. Lactose makes up about 2-8% of milk by weight. Lactose is purified from whey by adding ethanol. Since it is insoluble in ethanol, lactose precipitates in about 65% yield.^[5]

Catabolism

Main article: Lactose intolerance

Infant mammals nurse on their mothers to drink milk, which is rich in lactose. The intestinal villi secrete the 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, West Asia, 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.^[6] By descent, more than 70% of western Europeans can drink milk as adults, compared with less than 30% of people from areas of Africa, eastern and south-eastern Asia and Oceania.^[7] In people who are lactose intolerant, lactose is not broken down and provides food for gas-producing gut flora, which can lead to diarrhoea, bloating, flatulence, and other gastrointestinal symptoms.

Applications

Food industry applications, both of pure lactose and lactose-containing dairy by-products, have markedly increased since the 1960s. For example, its bland flavour has lent to its use as a carrier and stabiliser of aromas and pharmaceutical products. Purified lactose can also be purchased, as high calorie diet additive.^[8]

Lactose is not fermented by baker's yeast during brewing, which may be used to advantage.^[3] For example, lactose may be used to sweeten stout beer; the resulting beer is usually called a milk stout or a cream stout.

Another major use of lactose is in the pharmaceutical industry. Lactose is added to pills as a filler because of its physical properties (i.e., compressibility) and low price. For similar reasons it can be used to dilute heroin.

See also

• Nectar
• Sugar
• Other types of sugar:
  • Monosaccharide
    • Galactose
    • Fructose
    • Glucose
    • Ribose
    • Xylose
  • Disaccharide
    • Maltose
    • Sucrose

• Sugars in wine

References

1. ^ ^{a b c} Anonymous. Sigma Aldrich. Lactose Product. http://www.sigmaaldrich.com/catalog/ProductDetail.do?lang=en&N4=17814%7CFLUKA&N5=SEARCH_CONCAT_PNO%7CBRAND_KEY&F=SPEC St. Louis MO.
2. ^ 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.Machado, José J. B.; Coutinho, João A.; Macedo, Eugénia A. (2001), "Solid–liquid equilibrium of α-lactose in ethanol/water", Fluid Phase Equilibria 173 (1): 121–34, doi:10.1016/S0378-3812(00)00388-5, http://path.web.ua.pt/file/FPE%20(2000)%20173%20121.pdf . ds
3. ^ ^{a b c} Linko, P (1982), "Lactose and Lactitol", in Birch, G.G. & Parker, K.J, Nutritive Sweeteners, London & New Jersey: Applied Science Publishers, pp. 109–132, ISBN 0-85334-997-5 
4. ^ Ranken, M. D.; R. C. Kill (1997), Food industries manual, Springer, p. 125, ISBN 0751404047 
5. ^ Minard, R. Introduction to Organic Laboratory Techniques: A Microscale Approach. Pavia, Lampman, Kriz & Engel, Saunders. 1990.
6. ^ Wade, Nicholas (2006-12-10), "Study Detects Recent Instance of Human Evolution", New York Times, http://www.nytimes.com/2006/12/10/science/10cnd-evolve.html? .
7. ^ Ridley, Matt (1999), Genome, HarperCollins, p. 193, ISBN 978-0-06-089408-5 .
8. ^ Cooper, Lenna F.; Edith M Barber, Helen S Mitchell (1947), Nutrition in Health and Disease (10th ed.), J.B. Lipincott, p. 414 

v d e Types of carbohydrates General: Aldose · Ketose · Furanose · Pyranose Geometry Cyclohexane conformation · Anomer · Mutarotation Monosaccharides Dioses Aldodiose (Glycolaldehyde) Trioses Ketotriose (Dihydroxyacetone) · Aldotriose (Glyceraldehyde) Tetroses Ketotetrose (Erythrulose) · Aldotetroses (Erythrose, Threose) Pentoses Ketopentose (Ribulose, Xylulose) Aldopentose (Ribose, Arabinose, Xylose, Lyxose) Deoxy sugar (Deoxyribose) Hexoses Ketohexose (Psicose, Fructose, Sorbose, Tagatose) Aldohexose (Allose, Altrose, Glucose, Mannose, Gulose, Idose, Galactose, Talose) Deoxy sugar (Fucose, Fuculose, Rhamnose) Heptoses Ketoheptose (Sedoheptulose, Mannoheptulose) >7 Octose · Nonose (Neuraminic acid) Multiple Disaccharides Sucrose · Lactose · Maltose · Trehalose · Turanose · Cellobiose Trisaccharides Raffinose · Melezitose · Maltotriose Tetrasaccharides Acarbose · Stachyose Other oligosaccharides Fructooligosaccharide (FOS) · Galactooligosaccharides (GOS) · Mannan-oligosaccharides (MOS) · Isomaltooligosaccharide (IMO) Polysaccharides Glucose/Glucan: Glycogen · Starch (Amylose, Amylopectin) · Cellulose · Dextrin/Dextran · Beta-glucan (Zymosan, Lentinan, Sizofiran) · Maltodextrin Fructose/Fructan: Inulin · Levan beta 2→6 Mannose/Mannan Galactose/Galactan N-Acetylglucosamine: Chitin biochemical families: proteins (amino acids/intermediates) · nucleic acids (constituents/intermediates) · carbohydrates (glycoproteins, alcohols, glycosides) lipids (fatty acids/intermediates, phospholipids, steroids, sphingolipids, eicosanoids) · tetrapyrroles/intermediates

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Dansk (Danish)
n. - laktose, mælkesukker

Nederlands (Dutch)
lactose (melksuiker)

Français (French)
n. - lactose

Deutsch (German)
n. - (Chem.) Lactose, Milchzucker

Ελληνική (Greek)
n. - λακτόζη, γαλακτοσάκχαρο

Italiano (Italian)
lattosio

Português (Portuguese)
n. - lactose (f) (Quím.)

Русский (Russian)
лактоза

Español (Spanish)
n. - lactosa

Svenska (Swedish)
n. - laktos, mjölksocker

中文（简体）(Chinese (Simplified))
乳糖

中文（繁體）(Chinese (Traditional))
n. - 乳糖

한국어 (Korean)
n. - 유당

日本語 (Japanese)
n. - ラクトース

العربيه (Arabic)
‏(الاسم) اللكتوز, سكر اللبن‏

עברית (Hebrew)
n. - ‮סוכר חלב, לקטוז‬

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