LPT 311: Milk and Milk Products Technology (1+1)

Milk Carbohydrate (Lactose)

MILK CARBOHYDRATE

Carbohydrates are sugar substances made up of molecules called saccharides.

• Lactose: Lactose is the milk carbohydrate which is a disaccharide comprising of glucose and galactose. Milk contains approximately 4.9% carbohydrate that is predominately lactose with trace amounts of monosaccharides and oligosaccharides.
• Physical Properties of Lactose
• Lactose exist in solution portion/ serum phase in a dissolved form of fluid milk. Two isomeric forms of lactose, called the α-lactose hydrate anomer and ß-lactose hydrate anomer are found in milk. They get converted back and forth between each other.
• Crystallization of lactose occurs when the concentration of lactose exceeds its solubility. The physical properties of lactose crystals are dependent on the crystal type and can greatly influence thei texture of final product. Temperature affects the equilibrium ratio of the α- and ß-lactose anomers. Lactose crystals formed at temperatures below 70°F (20°C) are mainly α-lactose crystals. The α-monohydrate lactose crystals are very hard and form, as in ice cream which goes through numerous warming and freezing cycles. This results in an undesirable gritty, sandy texture in the ice cream and condensed milk. The crystal form of ß-lactose is sweeter and more soluble than the α-monohydrate lactose and may be preferred in some bakery applications. When a lactose solution is rapidly dried it does not have time to crystallize and forms a type of glass. Lactose glass exists in milk powders and causes clumping due to highly hygroscopic nature.
• Influence of heat treatments on lactose properties
• Lactose is not influenced much by the normal pasteurization conditions. High temperatures used for ultra high temperature (UHT) pasteurization of extended shelf life products and spray drying can cause browning and isomerization reactions, which may affect product quality and nutritional properties. Maillard reaction (The browning reaction), occurs between the lactose and free amino group of protein in milk and produces undesirable flavors and color, and decreases the available content of the amino acid lysine in milk protein. The isomerization reaction is a molecular rearrangement of lactose to lactulose. Lactulose is produced by alcoholic isomerisation of lactose and is used by the pharmaceutical industry in pill production.