Lactose is a disaccharide of D-galactose and D-glucose (Gal β1‑4 Glc). Lactose is the most abundant solid component and the principal carbohydrate in human milk. It is also called milk sugar. The mean concentration is approx. 70 g/l (Zivkovic et al. 2010). Lactose represents the major energy substrate of human milk and is bifidogenic (Ballard and Morrow. 2013).