Detection of Adulteration in Milk
Adulteration in milk considerably reduces the quality of milk. Soap, acid, starch, table
sugar and chemicals like formalin are some of the adulterants added to milk. Most of
the chemicals used as adulterants are poisonous and can cause health hazards.
Here are some tests to find out some of the common adulterants in milk.
Materials Required Milk
Methylene blue Test tubes
Water bath Concentrated HCl
Resorcinol Iodine solution
Concentrated Sulphuric acid 0.5% Ferric Chloride solution
Phenolphthalein indicator Hot water
2% Sodium hydroxide 2% Sodium hypochlorite
5% phenol Procedure
Arrange the required materials on the lab table. Detection of Table Sugar in Milk
Pour 10 ml of milk into the test tube labelled “Table Sugar” and using a pipette add
Concentrated HCl into the tube. This should be done in the Fume Hood.
Now shake the test tube gently so that the milk gets precipitated.
Weigh 100milli gram of Resorcinol and add this to the precipitated milk. Then shake
the test tube well. The colour of the milk solution changes to light brown.
Now place the test tube with the test tube holder in a water bath at 1000C for 5 minutes.
The colour of the milk solution turns red, which shows the presence of table sugar in
milk. If the colour remains the same it denotes the absence of table sugar in milk. Detection of starch
Pour 3 ml milk in a test tube labelled “Starch”. Now place the test tube with the test tube
holder in a water bath at 100 C. After 5 minutes remove the tube from the water
bath and allow it to cool. Using a dropper add 2-3 drops of Iodine solution
to the test tube and shake it well. If the colour of the milk solution turns yellow,
it indicates the absence of starch. Dark blue colour indicates the presence of starch in
milk. Detection of Benzoic Acid and Salicylic acid Pour 5 ml milk from the beaker into the test
tube labelled “Acid“. Add few drops of conc. Sulphuric acid into
the milk and shake the test tube gently. This should be done in the Fume Hood.
You will observe that the milk is getting precipitated. Now, using a dropper add 0.5%
ferric chloride solution drop by drop and mix this well.
A Buff colour indicates the presence of Benzoic acid. If you observe a violet colour it shows
the presence of salicylic acid in the milk. Detection of Soap
Pour 10 ml milk into a test tube labelled “Soap”. Then add 10 ml hot water to the
milk. Add 1-2 drops of phenolphthalein indicator
into the test tube and mix this gently. If the colour turns pink, it indicates the
presence of soap in the milk. If the colour remains the same it shows the absence of soap
in milk. Detection of Formalin in milk
Pour 2 ml milk into a test tube labelled “Formalin”. To this add 2 ml of 90% sulphuric acid containing
Ferric Chloride using a glass pipette. This step should be done in the Fume Hood.
A purple violet ring formed at the junction indicates the presence of Formalin in the
milk. Detection of Ammonium sulphate in milk
Pour 1 ml milk into a test tube labelled “Ammonium Sulphate”.
Pipette out 500 micro litre of 2% NaOH solution and add this to the test tube. Discard the
used tip and insert a new tip. Pipette out 500micro litre of 2% Sodium Hypochlorite and
add this to the milk solution. You will notice that the colour has turned
light yellow. Insert a fresh tip and add 500micro litre
phenol solution and mix this well. The milk solution turns light bluish colour.
Keep this test tube in water bath at 100 C for 20 Seconds.
After 20 seconds the colour turns deep blue indicating the presence of Ammonium sulphate.
If the solution turns pink, it indicates the absence of ammonium sulphate. Detection of Micro-Organisms in milk
Pour 10 ml milk from the beaker into the test tube labelled “Micro-Organism”.
Add 8-10 drops of methylene blue into the test tube containing milk and mix the contents
well. The colour of the milk solution turns blue.
Close the test tube using cotton ball and keep it in the incubator for 30 minutes at
37 C. If the blue coloured milk solution turns white
immediately, it indicates a larger count of micro-organism in the milk. If the colour
remains the same, it indicates the presence of fewer numbers of microorganisms in the