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
I. Removal of proteins and fats from the milk
- 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.
- Measure the pH using a litmus paper. It shall be around 4.5.
- 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
- Take 5 ml of supernatant in a test tube.
- Make the supernatant alkaline by adding a little amount of ammonia into it.
- 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
- Follow the procedure from (i) to (iii) and take small amount of casein-free and fat- free
- Add 1 ml of concentrated nitric acid and shake well.
- 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