Explain the Theory or Principle of Determination of the Quality of Milk

Milk is an ideal medium for the survival and growth of microorganisms. It contain all the nutrients, i.e., carbohydrates, proteins, vitamins, minerals and fat and has a pH of 6.8. The number and kinds of microorganism in milk depends on the milking conditions and the ways it is transported, processed and handled.

Heating and pasteurization reduces the microbial load. Milk, if not handled and processed properly, is a carrier of number of diseases like diphtheria, dysentery, Q fever, tuberculosis, typhoid etc. Quality check of the milk is needed to prevent these diseases. Commonly used methods include standard plate count, breed or direct microscopic count, coliform test and dye reduction test.