Q. Determine the fat content in the given sample of milk?

After undertaking this activity, you will be able to:

• explain the technique of determination of the total fat content in the samples of milk and milk products, and

• differentiate between the different types of milk available varying in their fat percentages.

Materials Required

Samples of milk (toned/double toned and full cream milk)

The rose gottlieb tube/ separating funnels

Tared beakers

Ammonia

Diethyl ether

Petroleum ether (40-60ºC)

95% alcohol

Air-oven maintained at 100ºC

Principle

The principle of the fat extraction has been discussed in sub-section 3.3.5 earlier in this practical. Recapitulate what you learnt and write down the principle here in the space provided.

Procedure

Now carry out the experiment step-by-step as enumerated herewith:

1) Take 10 ml of the milk sample in the rose-gottlieb tube. Alternatively, you can take the contents in a beaker.

2) Add 2 ml of ammonia.

3) Cork the rose-gottlieb tube and mix the contents by shaking, with slight warming, until the contents present an entirely homogenous appearance and are free from flakes of protein. In case the beaker is used, mix contents with a glass rod and pour contents into the separating funnel.

4) Add 10 ml of 95 per cent alcohol with further shaking.

5) Now add 18 ml of ethyl ether and mix the contents of the tube/separating funnel thoroughly by repeated inversions.

6) Add 18 ml of petroleum ether and mix again.

7) Let it stand for a few minutes till the separation of the ether solution containing fat is obtained.

8) Transfer the ether layer in a small tared/ previously weighed beaker by means of wash bottle tube. Alternatively, do the mixing of the contents in a separating funnel and separate the ether layer in a tared beaker.

9) Repeat the extraction twice with small quantities of mixture of equal parts of ethyl ether and petroleum ether and add to the main volume of ether solution.