View source for Lactose

{{short description|Carbohydrate}}
{{Chembox
| Verifiedfields = changed
| Watchedfields  = changed
| verifiedrevid  = 477497006
| Name           = Lactose
| ImageFile_Ref  = {{chemboximage|correct|??}}
| ImageFile      = Beta-D-Lactose.svg
| ImageSize      = 200px
| ImageClass     = skin-invert-image
| IUPACName      = β-{{sm|d}}-Galactopyranosyl-(1→4)-α-{{sm|d}}-glucopyranose<br>
4-''O''-β-{{sm|d}}-Galactopyranosyl-α-{{sm|d}}-glucopyranose
| SystematicName = (2''R'',3''R'',4''S'',5''R'',6''S'')-2-(Hydroxymethyl)-6-<nowiki/>{[(2''R'',3''S'',4''R'',5''R'',6''R'')-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxy}oxane-3,4,5-triol
| OtherNames     = Milk sugar<br />Lactobiose<br />4-''O''-β-<small>D</small>-Galactopyranosyl-<small>D</small>-glucose
| Section1       = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 5904
| 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
| InChIKey = GUBGYTABKSRVRQ-DCSYEGIMBP
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 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
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = GUBGYTABKSRVRQ-DCSYEGIMSA-N
| CASNo = 63-42-3
| CASNo_Ref = {{cascite|correct|CAS}}
| EC_number = 200-559-2
| KEGG = C01970
| PubChem = 6134
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 417016
| Gmelin = 342369
| Beilstein = 90841
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 3SY5LH9PMK
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 36218
| 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
}}
| Section2       = {{Chembox Properties
| C=12 | H=22 | O=11
| Appearance = White solid
| Density = 1.525{{nbsp}}g/cm<sup>3</sup>
| MeltingPt = 252&nbsp;°C (anhydrous)<ref name="DoC">{{cite book | author=Peter M. Collins | title=Dictionary of Carbohydrates | edition=2nd | year=2006 | publisher=Chapman & Hall/CRC | location=Boca Raton | isbn=978-0-8493-3829-8 | page=677}}</ref> <br /> 202 °C (monohydrate)<ref name="DoC"/>
| MeltingPt_ref =
| Solubility = 195{{nbsp}}g/L<ref name=PubChem>{{Cite web | url=https://pubchem.ncbi.nlm.nih.gov/compound/440995#section=Experimental-Properties | title=D-Lactose}}</ref><ref>The solubility of lactose in water is 189.049&nbsp;g at 25&nbsp;°C, 251.484&nbsp;g at 40&nbsp;°C and 372.149&nbsp;g at 60&nbsp;°C per kg solution. Its solubility in [[ethanol]] is 0.111&nbsp;g at 40&nbsp;°C and 0.270&nbsp;g at 60&nbsp;°C per kg solution.{{citation | year = 2001 | last1 = Machado | first1 = José J. B. | first2 = João A. | last2 = Coutinho | first3 = Eugénia A. | last3 = Macedo | title = Solid–liquid equilibrium of α-lactose in ethanol/water | url = http://path.web.ua.pt/file/FPE%20(2000)%20173%20121.pdf | journal = Fluid Phase Equilibria | volume = 173 | issue = 1 | pages = 121–34 | doi = 10.1016/S0378-3812(00)00388-5}}.
ds</ref>
| SpecRotation = +55.4° (anhydrous)<br />+52.3° (monohydrate)
  }}
| Section4       = {{Chembox Thermochemistry| DeltaHc = 5652{{nbsp}}kJ/mol, 1351{{nbsp}}kcal/mol, 16.5{{nbsp}}kJ/g, 3.94{{nbsp}}kcal/g}}
| Section7       = {{Chembox Hazards
| FlashPtC = 357.8
| FlashPt_ref = <ref name=Ald>[http://www.sigmaaldrich.com/catalog/product/sial/17814?lang=en&region=US Sigma Aldrich]</ref>
| AutoignitionPtC =
| NFPA-H = 0
| NFPA-F = 0
| NFPA-R = 0
  }}
}}

'''Lactose''' is a [[disaccharide]] composed of [[galactose]] and [[glucose]] and has the [[molecular formula]] C<sub>12</sub>H<sub>22</sub>O<sub>11</sub>. Lactose makes up around 2–8% of [[milk]] (by mass). The name comes from {{wikt-lang|la|lac}} ([[Genitive case|gen]].&nbsp;{{wikt-lang|la|lactis}}), the [[Latin]] word for milk, plus the suffix ''[[-ose]]'' used to name sugars. The compound is a white, [[water-soluble]], non-[[Hygroscopy|hygroscopic]] solid with a mildly sweet taste. It is used in the food industry.<ref name=Ull>{{cite encyclopedia|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|author=Gerrit M. Westhoff |author2=Ben F.M. Kuster |author3=Michiel C. Heslinga |author4=Hendrik Pluim |author5=Marinus Verhage |year=2014|pages=1–9|doi= 10.1002/14356007.a15_107.pub2|publisher=Wiley-VCH|chapter=Lactose and Derivatives|isbn=978-3-527-30673-2}}</ref>

==Structure and reactions==
[[File:Alpha-lactose-from-xtal-3D-balls.png|thumb|left|The molecular structure of α-lactose, as determined by [[X-ray crystallography]].]]
Lactose is a [[disaccharide]] composed of [[galactose]] and [[glucose]], which form a β-1→4 [[Glycosidic bond|glycosidic]] linkage. Its [[systematic name]] is β-<small>D</small>-galactopyranosyl-(1→4)-<small>D</small>-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 [[anomer]]ic form of the glucopyranose ring alone. Detection reactions for lactose are the [[Alfred Wöhlk|Wöhlk]]<ref>{{Cite journal |last1=Ruppersberg |first1=Klaus |last2=Blankenburg |first2=Janet |date=2018 |title=150 Years Alfred Wöhlk |url=http://www.chemistryviews.org/details/education/10821368/150_Years_Alfred_Wohlk.html |journal=ChemViews |doi=10.1002/chemv.201800002|url-access=subscription }}</ref> and [[William Fearon|Fearon]] tests.<ref>{{Cite journal |last=Fearon |first=W. R. |date=1942 |title=The detection of lactose and maltose by means of methylamine |url=http://xlink.rsc.org/?DOI=an9426700130 |journal=The Analyst |language=en |volume=67 |issue=793 |page=130 |doi=10.1039/an9426700130 |bibcode=1942Ana....67..130F |issn=0003-2654|url-access=subscription }}</ref> They can be used to detect the different lactose content of [[dairy products]] such as [[whole milk]], [[Lactose free diet|lactose free milk]], [[yogurt]], [[buttermilk]], [[coffee creamer]], [[sour cream]], [[kefir]], etc.<ref>{{Cite journal |last1=Ruppersberg |first1=Klaus |last2=Herzog |first2=Stefanie |last3=Kussler |first3=Manfred W. |last4=Parchmann |first4=Ilka |date=2019-10-17 |title=How to visualize the different lactose content of dairy products by Fearon's test and Woehlk test in classroom experiments and a new approach to the mechanisms and formulae of the mysterious red dyes |journal=[[Chemistry Teacher International]] |volume=2 |issue=2 |doi=10.1515/cti-2019-0008 |issn=2569-3263 |s2cid=208714341 |doi-access=free}}</ref>

Lactose is [[hydrolysed]] to glucose and galactose, [[isomerisation|isomerised]] in [[Basicity|alkaline]] solution to [[lactulose]], and [[catalysis|catalytically]] [[Hydrogenation|hydrogenated]] to the corresponding [[polyhydric alcohol]], [[lactitol]].<ref name="Linko1981"/> Lactulose is a commercial product, used for treatment of [[constipation]].<ref>{{Citation |last=Hawrelak |first=Jason A. |title=104 - Prebiotics, Synbiotics, and Colonic Foods |date=2020-01-01 |work=Textbook of Natural Medicine (Fifth Edition) |pages=797–808.e4 |editor-last=Pizzorno |editor-first=Joseph E. |url=https://linkinghub.elsevier.com/retrieve/pii/B9780323430449001047 |access-date=2025-02-15 |place=St. Louis (MO) |publisher=Churchill Livingstone |doi=10.1016/b978-0-323-43044-9.00104-7 |isbn=978-0-323-52342-4 |editor2-last=Murray |editor2-first=Michael T.|url-access=subscription }}</ref>

==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]].{{cn|date=May 2024}}

[[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.<ref>{{Citation |last1=Ranken |first1=M. D. |title=Food industries manual |url=https://archive.org/details/foodindustriesma0000unse |page=125 |year=1997 |publisher=Springer |isbn=978-0-7514-0404-3 |last2=Kill |first2=R. C.}}</ref> Industrially, lactose is produced from whey permeate – whey filtrated for all major [[protein]]s. 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.<ref>{{citation |last1=Wong |first1=S. Y. |title=Crystallization in lactose refining-a review |journal=[[Journal of Food Science]] |volume=79 |issue=3 |pages=R257–72 |year=2014 |doi=10.1111/1750-3841.12349 |pmid=24517206 |last2=Hartel |first2=R. W.|doi-access=free }}, DOI is open access</ref> Lactose can also be isolated by dilution of whey with [[ethanol]].<ref>{{citation |title=Introduction to Organic Laboratory Techniques: A Microscale Approach |first1=Donald L. |last1=Pavia |first2=Gary M. |last2=Lampman |first3=George S. |last3=Kriz |publisher=Saunders |year=1990 |isbn=0-03-014813-8 }}</ref>

==Metabolism==
{{See also|Lactose intolerance|Lactase persistence}}

Infant [[mammal]]s nurse on their mothers to drink milk, which is rich in lactose. The [[Intestinal villus|intestinal villi]] secrete the [[enzyme]] [[lactase]] (β-D-galactosidase) to digest it. This enzyme cleaves the lactose molecule into its two subunits, the simple [[sugar]]s 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.<ref>{{Citation |last1=Balaresque |first1=P. |title=Chapter Nine - Human Phenotypic Diversity: An Evolutionary Perspective |date=2016-01-01 |journal=Current Topics in Developmental Biology |volume=119 |pages=349–390 |editor-last=Orgogozo |editor-first=Virginie |url=https://linkinghub.elsevier.com/retrieve/pii/S0070215316300011 |access-date=2025-02-15 |series=Genes and Evolution |publisher=Academic Press |doi=10.1016/bs.ctdb.2016.02.001 |last2=King |first2=T. E.|pmid=27282030 |url-access=subscription }}</ref><ref>{{Cite journal |last1=Gerbault |first1=Pascale |last2=Liebert |first2=Anke |last3=Itan |first3=Yuval |last4=Powell |first4=Adam |last5=Currat |first5=Mathias |last6=Burger |first6=Joachim |last7=Swallow |first7=Dallas M. |last8=Thomas |first8=Mark G. |date=2011-03-27 |title=Evolution of lactase persistence: an example of human niche construction |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=366 |issue=1566 |pages=863–877 |doi=10.1098/rstb.2010.0268 |issn=0962-8436 |pmc=3048992 |pmid=21320900}}</ref>

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|evolved]].<ref>{{Cite journal |last1=Itan |first1=Yuval |last2=Powell |first2=Adam |last3=Beaumont |first3=Mark A. |last4=Burger |first4=Joachim |last5=Thomas |first5=Mark G. |date=2009-08-28 |editor-last=Tanaka |editor-first=Mark M. |title=The Origins of Lactase Persistence in Europe |journal=PLOS Computational Biology |language=en |volume=5 |issue=8 |article-number=e1000491 |doi=10.1371/journal.pcbi.1000491 |doi-access=free |issn=1553-7358 |pmc=2722739 |pmid=19714206|bibcode=2009PLSCB...5E0491I }}</ref> The genes of adult lactose tolerance have evolved independently in various ethnic groups.<ref>{{citation | first = Nicholas | last = Wade | title= Study Detects Recent Instance of Human Evolution | date = 2006-12-10 | newspaper= New York Times | url= https://www.nytimes.com/2006/12/10/science/10cnd-evolve.html?}}.</ref> 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.<ref>{{Citation |last= Ridley |first= Matt |title= Genome |publisher= [[HarperCollins]] |year= 1999 |page= 193 |isbn= 978-0-06-089408-5}}.</ref> 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.

==Biological properties==
The [[sweetness]] of lactose is 0.2 to 0.4, relative to 1.0 for [[sucrose]].<ref name="Schaafsma2008">{{cite journal |last1=Schaafsma |first1=Gertjan |year=2008 |title=Lactose and lactose derivatives as bioactive ingredients in human nutrition |url=http://pdfs.semanticscholar.org/a45b/ce8eb621c78f163ec94f6e2c5add17a624e4.pdf |journal=International Dairy Journal |volume=18 |issue=5 |pages=458–465 |doi=10.1016/j.idairyj.2007.11.013 |s2cid=10346203 |issn=0958-6946 |archive-url=https://web.archive.org/web/20190302135517/http://pdfs.semanticscholar.org/a45b/ce8eb621c78f163ec94f6e2c5add17a624e4.pdf |archive-date=Mar 2, 2019}}</ref> 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.<ref name="Schaafsma2008" />

When lactose is completely digested in the [[small intestine]], its [[caloric value]] is 4 kcal/g, or the same as that of other [[carbohydrate]]s.<ref name="Schaafsma2008" /> 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 [[intestine]]s, the caloric value of lactose ranges from 2 to 4 kcal/g.<ref name="Schaafsma2008" /> Undigested lactose acts as [[dietary fiber]]. It also has positive effects on absorption of [[mineral]]s, such as [[calcium]] and [[magnesium]].<ref name="Schaafsma2008" />

The [[glycemic index]] of lactose is 46 to 65.<ref name="BjörckLiljeberg2000">{{cite journal |last1=Björck |first1=Inger |last2=Liljeberg |first2=Helena |last3=Östman |first3=Elin |year=2000 |title=Low glycaemic-index foods |journal=British Journal of Nutrition |volume=83 |issue=S1 |pages=S149–S155 |doi=10.1017/S0007114500001094 |issn=0007-1145 |pmid=10889806 |s2cid=14574754 |doi-access=free}}</ref> 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.<ref name="Schaafsma2008" /><ref name="BjörckLiljeberg2000" />

Lactose has relatively low [[cariogenicity]] among sugars.<ref name="MillerJarvis2006">{{cite book|author1=Gregory D. Miller|author2=Judith K. Jarvis|author3=Lois D. McBean|title=Handbook of Dairy Foods and Nutrition|url=https://books.google.com/books?id=5tleQ0aLJvoC&pg=PA248|date=15 December 2006|publisher=CRC Press|isbn=978-1-4200-0431-1|pages=248–}}</ref> This is because it is not a substrate for [[dental plaque]] formation and it is not rapidly [[fermentation|fermented]] by [[mouth|oral]] [[bacteria]].<ref name="MillerJarvis2006" /> The buffering capacity of milk also reduces the cariogenicity of lactose.<ref name="Schaafsma2008" />

==Applications==
Its mild flavor and easy handling properties have led to its use as a carrier and stabiliser of aromas and pharmaceutical products.<ref name=Ull/> Lactose is not commonly added directly to food, because its low solubility can lead to a gritty mouthfeel.<ref>{{Cite journal |last1=Dominici |first1=Simona |last2=Marescotti |first2=Francesca |last3=Sanmartin |first3=Chiara |last4=Macaluso |first4=Monica |last5=Taglieri |first5=Isabella |last6=Venturi |first6=Francesca |last7=Zinnai |first7=Angela |last8=Facioni |first8=Maria Sole |date=2022-05-19 |title=Lactose: Characteristics, Food and Drug-Related Applications, and Its Possible Substitutions in Meeting the Needs of People with Lactose Intolerance |journal=Foods |language=en |volume=11 |issue=10 |page=1486 |doi=10.3390/foods11101486 |doi-access=free |issn=2304-8158 |pmc=9141425 |pmid=35627056}}</ref> [[Infant formula]] is a notable exception, where lactose is added to match the composition of human milk.<ref>{{Cite journal |last1=Slupsky |first1=Carolyn M. |last2=He |first2=Xuan |last3=Hernell |first3=Olle |last4=Andersson |first4=Yvonne |last5=Rudolph |first5=Colin |last6=Lönnerdal |first6=Bo |last7=West |first7=Christina E. |date=2017-06-16 |title=Postprandial metabolic response of breast-fed infants and infants fed lactose-free vs regular infant formula: A randomized controlled trial |journal=Scientific Reports |language=en |volume=7 |issue=1 |page=3640 |doi=10.1038/s41598-017-03975-4 |issn=2045-2322 |pmc=5473881 |pmid=28623320|bibcode=2017NatSR...7.3640S }}</ref> However, lactose-reduced formulas are increasing in popularity.<ref>{{Cite journal |last1=DiMaggio |first1=Dina M. |last2=Abersone |first2=Ilze |last3=Porto |first3=Anthony F. |date=2024 |title=Infant consumption of 100% lactose-based and reduced lactose infant formula in the United States: Review of NHANES data from 1999 to 2020 |url=https://onlinelibrary.wiley.com/doi/10.1002/jpn3.12292 |journal=Journal of Pediatric Gastroenterology and Nutrition |language=en |volume=79 |issue=5 |pages=1017–1023 |doi=10.1002/jpn3.12292 |pmid=38934419 |issn=1536-4801|url-access=subscription }}</ref>

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.<ref name=Linko1981/> 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.<ref>{{citation |last=Ling |first=Charles |title=Whey to Ethanol: A Biofuel Role for Dairy Cooperatives? |date=2008 |url=http://www.rd.usda.gov/files/RR214.pdf |archive-url=https://web.archive.org/web/20150224064134/http://www.rd.usda.gov/files/RR214.pdf |archive-date=February 24, 2015 |publisher=United States Department of Agriculture Rural Development}}.</ref>

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).<ref name=Ull/><ref>{{Cite journal |last1=Zdrojewicz |first1=Z. |last2=Zyskowska |first2=K. |last3=Wasiuk |first3=S. |date=2018 |title=Lactose in drugs and lactose intolerance – realities and myths |url=https://pimr.pl/index.php/issues/2018-vol-14-no-3/lactose-in-drugs-and-lactose-intolerance-realities-and-myths |journal=Paediatrics and Family Medicine |volume=14 |issue=3 |pages=261–266 |doi=10.15557/PiMR.2018.0027|doi-access=free }}</ref> For similar reasons, it can be used to dilute illicit drugs such as cocaine or heroin.<ref>{{Cite journal |last1=Rinaldi |first1=R. |last2=Negro |first2=F. |last3=Minutillo |first3=A. |date=2020-02-20 |title=The health threat of new synthetic opioids as adulterants of classic drugs of abuse |url=http://www.clinicaterapeutica.it/2020/171/2/05_MINUTILLO.pdf |journal=La Clinica Terapeutica |volume=171 |issue=2 |pages=107–109 |doi=10.7417/CT.2020.2198 |issn=1972-6007 |pmid=32141480}}</ref>

==History==
The first crude isolation of lactose, by Italian physician Fabrizio Bartoletti (1576–1630), was published in 1633.<ref>Fabrizio Bartoletti, ''{{Lang|la|Methodus in dyspnoeam}}'' ... [Procedure for asthma ... ],  (Bologna ("Bononia"), (Italy):  Nicolò Tebaldini for the heirs of Evangelista Dozza, 1633), [https://books.google.com/books?id=T3JEAAAAcAAJ&pg=PA399 p. 400.]  From page 400:  ''"''{{Lang|la|Manna|italic=no}}'' {{Lang|la|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:  "Manna" was the dried, sweet sap of the tree ''[[Fraxinus ornus]]''.]  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., precipitate] attaches.  This curious [substance once] 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:  "Nitre" was an alchemical concept.  It was the power of life, which gave life to otherwise inanimate matter.  See the philosophy of [[Sendivogius]].]  Dissolve it in [its] own water and coagulate.  Repeat the operation until you have cream of whey, recalling, by [its] taste, only manna.)<br />
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, [http://digital.slub-dresden.de/werkansicht/dlf/79899/913/1/cache.off page 163.] {{Webarchive|url=https://web.archive.org/web/20181109143338/http://digital.slub-dresden.de/werkansicht/dlf/79899/913/1/cache.off|date=2018-11-09}}  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: ... )</ref> In 1700, the Venetian pharmacist Lodovico Testi (1640–1707) published a booklet of testimonials to the power of milk sugar (''{{Lang|la|saccharum lactis}}'') to relieve, among other ailments, the symptoms of arthritis.<ref>Lodovico Testi, [https://books.google.com/books?id=hwM9AAAAcAAJ&pg=PP9 ''De novo Saccharo Lactis''] [On the new milk sugar] (Venice, (Italy):  Hertz, 1700).</ref> In 1715, Testi's procedure for making milk sugar was published by Antonio Vallisneri.<ref>Ludovico Testi (1715) [http://babel.hathitrust.org/cgi/pt?view=image;size=100;id=ucm.5324347611;page=root;seq=93;num=69 "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.</ref> Lactose was identified as a sugar in 1780 by [[Carl Wilhelm Scheele]].<ref>See:
* Carl Wilhelm Scheele (1780) [https://books.google.com/books?id=9N84AAAAMAAJ&pg=PA116 "Om Mjölk och dess syra"] (About milk and its acid), ''{{Lang|sv|Kongliga Vetenskaps Academiens Nya Handlingar}}'' (New Proceedings of the Royal Academy of Science), '''1''' :  116–124.  From page 116:  ''"{{Lang|sv|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) [https://books.google.com/books?id=9N84AAAAMAAJ&pg=PA269 "Om Mjölk-Såcker-Syra"] (On milk-sugar acid), ''{{Lang|sv|Kongliga Vetenskaps Academiens Nya Handlingar}}'' (New Proceedings of the Royal Academy of Science), '''1''' :  269–275.  From pages 269–270:  ''"{{Lang|sv|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".)</ref><ref name="Linko1981">{{citation |author1=Linko, P |title=Natural Sweeteners |url=https://archive.org/details/nutritivesweeten0000unse |pages=109–132 |year=1982 |editor1=Birch, G.G. |chapter=Lactose and Lactitol |place=London & New Jersey |publisher=Applied Science Publishers |isbn=978-0-85334-997-6 |editor2=Parker, K.J}}</ref>

In 1812, Heinrich Vogel (1778–1867) recognized that glucose was a product of hydrolyzing lactose.<ref>See:
*  Vogel (1812) [http://babel.hathitrust.org/cgi/pt?id=nyp.33433062722768;view=1up;seq=492 "Sur le sucre liquide d'amidon, et sur la transmutation des matières douces en sucre fermentescible"] (On the liquid sugar of starch, and on the transformation of sweet materials into fermentable sugars), ''Annales de chemie et de physique'', series 1, '''82''' :  148–164; see especially pages 156–158.
*  H. A. Vogel (1812) [https://books.google.com/books?id=yKuZAAAAIAAJ&pg=PA125 "Ueber die Verwandlung der Stärke und andrer Körper in Zucker"] (On the conversion of starches and other substances into sugar), ''Annalen der Physik'', new series, '''42''' :  123–134; see especially pages 129–131.</ref> In 1856, [[Louis Pasteur]] crystallized the other component of lactose, galactose.<ref>Pasteur (1856) [https://archive.org/stream/ComptesRendusAcademieDesSciences0042/ComptesRendusAcadmieDesSciences-Tome042-Janvier-juin1856#page/n350/mode/1up "Note sur le sucre de lait"] (Note on milk sugar), ''Comptes rendus'', '''42''' :  347–351.</ref> By 1894, [[Emil Fischer]] had established the configurations of the component sugars.<ref>Fischer determined the configuration of glucose in:
*  Emil Fischer (1891) [http://gallica.bnf.fr/ark:/12148/bpt6k90723d/f1838.image.langEN "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) [http://gallica.bnf.fr/ark:/12148/bpt6k90732c/f403.image.langEN "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.</ref>

Lactose was named by the French chemist [[Jean-Baptiste Dumas|Jean Baptiste André Dumas]] (1800–1884) in 1843.<ref>Dumas, ''Traité de Chimie, Appliquée aux Arts'', volume 6 (Paris, France:  Bechet Jeune, 1843), [https://books.google.com/books?id=zQTyoAqqQzYC&pg=PA293 p. 293.]</ref> In 1856, Pasteur named galactose "lactose".<ref>Pasteur (1856) [https://archive.org/stream/ComptesRendusAcademieDesSciences0042/ComptesRendusAcadmieDesSciences-Tome042-Janvier-juin1856#page/n350/mode/1up "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''.)</ref> In 1860, [[Marcellin Berthelot]] renamed it "galactose", and transferred the name "lactose" to what is now called lactose.<ref>Marcellin Berthelot, ''Chimie organique fondée sur la synthèse''  [Organic chemistry based on synthesis] (Paris, France:  Mallet-Bachelier, 1860), vol. 2, [https://books.google.com/books?id=7AtQYV5FlVwC&pg=PA248 pp. 248–249] and [https://books.google.com/books?id=7AtQYV5FlVwC&pg=PA268 pp. 268–270.]</ref> It has a formula of {{chem2|C12H22O11}} and the hydrate formula {{chem2|C12H22O11·H2O}}, making it an [[isomer]] of sucrose.

==See also==
* [[Lac operon]]
* [[Lactic acid]]
* [[Lactose intolerance]]
* [[Nectar]]
* [[Sugars in wine]]

==References==
{{Reflist}}

==External links==
* {{Commons category-inline}}

{{Carbohydrates}}
{{Sugar}}
{{Authority control}}

[[Category:Lactose| ]]
[[Category:1633 introductions]]
[[Category:Disaccharides]]
[[Category:Excipients]]
[[Category:Types of sugar]]