Physical and Chemical Properties of Milk

Physical and Chemical Properties of Milk
Physical Properties

1.      Colour:

·         Milk is an Opaque fluid varies from White, Yellow White. White colour is due to Reflection of light by Casein protein and Calcium salt in Milk.

·         Buffalo, Sheep, Goat have White milk colour.

·         Cow has Yellow due to Carotene.

·         Diet also Affect colour.

·         Yellow Milk in grass feed cow due to Carotein and White Yellowish colour in Stall feed cow.

·         Bluish White milk in case of Skim Milk due to Casein

·         Greenish Colour appear due to Riboflavin.

2.      Taste and Flavour:

·         Milk is Sweeter in Taste. This is due to Lactose.

·         Chlorides which are Salty to bitter also Control apart of milk taste. So more lactose make milk sweeter.

Chloride Lactose Number = % of Chloride / % of lactose × 100.

·         If Value is 1.2-2 than milk is good quality and good taste.

·         The flavour of milk is based on chloride lactose numbr.

3.      Specific Gravity:

·         Specific gravity of water is 1.

·         Buffalo and Sheep is 1.028.

·         Goat has 1.02.

·         Cow has 1.032.

·         Camel has 1.014-1.017.  

·         Human has 1.027-1.034.  

·         Lactometer is use to determine S.G.

4.      Density:

·         Density of Milk is 1028-1035 kg/m3

·         Hydrometer is used to determine density at 20 C.

·         It is used in conjunction with fat test to estimate the content of total solid.

5.      Refrective Index:

·         Adulteration is check by this.

·         It is used sometime to indicate the adulteration of Milk specially water.

6.      Freezing Point:

·         Milk freezes at 0.535-0.55 C.

·         Milk freezes at temp slightly lower than water due to soluble constituent.

7.      Boiling:

·         100.17-101 C.

8.      Viscosity:

It Depend upon

·         Temperature

·         Composition

·         Physical state of disperse substance including milk fat.

·         Viscosity of milk varies from 1.5-2 centipoises.

Chemical Properties;

1)      pH of milk.

·         pH 6.5-6.7 due to certain phosphate lactic acid bacteria present in it start growing at room temp.

·         The acid nature of freshly drawn milk is due to presence of phosphate, citrate, and casein and dissolves CO2.

·         In cow due to Mastitis pH is increase.

·         In clostrum pH is low.

·         High pH of milk Indicate that animal suffering from udder infection.

·         Low pH of milk that less than 6.5 is considered to be due to added Clostrum or Bacterial Deterioration.

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