Food adulteration has been a growing concern all over the world. One of the most common food commodities adulterated with fatal chemicals is milk, which is consumed by millions of people every day. Henceforth, consumers must be aware of what they consume. To test whether the milk we receive every day is safe to consume, we can carry home-based rapid adulterant detection tests.
Once suspicious, individuals should go for an adulteration test in a milk testing laboratory. During milk tests in labs, the following given methods are generally used.
Detection of Vanaspati-
Take 3 ml of milk in a test tube.
Add 10 drops of Hydrochloric Acid (HCl).
Mix one teaspoonful of sugar.
After 5 minutes, examine the mixture.
The red coloration indicates the presence of vanaspati in the milk.
Detection of Formalin-
Formalin is used in laboratories to preserve milk for testing purposes. However, it is highly toxic when consumed, and leads to liver and kidney damage. Formalin adulteration is found in milk, and can be detected by the following method-
Take 10 ml of milk in a test tube and add 5 ml of concentrated Sulfuric acid (H2SO4) from the sides of the wall without shaking.
If a violet or blue ring appears at the intersection of two layers then it shows the presence of formalin.
Detection of Ammonium Sulphate-
Ammonium Sulphate is an adulterant used in milk to maintain the density of milk even when water is added. Its presence can be detected as follows-
Take 5 ml of hot milk in a test tube.
Add a suitable acid, e.g., Citric Acid.
The whey obtained is separated and filtered.
Take the whey in another test tube and add 0.5 ml of 5% Barium Chloride.
The appearance of a precipitate indicates the presence of Ammonium Sulphate.
Or,
Take 5 ml of milk in a test tube.
Add 2.5 ml of 2% Sodium Hydroxide, 2.5 ml of 2% Sodium Hypochlorite, and 2.5 ml of 5% Phenol Solution.
Heat for 20 seconds in a boiling water bath.
If the bluish color turns to deep blue, it indicates the presence of Ammonium Sulphate.
However, in case it turns pink, it shows that the sample is free from Ammonium Sulphate.
Detection of Salt-
Take 5 ml of Silver Nitrate reagent in a test tube.
Add 2-3 drops of Potassium Dichromate Reagent.
Add 1 ml of milk to the above test tube and mix thoroughly.
If the contents of the test tube turn yellow, then milk contains salt.
If it turns to chocolate color or reddish-brown, the milk sample is free from salt
Detection of Hydrogen Peroxide-
Take 5 ml milk in a test tube.
Add 3 drops of Paraphenylene Diamine and shake well.
The change in color of the milk to blue confirms that the milk is adulterated with Hydrogen Peroxide Or,
To 10 ml of milk sample in a test tube, add 10-15 drops of Vanadium Pentoxide reagent and mix.
Pink or red color indicates the presence of Hydrogen Peroxide.
Detection of Sugar-
The sugar present in milk is lactose. When table sugar is added, the density of milk increases, after which the fraudsters add water to the milk, henceforth, deceiving the lactometer reading. When resorcinol is added, it reacts with ketose sugar to form a red-colored precipitate, which indicates the adulteration of table sugar in milk.
Take 3 ml of milk in a test tube.
Add 2 ml of hydrochloric acid. Heat the test tube after adding 50 mg of resorcinol.
The red coloration indicates the use of sugar in the milk.
Detection of Sodium Bicarbonate/ Neutralizer-
Take 3 ml of milk in a test tube and add 5 ml of rectified spirit to it.
Then add 4 drops of Rosalic acid solution.
The appearance of red/rosy coloration indicates the presence of Sodium bicarbonate in the milk.
Detection of Boric acid-
Take 3 ml of milk in a test tube.
Add 20 drops of hydrochloric acid and shake the test tube or mix up the contents thoroughly.
Dip a yellow paper strip and remove the same after 1 minute.
A change in color from yellow to red, followed by the change from red to green by the addition of one drop of ammonia solution, indicates that the boric acid is present in milk
To prepare the yellow paper strip, dip strips of filter paper in an aqueous solution of the turmeric, and dry it up.
Removal of fat- The Lactometer reading will go above 26. However, the milk will remain thick.
For detection of vanaspati in sweet curd:
Take 1 teaspoon full of curd in a test tube.
Add 10 drops of hydrochloric acid.
Mix up the contents shaking the test tube gently.
After 5 minutes, examine the mixture.
The red coloration indicates the presence of vanaspati in the curd.
For blotting paper in Rabri:
Take a teaspoon of rabri in a test tube.
Add 3 ml of hydrochloric acid and 3 ml of distilled water.
Stir the content with a glass rod.
Remove the rod and examine.
The presence of fine fibers on the glass rod will indicate the presence of blotting paper in rabri.
Coal Tar Dyes in Ghee, cottage cheese, condensed milk, khoya, milk powder, etc.-
Add 5 ml of dilute Sulphuric Acid or concentrated Hydrochloric Acid to one teaspoon full of product sample in a test tube.
Shake well. Pink color (in case of dilute Sulphuric acid) or crimson color (in case of concentrated Hydrochloric Acid) indicates the presence of coal tar dyes.
If Hydrochloric Acid does not give color, dilute it with water to get the color to see the result.
Detection of vanaspati/margarine in Ghee-
Take about one teaspoon full of the melted sample of ghee with an equal quantity of concentrated Hydrochloric acid in a test tube with a stopper and add to it a pinch of sugar.
Shake for one minute and let it stand for five minutes, Appearance of crimson color in the lower (acid layer) indicates the presence of vanaspati or margarine.
The test is specific for sesame oil which is compulsorily added to vanaspati and margarine. • Some coal tar dyes also give a positive test. • If the test is positive i.e. Red color develops only by adding Strong Hydrochloric acid (without adding crystals of sugar) then the sample is adulterated with coal tar dye. If the crimson or red color develops after adding and shaking with Sugar, ensure the presence of vanaspati or margarine only.
These were some of the common laboratory tests, that are used to test the presence of any adulterants in milk and milk products. Since the cases of adulteration are increasing day by day, the consumers must be aware and responsible enough to be able to protect themselves from consuming these poisons.
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