View source for Maltose

{{Use dmy dates|date=March 2018}}
{{chembox
| Verifiedfields = changed
| Watchedfields  = removed
| verifiedrevid  = 47716923
| ImageFile      = Maltose2.svg
| ImageSize      = 
| ImageName      = α-Maltose
| ImageCaption   = α-Maltose
| ImageClass     = skin-invert-image
| ImageFile1     = Maltose structure.svg
| ImageSize1     = 
| ImageName1     = β-Maltose
| ImageCaption1  = β-Maltose
| ImageClass1    = skin-invert-image
| IUPACName      = α-{{sm|d}}-Glucopyranosyl-(1→4)-β-{{sm|d}}-glucopyranose<br>
4-''O''-α-<small>D</small>-Glucopyranosyl-<small>D</small>-glucopyranose
| OtherNames     = 
| SystematicName = (3''R'',4''R'',5''S'',6''R'')-6-(hydroxymethyl)-5-{{(}}[(2''R'',3''R'',4''S'',5''S'',6''R'')-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxy}oxane-2,3,4-triol
| Section1       = {{Chembox Identifiers
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 17306
| SMILES = O([C@H]1[C@H](O)[C@@H](O)C(O)O[C@@H]1CO)[C@H]2O[C@@H]([C@@H](O)[C@H](O)[C@H]2O)CO
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 66Y63L379N
| KEGG = D00044
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 1234209
| 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-PICCSMPSSA-N
| ChemSpiderID1_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID1 = 6019
| ChemSpiderID1_Comment = β-maltose
| 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
| InChIKey1 = GUBGYTABKSRVRQ-PICCSMPSSA-N
| CASNo = 69-79-4
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNoOther =
| EC_number = 200-716-5
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 388469
| ChemSpiderID_Comment = α-maltose
| PubChem = 6255
  }}
| Section2       = {{Chembox Properties
| Properties_ref = <ref>{{RubberBible62nd|page=C-367}}.</ref>
| C=12 | H=22 | O=11
| Appearance = White powder or crystals
| Density = 1.54 g/cm<sup>3</sup>
| MeltingPtC = 160 to 165
| MeltingPt_notes = (anhydrous)<br />102–103&nbsp;°C (monohydrate)
| Solubility = 1.080 g/mL (20&nbsp;°C)
| SpecRotation = +140.7° (H<sub>2</sub>O, ''c'' = 10)
  }}
| Section7       = {{Chembox Hazards
| ExternalSDS = [https://www.merckmillipore.com/INTERSHOP/web/WFS/Merck-GB-Site/en_US/-/GBP/ProcessMSDS-Start?PlainSKU=MDA_CHEM-105912&ReferrerURL=https%3A%2F%2Fwww.google.co.uk%2F&Origin=SERP&bd=1 External MSDS]
| AutoignitionPt =
  }}
| Section8       = {{Chembox Related
| OtherFunction = [[Sucrose]]<br />[[Lactose]]<br />[[Trehalose]]<br />[[Cellobiose]]
  }}
}}
[[Image:Amylase reaction.png|thumb|right|260px|Amylase reaction consisting of hydrolyzing amylose, producing maltose]]

'''Maltose''' ({{IPAc-en|ˈ|m|ɔː|l|t|oʊ|s}}<ref>Dictionary Reference: [http://dictionary.reference.com/browse/maltose maltose]</ref> or {{IPAc-en|ˈ|m|ɔː|l|t|oʊ|z}}<ref>Cambridge dictionary: [http://dictionary.cambridge.org/dictionary/british/maltose maltose]</ref>), also known as '''maltobiose''' or '''malt sugar''', is a [[disaccharide]] formed from two units of [[glucose]] joined with an α(1→4) [[glycosidic bond|bond]]. In the [[isomer]] [[isomaltose]], the two glucose molecules are joined with an α(1→6) bond. Maltose is the two-unit member of the [[amylose]] [[homologous series]], the key structural motif of [[starch]]. When [[beta-amylase]] breaks down starch, it removes two glucose units at a time, producing maltose. An example of this reaction is found in [[germination|germinating]] seeds, which is why it was named after [[malt]].<ref name=Stoker>{{Cite book|url=https://books.google.com/books?id=HRCdBQAAQBAJ&pg=PA278|title=Organic and Biological Chemistry|last=Stoker|first=H. Stephen|date=2015-01-02|publisher=Cengage Learning|isbn=9781305686458|language=en}}</ref> Unlike [[sucrose]], it is a [[reducing sugar]].<ref name="Fruton">{{cite book|last1=Fruton|first1=Joseph S|title=Proteins, Enzymes, Genes: The Interplay of Chemistry and Biology|date=1999|publisher=Yale University Press|location=Chelsea, Michigan|isbn=0300153597|page=144|url=https://books.google.com/books?id=X6skaZlZNdsC&pg=PA144|access-date=21 October 2017|language=en}}</ref>

== History ==
Maltose was discovered by [[Augustin-Pierre Dubrunfaut]], although this discovery was not widely accepted until it was confirmed in 1872 by Irish chemist and brewer [[Cornelius O'Sullivan]].<ref name="Fruton" /><ref>{{cite journal|last1=O'Sullivan|first1=Cornelius|title=XXI.?On the transformation-products of starch|journal=Journal of the Chemical Society|date=1872|volume=25|pages=579–588|doi=10.1039/JS8722500579|url=https://pubs.rsc.org/en/Content/ArticleLanding/1872/JS/js8722500579|access-date=11 December 2014}}</ref> Its name comes from [[malt]], combined with the suffix '[[-ose]]' which is used in names of sugars.<ref name=Stoker />

== Structure and nomenclature ==
Carbohydrates are generally divided into [[monosaccharide]]s, [[oligosaccharide]]s, and [[polysaccharide]]s depending on the number of sugar subunits. Maltose, with two sugar units, is a disaccharide, which falls under oligosaccharides. Glucose is a [[hexose]]: a monosaccharide containing six carbon atoms. The two glucose units are in the [[pyranose]] form and are joined by an [[glycosidic bond|O-glycosidic bond]], with the first carbon (C<sub>1</sub>) of the first [[glucose]] linked to the fourth carbon (C<sub>4</sub>) of the second [[glucose]], indicated as (1→4). The link is characterized as α because the glycosidic bond to the anomeric carbon (C<sub>1</sub>) is in the opposite plane from the {{chem|C|H|2|O|H}} [[substituent]] in the same ring (C<sub>6</sub> of the first glucose). If the glycosidic bond to the anomeric carbon (C<sub>1</sub>) were in the same plane as the {{chem|C|H|2|O|H}} substituent, it would be classified as a '''β(1→4)''' bond, and the resulting molecule would be [[cellobiose]]. The anomeric carbon (C<sub>1</sub>) of the second glucose molecule, which is not involved in a glycosidic bond, could be either an α- or β-anomer depending on the bond direction of the attached hydroxyl group relative to the {{chem|C|H|2|O|H}} substituent of the same ring, resulting in either α-maltose or β-maltose.{{Citation needed|date=January 2021}}

An [[isomer]] of maltose is [[isomaltose]]. This is similar to maltose but instead of a bond in the α(1→4) position, it is in the α(1→6) position, the same bond that is found at the branch points of [[glycogen]] and [[amylopectin]].{{Citation needed|date=January 2021}}

== Properties ==
Like glucose, maltose is a [[reducing sugar]], because the ring of one of the two glucose units can open to present a free [[aldehyde]] group; the other one cannot because of the nature of the glycosidic bond. Maltose can be broken down to glucose by the [[maltase]] enzyme, which catalyses the hydrolysis of the glycosidic bond.{{Citation needed|date=January 2021}}

Maltose in aqueous solution exhibits [[mutarotation]], because the α and β isomers that are formed by the different conformations of the anomeric carbon have different [[specific rotation]]s, and in aqueous solutions, these two forms are in equilibrium. Maltose can easily be detected by the Woehlk test or Fearon's test on methylamine.<ref>{{Cite journal|url=http://www.chemistryviews.org/details/education/10821368/150_Years_Alfred_wohlk.html|title=150 Years Alfred Wöhlk :: Education|website=ChemistryViews|date=6 March 2018 |doi=10.1002/chemv.201800002|author-first1=Klaus|author-last1=Ruppersberg|author-first2=Janet|author-last2=Blankenburg|url-access=subscription}}</ref>

It has a sweet taste, but is only about 30–60% as sweet as sugar, depending on the concentration.<ref>{{Cite book|url=https://books.google.com/books?id=xteiARU46SQC&pg=PA863|title=Food Chemistry|last1=Belitz|first1=H.-D.|last2=Grosch|first2=Werner|last3=Schieberle|first3=Peter|date=2009-01-15|publisher=Springer Science & Business Media|isbn=9783540699330|pages=863|language=en}}</ref> A 10% solution of maltose is 35% as sweet as sucrose.<ref>{{Cite book|url=https://books.google.com/books?id=db5QAwAAQBAJ&pg=PA271|title=Optimising Sweet Taste in Foods|last=Spillane|first=W. J.|date=2006-07-17|publisher=Woodhead Publishing|isbn=9781845691646|pages=271|language=en}}</ref>

== Sources and absorption ==
[[Image:Maltose syrup.jpg|thumb|right|Maltose syrup]]
Maltose is a [[malt]] component, a substance obtained when the grain is softened in water and germinates. It is also present in highly variable quantities in partially hydrolyzed starch products like [[maltodextrin]], [[corn syrup]] and acid-thinned starch.<ref>{{Cite book|url=https://books.google.com/books?id=XcSp015g4X0C&pg=PA45|title=CRC Handbook of Food Additives, Second Edition|last=Furia|first=Thomas E.|date=1973-01-02|publisher=CRC Press|isbn=9780849305429|language=en}}</ref>

Outside of plants, maltose is also (likely) found in [[sugarbag|honey]].<ref>{{Cite book |last=Heard |first=Tim |date=2015-10-30 |title=The Australian Native Bee Book|publisher=Sugarbag Bees|isbn=9780646939971|language=en}}</ref>

In humans, maltose is broken down by various maltase enzymes, providing two glucose molecules that can be [[Glucose metabolism|further processed]]: either broken down to provide energy, or stored as glycogen. The lack of the [[sucrase-isomaltase]] enzyme in humans causes [[sucrose intolerance]], but complete maltose intolerance is extremely rare because there are four different maltase enzymes.<ref>{{Cite book|url=https://books.google.com/books?id=whILjP8XUS4C&pg=PA60|title=Control of Glycogen Metabolism|last1=Whelan|first1=W. J.|last2=Cameron|first2=Margaret P.|date=2009-09-16|publisher=John Wiley & Sons|isbn=9780470716885|pages=60|language=en}}</ref>

== References ==
{{Reflist}}

==External links==
*{{Commons category-inline}}
*[https://web.archive.org/web/20051124215824/http://www.elmhurst.edu/~chm/vchembook/546maltose.html Maltose], Elmhurst College Virtual Chembook.

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

[[Category:Disaccharides]]
[[Category:Starch]]
[[Category:Types of sugar]]
[[Category:Malt]]