Review/Oorsig Volume 22, Issue 05 - Page 12

Oorsig/Review The significance of Lactose in Milk Dr Mark Chimes, BVSc* Ask any veterinarian or dairy farmer why we test Lactose levels in milk and what the test results tell us, and you will get a blank stare. It is the orphan of the milk analyses results. Although the test results do not tell us a lot, it is the most important constituent in milk that determines the volume of milk that is produced. INTRODUCTION Lactose is the major carbohydrate fraction in milk. It is a disaccharide made up of two sugar molecules, namely Glucose and Galactose. Lactose production in nature is limited to mammals where the enzyme lactose synthase binds a Glucose and Galactose molecule to form Lactose. Lactose is less sweet than other sugars (such as glucose, sucrose and fructose) and less water soluble. Cow’s milk comprises 4-5% Lactose with an average of 4.7 – 4.9% and provides up to 30% of the neonate’s energy needs. By contrast human milk comprises 7.2% Lactose, which is among the highest levels of lactose in the mammalian world and provides up to 50% of the neonate’s energy needs. Lactose is a major, readily digestible source of glucose which provides energy for the neonate. An enzyme called lactase (ß-galactosidase) splits Lactose into Glucose and Galactose in the intestine of the neonate where it is absorbed across the intestinal mucosa. The galactose is then converted to another glucose by a different enzyme and used as energy. Lactase production in most humans starts to wane in late childhood. This leads to maldigestion 12 of lactose in most cases and lactose intolerance in more severe cases. THE ROLE OF LACTOSE Lactose is the principal carbohydrate in milk and is split into two simpler sugars namely, Glucose and Galactose, by the enzyme lactase CH 2 OH OH CH 2 OH O H OH H H OH H H O OH O H OH OH H H Lactose H OH Lactase CH 2 OH H C OH C H CH 2 OH O H HO H H C C C C OH H OH OH Glucose C H O OH OH H C C C H H OH Galactose in the intestine. The sugars are then absorbed across the intestinal mucosa and used directly as the primary source of energy by the infant. Galactose plays an important role in the nervous system and brain structure development of the neonate. It is a substrate of several macromolecules (cerebrosides, gangliosides and mucoproteins), which are used in the synthesis of nerve cell membranes. Galactocerebroside is