The Role and Properties of Lactose in Milk and Dairy Products

Lactose, commonly referred to as milk sugar, is the primary carbohydrate found in milk. As a disaccharide, lactose consists of two monosaccharides: glucose and galactose. This milk sugar is found in a true solution within milk, making it easily accessible for various biochemical processes. Besides lactose, milk also contains trace amounts of other sugars like glucose, galactose, and oligosaccharides.

Lactose plays a crucial role in dairy products due to its ability to be fermented by lactic acid bacteria, which convert it into lactic acid. This fermentation process is essential for the production of yogurt, cheese, and other fermented dairy products, as it influences texture, flavor, and preservation.

Lactose exists in two isomeric forms: α-lactose and β-lactose. The β-lactose form is more soluble in water than the α-lactose form, affecting the solubility and crystallization of lactose in dairy products. In cow's milk, lactose makes up approximately 4.9% of the milk's composition. Interestingly, the lactose content of milk is inversely related to its ash content, meaning higher ash content correlates with lower lactose levels.

Furthermore, udder infections can significantly impact milk composition. Such infections often lead to increased chloride levels in milk and a reduction in lactose secretion, highlighting the sensitivity of lactose production to the cow's health. Understanding these dynamics is crucial for dairy production and quality control.
The Role and Properties of Lactose in Milk and Dairy Products

Milk lactose – main roles in human body

Milk is an emulsion produced by mammary glands which characterise with white colour, mild taste and flavour.

The major constituent of milk is water, but milk contains varying levels of lipids, proteins, and carbohydrates which are synthesized within with mammal gland. Their composition is influenced by animal species, environmental conditions, nutrition of animals, their lactation state and others.

Lactose is the principal carbohydrate found in milk. It is virtually unique to milk, having been found elsewhere only in fruits of certain members of the Sapotaceae. Lactose is consumed through milk and other unfermented dairy products, such as ice cream.

Disaccharides lactose in milk imparts sweet profile and human milk has a major concentration of lactose (7.4%) compared to milk of other species. The main role of lactose includes:
*It provides galactose for the synthesis of the nerve structures of the growing infant
*In the intestine, it gets metabolized to lactic acid which eliminates harmful bacteria.

Lactase is a membrane-bound enzyme located in the brush border epithelial cells of the small intestine. Once lactose reaching the small intestine, where the hydrolytic enzyme lactase (β-galactosidase) is located, lactase catalyzes the hydrolysis of lactose into its constituent monosaccharides (glucose and galactose). Only monosaccharides among the carbohydrates are absorbed from the intestines.

Lactose accounts for ~30% of the caloric value of whole milk. Lactose is an important energy source and sometimes it is referred to simply as milk sugar, as it is present in high percentages in milk. Lactose-intolerance individuals have a lactase deficiency; therefore, lactose is not completely catabolized.
Milk lactose – main roles in human body