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2. Milk -
Fluid secreted by mammals for nourishment
of young
White or yellow-white, opaque liquid
Colostrum –
Concentrated fluid secreted immediately
after parturition

3. Physical Properties of Milk
• Colour and optical properties
• Flavor of milk
• Specific gravity and density
• Viscosity
• Surface tension
• Freezing point and boiling point of milk
• Acidity and pH
• Heat stability of milk

4. Physical Properties of Milk
Colour and optical properties
• Turbid and opaque - light scattering by fat
globules and protein micelle
• Skim milk - slight blue - higher protein
content
• Creamy colour of cow milk - Beta-carotene
content
• Greenish tinge in whey - Riboflavin
• Refractive index - ranges from 1.3440 to 1.3485
at 20ºC.
Flavour of milk
• Naturally - sweet flavor
• Off-flavours develop quickly in milk –feed,
bacterial growth, enzyme activities, oxidative
reactions, etc.
• Bacterial growth - fruity, barny, malty or acid

5. Chemical Properties of Milk - Composition of
Milk
Several factors influence
• Age and health of the animal
• Breed of animal
• Seasonal changes
• Weather
• Nature and quality of feed
• Stage of lactation, etc.
Major components - water, fat, protein and
lactose minerals, vitamins and enzymes
Fresh milk from a healthy cow - free from
bacteria

6. Water
The principal constituent in milk - 79% to 90%
All other constituents - dissolved or suspended in water
Water activity in milk is high - 0.993
Removal of water increases shelf life of milk
Powdered milk have more shelf life

7. Lipid content
• Most variable feature
• Main fatty acids
• C14 (myristic)
• C16 (palmitic)
• C18 (stearic
• C18:1 (oleic)
• Present in fresh milk as fat globules
• Surrounded by phospholipid layer (milk
fat globule membrane)
• Diameter about 5 mm
• Milk contains about 1012 fat globules
per litre
• Upon standing, the fat rises to the
surface of the milk and produce cream line
• Homogenization reduces this tendency

8. Minerals - All essential for human nutrition
• Potassium, Sodium, Calcium, Magnesium,
Chloride, phosphate esters
Enzymes - 20 different enzymes
• Lipoprotein lipase
• Alkaline phosphatase
• Sulfhydryl oxidase
• Lactoperoxidase
• Catalase
• Xanthine oxidase
• Superoxide dismutase
• γ- Glutamyltransferase, etc.