|Molecular formula||C 12 H 22 O 11|
colorless, crystalline solid
|External identifiers / databases|
|Molar mass||342.29 g mol −1|
1.525 g cm −3
202 ° C
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
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.
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.
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 .
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.
- provides energy
- supports the calcium - absorption
- inhibits putrefactive bacteria in the human intestine
- favors bifidus bacteria ( Bifidobacterium )
- Lactose is the starting material for the production of lactic acid .
- It is used to change the texture of frozen food .
- A glucose / galactose syrup is obtained by hydrolysis .
- As an additive in many products, it has a creamy consistency.
- Lactose has a laxative effect in larger quantities as it increases the osmotic pressure in the intestinal lumen .
- Due to the very low price, the high availability and almost non-existent harmfulness, it is used in galenics for the production of drugs .
- Because of its similar appearance, it is often used as an extender for common intoxicating drugs such as cocaine , amphetamine or heroin .
- H.-D. Belitz , W. Grosch, Peter Schieberle : Textbook of food chemistry. 6th edition. Springer 2007, ISBN 978-3-540-73201-3 , p. 530.
- Wilhelm Fleischmann : History of milk and milk sugar. In: Sudhoff's archive. 4, 1911, pp. 1-19, JSTOR 20772893 .
- H.-D. Belitz, W. Grosch, P. Schieberle: Textbook of food chemistry. 6th edition. Springer 2007, ISBN 978-3-540-73201-3 , p. 517.
- Entry on milk. In: Römpp Online . Georg Thieme Verlag, accessed on January 28, 2014.
- Entry on lactose. In: Römpp Online . Georg Thieme Verlag, accessed on January 28, 2014.
- 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 .
- 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 ( pedocs.de [accessed on March 14, 2018]).
- 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 ( researchgate.net [accessed April 20, 2020]).
- 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
- 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
- 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
- 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
- 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 .