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Basic Properties of Milk
Emulsion Colloidal Solution
Emulsion: •An emulsion is a suspension of droplets of one liquid into another liquid. Milk is an emulsion of fat in water. Butter is an emulsion of water in fat. The solute is known as the dispersed phase and the solvent is known as the continuous phase. Other examples of emulsions include margarine, mayonaise, cream, and salad dressing.
Colloidal solution: •A colloidal solution is when matter exists in a state of division in between a true solution, which is sugar in water, and a suspension, which is chalk in water. The characteristics of a colloid are small particle size, electrical charge, and affinity of the particles for water molecules. •In milk, the whey proteins are in colloidal solution. The casein proteins are in colloidal suspension.
Changes in Milk Composition
Changes in composition Breed Diet Season Stage of lactation
Changes in composition The composition of milk may change due to differences in relative rates of synthesis and secretion of milk components by the mammary gland. Variations are due to differences among species, between individuals within a strain, and between conditions affecting an individual. Conditions affecting the cows may include the weather or seasons and the stage of lactation.
Breed: The US mostly uses milk from cows of the larger breeds, such as Holsteins and Brown Swiss’ because of the lower fat content and greater milk production. Breeds such as the Guernseys and the Jerseys have higher fat contents in their milks. Both the Guernseys and the Jerseys have a fat content of 5.2%, where as the Holsteins and the Brown Swiss’ have fat contents of 3.5%.
Diet: The composition of the cows’ diet and the form in which they are fed affect the composition of milk and especially milk fat. High fat and/or low roughage diets can reduce the fat content of milk. Diet has small effects on protein content and none on lactose content.
The seasonal effect is due to the changes in the diet throughout the year.
Stage of lactation •When mammals give birth, their first secreted milk is called colostrum, and it differs greatly in composition from regular milk. Colostrum contains more mineral salts and protein and less lactose than normal milk. Also, fat content, calcium, sodium, magnesium, phosphorus, and chloride are higher in colostrum than in normal milk. Whey content is about 11% in colostrum as opposed to 0.65% in normal milk. •Colostrum contains an extremely high imunoglobulin (Ig) content. Igs accumulate in the mammary gland before parturition and transfer immunity to the baby cow. These immunoglobulins protect the baby cow until it can establish its own Immunity.
•Figure 5.1 in your assigned reading