Important Tests
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Test for detection of urea in Milk
1. Urea is generally added in the preparation of synthetic milk to raise the SNF value.
Five ml of milk is mixed well with 5 ml paradimethyl amino benzaldehyde (16%). If the solution turns yellow in colour, then the given sample of milk is added with urea.
2. Take 5 ml of milk in a test tube and add 0.2 ml of urease (20 mg / ml). Shake well at room temperature and then add 0.1 ml of bromothymol blue solution (0.5%). Appearance of blue colour after 10-15 min indicates the adulteration milk with urea.
Test for detection of starch
Addition of starch also increases the SNF content of milk. Apart from the starch, wheat flour, arrowroot, rice flour are also added.
How to detect?
Take 3 ml milk in a test tube and boil it thoroughly. Then milk is cooled to room temperature and added with 2 to 3 drops of 1% iodine solution. Change of colour to blue indicates that the milk is adulterated with starch.
Test for detection of formalin
Formalin (40%) is poisonous though it can preserve milk for a long time.
How to detect?
Take 10 ml of milk in test tube and 5 ml of conc. sulphuric acid is added on the sides of the test tube with out shaking. If a violet or blue ring appears at the intersection of the two layers, then it shows the presence of formalin.
Detection of Neutralizers in milk
1) Rosalic acid test (Soda Test)
In milk neutralizers like hydrated lime, sodium hydroxide, sodium carbonate or sodium bicarbonate are added which are generally prohibited.
How to detect?
Take 5 ml of milk in a test tube and add 5 ml alcohol followed by 4-5 drops of rosalic acid. If the colour of milk changes to pinkish red, then it is inferred that the milk is adulterated with sodium carbonate / sodium bicarbonate and hence unfit for human consumption.
This test will be effective only if the neutralizers are present in milk. If the added neutralizers are nullified by the developed acidity, then this test will be negative. In that case, the alkaline condition of the milk for the presence of soda ash has to be estimated.
How to proceed?
2) Take 20 ml of milk in a silica crucible and then the water is evaporated and the contents are burnt in a muffle furnace. The ash is dispersed in 10 ml distilled water and it is titrated against decinormal (N/10) hydrochloric acid using phenolphthalein as an indicator. If the titre value exceeds 1.2 ml, then it is construed that the milk is adulterated with neutralizers.
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Tests to detect adulteration in ghee
1. Butyrorefractometer reading
Properly filtered ghee whose temperature is around 40°C is taken; 2-3 drops of it are poured in to the butyrorefractometer by the side of the glass rod. Now the reading is noted by the scale placed above the meter. Care has to be exercised to maintain the temperature of water that is flowing over the thermometer to be at 40°C. If the temperature deviates, then the results obtained may not be accurate.
2. Baudoin Test (Detection of adulteration of ghee with vanaspathi)
As per the prevention of food adulteration act, it has been made mandatory to add 5% sesame oil to vanaspathi in order to detect the presence of vanaspathi in ghee through Baudoin test. The principle behind the test is development of permanent crimson red colour with furfural in the presence of concentrated hydrochloric acid in ghee adulterated with vanaspathi.
How to detect?
Take 5 g of molten filtered ghee in a test tube and add 5 ml of concentrated hydrochloric acid and 0.1 ml furfural solution in alcohol (2%) and mix the contents thoroughly and it is allowed to remain undisturbed for 10 min. Development of crimson red colour shows that the ghee is adulterated with vanaspathi.
3. Detection of mineral oil in ghee
About 2 g of ghee is saponified with 25 ml of 50% alcoholic potassium hydroxide for one hour. Then the saponified content is transferred to a beaker containing 100 ml of water. Development of turbidity indicates the adulteration of mineral oil in ghee.
