Lactose . Disaccharide formed by the union of one molecule of glucose and one galactose . Specifically, a β-galactopyranose and a β-glucopyranose linked by carbons 1 and 4, respectively, intervene.


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  • 1 General
  • 2 Lactose biosynthesis
  • 3 Chemical properties of lactose
  • 4 Solubility
  • 5 Sensitivity to heat
  • 6 Fermentation
  • 7 Use of lactose
  • 8 Lactose intolerance
  • 9 Source


Lactose is a very rare sugar in nature, except in milk , of which it is the most important carbohydrate in almost all species. It has also been found in the fruits of some members of the Sapotaceae family. In milk, its concentration varies from zero in some seals to approximately 100 g / liter in that of certain primates. Milk cow contain commonly more than any other component lactose solid , with an average concentration of 50 g / liter.

Lactose biosynthesis

Lactose biosynthesis consists of coupling galactose with glucose via a β-1,4-glycosidic bond. It is synthesized in the mammary gland from glucose in the blood . This can be considered as one of the components of milk that presents less fluctuations in its content and when this occurs it indicates abnormalities in the animal’s mammary gland. Lactose synthesis largely regulates the volume of milk secreted; that is, the amount of milk produced depends on the possibilities of lactose synthesis in the breast.

Chemical properties of lactose

From a chemical point of view, lactose is a reducing [[carbohydrate] belonging to the group of [[diholosides], hydrolyzing glucose and galactose. Lactose is found in milk in two chemical isomeric forms: alpha and beta, they differ from each other by the position of the OH group, by the uneven rotation of the polarized ray and by its different solubility in water. Lactose is not as sweet as other common sugars: sucrose, glucose and fructose. At higher concentrations it is relatively sweeter. For example, 1, 5, 10, and 20% sucrose solutions have the same sweetening power as lactose solutions of 3.5%, 15%, 30%, and 33%. Β-lactose is sweeter than α-lactose, but such difference is not important, since when the anomers are balanced it is quickly eliminated.


In milklactose is in a state of true solution and it is very interesting from an industrial point of view to know its solubility. If an excess of commercial lactose (alpha form) is dissolved in water at a certain temperature, a certain amount is observed to dissolve rapidly and therefore represents initial solubility. If this solution is stirred for 24 h, it will be observed that a new amount of lactose dissolves and then the final solubility can be determined. In that time a portion of lactose alpha has been transformed into more soluble beta lactose, which has allowed a new amount of lactose alpha to enter solution. In other words, there is a constant balance in the liquid between both forms of lactose, this balance follows defined and variable proportions with temperature. When the solution is saturated with beta lactose, then the final solubility is reached. C) this saturation takes place when the beta lactose content reaches 62% and therefore 38% is lactose alpha.°At a temperature of 288K (15  The phenomenon of lactose solubility can be followed by studying the polarimetric deviation or rotation. This phenomenon is known by the name of mutarotation.

Heat sensitivity

Lactose is heat sensitive from 383 to 403 K (110 to 130 ° C) in a hydrated form it loses its crystallization water. After 423 K (15 ° C) it turns yellow and after 423 K (17 ° C) a pronounced darkening occurs due to caramelization. In contrast, in milk it is observed that darkening occurs at much lower temperatures. This phenomenon is not caused by the caramelization of lactose, but by a reaction of lactose with nitrogenous materials, forming dark reducing compounds called melanoidins. This very complex reaction catalyzed by iron , copper, and phosphates is known as the Maillard reaction.


Lactose is the weakest component of milk compared to microbial action. Milk is easily preyed upon by bacteria of various kinds, which transform lactose into lactic acid and other aliphatic acids; sometimes harmful and often very useful transformation. The microorganisms transform lactose into lactic acid, thus causing lactic fermentation, which results in milk coagulation. Lactose can also undergo alcoholic fermentation when it is attacked by yeasts that produce an enzyme that hydrolyzes this sugar into glucose and galactose.

Use of lactose

Lactose represents an energy source that is easy to use and favors the absorption of calcium and magnesium . The bacteria of lactic acid include, among others, species of the genera Streptococcus and Lactobacillus which produce yogurt.

Lactose intolerance

In humans, the presence of the enzyme lactase is necessary for the correct absorption of lactose. When the body is not capable of assimilating lactose correctly, various discomforts appear whose origin is called lactose intolerance .


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