from Wikipedia, the free encyclopedia
Structural formula
Structural formula of lactose
Surname Lactose
other names
  • lactose
  • Lactose
  • α-lactose monohydrate, gen. Commercial form
  • Lactobiosis
  • Saccharum lactis
  • D -Galactopyranosyl-β- (1 → 4) - D -glucopyranose
  • 4- O - (β- D -galactopyranosyl) - D -glucopyranose ( IUPAC )
Molecular formula C 12 H 22 O 11
Brief description

colorless, crystalline solid

External identifiers / databases
CAS number 63-42-3


EC number 200-559-2
ECHA InfoCard 100,000,509
PubChem 6134
Wikidata Q127900
Molar mass 342.29 g mol −1
Physical state



1.525 g cm −3

Melting point

202 ° C

  • soluble in water
    • GGW mixture: 21.6 g 100 g −1 (25 ° C)
    • α-form: 5.0 g 100 g −1 (0 ° C)
    • β-form: 45.1 g 100 g −1 (0 ° C)
safety instructions
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Lactose monohydrate, crystal, reflected light, polarization, microscopic

Lactose , milk sugar or lactose (from Latin lac , genitive lactis milk) is a sugar contained in milk . The disaccharide consists of the two molecules D - galactose and D - glucose , which are connected to one another via a β-1,4- glycosidic bond . According to IUPAC , lactose is referred to as 4- O - (β- D- galactopyranosyl) - D -glucopyranose ; it was first isolated from milk around 1615 by Fabrizio Bartoletti . It occurs as the main source of energy in the milk of mammals . Lactose is digested in the small intestine by the enzyme lactase ; H. split into glucose and galactose. Lactase deficiency can lead to lactose intolerance in adults . The transport and breakdown of lactose in bacteria is controlled by the lac operon .

Occurrence and extraction

In mammalian milk as well as in milk products , lactose makes up almost all of the carbohydrates. The amount of lactose in dairy products varies due to the manufacturing process. During cheese production, part of the lactose is separated off with the whey and further broken down through maturation. Fresh cheeses therefore have a lactose content of more than 2% and longer-matured hard cheeses often less than 0.1% lactose.

Cow's milk contains up to 47 g / l lactose. It is obtained from sweet or sour whey , which is obtained in large quantities as a by-product in cheese production. For this purpose, the whey is freed from lipids, proteins and minerals by heating, ultrafiltration and ion exchange and concentrated in a vacuum. The lactose then crystallizes from the concentrated solution.

mammal Share of
ass 7.4%
human 7.1%
horse 6.2%
camel 5.0%
buffalo 4.8%
cat 4.8%
sheep 4.8%
cow 4.6%
yak 4.6%
goat 4.3%
reindeer 2.8%
Dairy products (cow) Share of lactose in g / 100 g
Whole milk 4.70 g
Skimmed milk (0.3% fat) 4.80 g
low-fat milk (1.5-1.8% fat) 4.80 g
Dry milk (whole milk powder) 35.10 g
Skimmed milk powder 50.50 g
Condensed milk 9.32 g
Whipped cream 3.27 g
sour cream 3.0 g
whey 4.70 g
Yogurt (3.5% fat) 3.19 g
Milk chocolate 2.0 g


β- D -lactose in the chair shape

Lactose is a crystalline, colorless substance with a sweet taste; the sweetening power is between 25 and 60% that of sucrose, depending on the concentration . In its anhydrous form, lactose is hygroscopic ; crystallized from the aqueous solution, the more stable α-form as a mono hydrate from. Milk sugar is less water soluble than other sugars such as maltose . The water solubility of the α and β forms differs considerably (5 and 45 g / 100 g at 0 ° C). Milk sugar is optically active and is one of the reducing sugars .

The individual components of lactose, galactose and glucose , are linked to one another via a β-1,4- glycosidic bond . In aqueous solution there is an equilibrium between α- and β- D -form of the glucose part due to mutarotation , sometimes also in open-chain form. Due to the presence of residual glucose, lactose as a reducing sugar gives a positive Tollens or Fehling test . The Wöhlk reaction with alkaline ammonia solution makes it possible to differentiate between lactose (salmon-red color), glucose (yellow color) and sucrose (colorless). In the variant according to Fearon , using primary alkylamines instead of ammonia, an accelerated detection in the inverter microwave oven succeeds.

When heated or in an alkaline solution, lactose is partially rearranged into lactulose , which tastes sweeter than milk sugar.


The reliable qualitative and quantitative determination of lactose in different test material such as B. cheese, milk , vegetable material or drugs can be achieved after appropriate sample preparation by coupling gas chromatography or HPLC with mass spectrometry .

Physiological importance

UDP galactose

As an ingredient in breast milk, lactose is the main source of energy for infants . It arises in the mammary gland through the enzymatic transfer of glucose to uridine diphosphate galactose (UDP-galactose) with splitting of the UDP. In order to be able to utilize lactose, it has to be broken down into the simple sugars D- galactose and D- glucose during digestion . This requires the enzyme lactase , which is present in the small intestine and is only formed in smaller quantities in adulthood. If lactose cannot be digested due to a lack of lactase and therefore cannot be absorbed through the intestinal wall, this results in lactose intolerance or intolerance.



Web links

Commons : Lactose  - Collection of pictures, videos and audio files
Wiktionary: Lactose  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. a b c d Entry on lactose in the GESTIS substance database of the IFA , accessed on April 26, 2012(JavaScript required) .
  2. a b c d e f H.-D. Belitz , W. Grosch, Peter Schieberle : Textbook of food chemistry. 6th edition. Springer 2007, ISBN 978-3-540-73201-3 , p. 530.
  3. Wilhelm Fleischmann : History of milk and milk sugar. In: Sudhoff's archive. 4, 1911, pp. 1-19, JSTOR 20772893 .
  4. a b H.-D. Belitz, W. Grosch, P. Schieberle: Textbook of food chemistry. 6th edition. Springer 2007, ISBN 978-3-540-73201-3 , p. 517.
  5. Entry on milk. In: Römpp Online . Georg Thieme Verlag, accessed on January 28, 2014.
  6. Entry on lactose. In: Römpp Online . Georg Thieme Verlag, accessed on January 28, 2014.
  7. German Research Institute for Food Chemistry, Garching (ed.): Food table for practice . The little souci · specialist · herb. 4th edition. Wissenschaftliche Verlagsgesellschaft, Stuttgart 2009, ISBN 978-3-8047-2541-6 , p. 20-21 .
  8. Klaus Ruppersberg, Julia Hain: How can the lactose content of dairy products be made visible in school experiments? Rediscovering the Wöhlk reaction for chemistry class . In: Chemistry in concrete terms - ChemKon . tape 23 , no. 2 , 2016 ( [accessed on March 14, 2018]).
  9. Klaus Ruppersberg, Horst Klemeyer: How to detect lactose in 60 seconds by using an inverter microwave oven! Quick test: how can you detect lactose in 60 seconds? 2019 ( [accessed April 20, 2020]).
  10. H. Ochi, Y. Sakai, H. Koishihara, F. Abe, T. Bamba, E. Fukusaki: Monitoring the ripening process of Cheddar cheese based on hydrophilic component profiling using gas chromatography-mass spectrometry. In: J Dairy Sci. 96 (12), 2013, pp. 7427-7441. PMID 24140316
  11. G. Fusch, A. Choi, N. Rochow, C. Fusch: Quantification of lactose content in human and cow's milk using UPLC-tandem mass spectrometry. In: J Chromatogr B Analyt Technol Biomed Life Sci. 879 (31), Dec 1, 2011, pp. 3759-3762. PMID 22041090
  12. S. Gabbanini, E. Lucchi, F. Guidugli, R. Matera, L. Valgimigli: Anomeric discrimination and rapid analysis of underivatized lactose, maltose, and sucrose in vegetable matrices by U-HPLC-ESI-MS / MS using porous graphitic carbon. In: J Mass Spectrom. 45 (9), Sep 2010, pp. 1012-1018. PMID 20862732
  13. F. Monajjemzadeh, D. Hassanzadeh, H. Valizadeh, MR Siahi-Shadbad, JS Mojarrad, TA Robertson, MS Roberts: Compatibility studies of acyclovir and lactose in physical mixtures and commercial tablets. In: Eur J Pharm Biopharm. 73 (3), Nov 2009, pp. 404-413. PMID 19631740
  14. Fritz Höffeler: History and evolution of lactose (in) tolerance. The legacy of the early ranchers . In: Wiley (Ed.): Biology in our time . December 11, 2009, doi : 10.1002 / biuz.200910405 .