2.2.3. Lactose

Lactose (milk sugar) is a ready source of energy, participates in the formation of the nervous system, skin, bone, and cartilage tissue in childhood and prevent bone loss in the elderly [26].

The lactose content in milk of cows is 3.6–5.6 (4.7% on average). Lactose is a disaccharide built from d-glucose and d-galactose residues linked by a 1.4-glycosidic bond. Lactose is 5–6 times less sweet than sucrose and less soluble in water. In milk, milk sugar is in two forms: α and β. At 20 ◦C contains 40% α-lactose and 60% β-lactose. Both forms can transform one into another, the rate of transition from one form to another depends on the temperature. When milk is heated to a temperature above 100 ◦C (especially during sterilization and high-temperature processing), milk sugar is partially converted into lactulose. Lactulose differs from milk sugar in that it contains fructose instead of glucose. Lactulose is readily soluble in water, 1.5–2 times sweeter than lactose. At high heating temperatures (160–180 ◦C), milk sugar caramelizes, and the lactose solution turns brown.
