Dairy MicrobiologyMicrobiology

Detection Of Calcium And Phosphorus In Milk

Calcium and phosphorus are the important components of the milk. A growing baby derives Ca and P from the milk nourishing mothers/animals. Here, presence of these two in milk can be tested chemically. The first approach is to make milk free from protein and fat because unless these are separated, Ca and P cannot be tested.


  • Small amount of milk
  • Boiling test tubes
  • Test tubes
  • Spirit lamp
  • Filter paper
  • Buchner funnel
  • Acetic acid
  • Nitric acid
  • Ammonium oxalate
  • Litmus paper
  • Beakers


 I. Removal of proteins and fats from the milk

  1. Take small amount (10 ml) of milk in a boiling test tube and add 1% acetic acid until a white precipitate appears in the milk.
  2. Measure the pH using a litmus paper. It shall be around 4.5.
  3. Put a filter paper in a funnel, filter the acidified milk and collect the supernatant. The supernatant contains Ca and P.

II. Detection of Ca in milk supernatant

  1. Take 5 ml of supernatant in a test tube.
  2. Make the supernatant alkaline by adding a little amount of ammonia into it.
  3. Now, add ammonium oxalate into the supernatant.


A white precipitate appears on the top layer of the supernatant due to formation of calcium

oxalate. It shows the presence of Ca in milk.

III. Detection of P in milk supernatant

  1. Follow the procedure from (i) to (iii) and take small amount of casein-free and fat- free
  2. supernatant.
  3. Add 1 ml of concentrated nitric acid and shake well.
  4. Add 3 ml of ammonium molybdate.


Yellow colour or yellow precipitate appears in the supernatant. This colour change is due to the presence of phosphorus in the milk.


Dr. R. C. Dubey – Practical Microbiology

Gaurav Singh

Editor in Chief Medical Microbiology & Recombinant DNA Technology (RDT) Labs - RDT Labs Magazine

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