How to Check Adulteration in Milk

Maneka Gandhi

(Bihar Times) Since you will not stop drinking milk – and since 70 -100% of the milk has been adulterated with very dangerous adulterants according to Food Safety Standards Authority of India FSSAI, you should learn how to make out real milk from synthetic. Milk samples from all over the country were checked for fat (%), SNF (%), neutralizers, acidity, hydrogen peroxide, sugar, starch, glucose , urea, salt, detergents, skimmed milk powder, formalin and vegetable fat. Most of the samples were found to be adulterated.

This is how synthetic milk is made: Vegetable refined oil is taken in a wide mouthed container along with a suitable emulsifier and thoroughly mixed till it becomes a thick white paste. Water is slowly added to the paste until the density of the liquid is similar to that of milk. Then is added urea or sodium sulphate or glucose or maltose or sometimes any one of the commonly available fertilizers after dissolving in hot water. The refined oil in synthetic milk acts as a source of fat whereas the hot solution of any one of the substances above mentioned acts as a source of solids not fat (SNF). The ingredients that go in to the making of synthetic milk are calculated in such a way that the fat and SNF percentage is similar to mixed milk. Hence it easily passes the tests carried out at the village level dairy co-operative society (fat and lactometer reading etc.) This is the difference between real and synthetic milk. The colour of both is white. But while on storage real milk remains white, synthetic milk or adulterated milk turns pale yellow. If rubbed on the palm, synthetic milk becomes foamy. Real milk does not. Real milk does not change colour on heating. Synthetic milk turns yellow on boiling. The pH value of real milk is 6.6 – 6.8 and of synthetic milk 10-11 (extremely alkaline). The fat content is the same in both: 4.5 – 5 %, the SNF (Solid Not Fat) is also the same 8-9%.

Here are some methods to detect adulteration:  1. Detection of Neutralizers in milk-  Rosalic acid test (Soda Test). Neutralizers like hydrated lime, sodium hydroxide, sodium carbonate or sodium bicarbonate are added to milk. 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 the milk is adulterated with sodium carbonate / sodium bicarbonate and unfit for human consumption.

2. The alkaline condition of the milk for the presence of soda ash. Take 20 ml of milk in a silica crucible. Evaporate the water and burn the contents 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.

3. Detection of hydrogen peroxide. Take 5 ml milk in a test tube and then add 5 drops of paraphenylene diamine and shake it well. Change of the colour of milk to blue confirms that the milk is added with hydrogen peroxide.

4. Test for detection of formalin. Formalin (40%) is poisonous. It is added because it can preserve milk .Take 10 ml of milk in test tube and add 5 ml of concentrated sulphuric acid on the sides of the test tube without shaking. If a violet or blue ring appears at the intersection of the two layers, then it shows the presence of formalin.

5. Test for detection of sugar in milk. Sugar is mixed in milk to increase the solids not fat content of milk. It increases the lactometer reading of water diluted milk. Take 10 ml of milk in a test tube and add 5 ml of hydrochloric acid along with 0.1 g of resorcinol. Shake the test tube well and place it in boiling water for 5 min. Appearance of red colour indicates the presence of added sugar in milk.

6. 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. Take 3 ml milk in a test tube and boil it thoroughly. Cool the milk to room temperature and add 2 to 3 drops of 1% iodine solution. Change of colour to blue indicates that the milk is adulterated with starch.

7. Test for detection of glucose. Usually poor quality glucose is added to milk to increase the lactometer reading. There are two tests available to detect the adulteration of milk with glucose. Take 3 ml of milk in a test tube and add 3 ml Barford’s reagent and mix it thoroughly. Keep it in boiling water for 3 min and cool for 2 min by immersing in tap water. Add 1 ml of phosphomolybdic acid and shake. If blue colour is visible, then glucose is present. Take a strip of diacetic and dip it in the milk for 30 sec to 1 min. If the strip changes colour, then it shows that the sample of milk contains glucose. If there is no change in the colour of the strip, then glucose is absent.

  8. Test for detection of urea. Urea is added 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 milk is contaminated. 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 adulteration.

9. Test for detection of ammonium sulphate. Sulphate in milk increases the lactometer reading. Put 5 ml of hot milk in a test tube and add citric acid . The whey will separate. Collect the whey in another test tube and add 0.5 ml of 5% barium chloride. A precipitate indicates the presence of ammonium sulphate.

10. Test for detection of salt. Addition of salt increases the lactometer reading. Take Five ml of silver nitrate (0.8%) in a test tube and add 2 to 3 drops of 1% potassium dichromate and 1 ml of milk and mix. If the contents turn yellow in colour, then milk contains salt in it. If it is chocolate coloured, then the milk is free from salt.

11. Test for detection of pulverized soap. Take 10 ml of milk in a test tube and dilute it with equal quantity of hot water and then add 1 – 2 drops of phenolphthalein indicator. A pink colour indicates soap.

12. Detection of detergents in milk. Take 5 ml of milk in a test tube and add 0.1 ml of bromocresol purple solution. A violet colour indicates detergent in milk. Unadulterated milk samples show a faint violet.

13. Detection of skim milk powder in milk. If the addition of nitric acid drop by drop in to the milk sample results in an orange colour, it indicates skim milk powder. Pure milk shows yellow colour.

14. Detection of benzoic and salicylic acid in milk. Five ml of milk is taken in a test tube and acidified with concentrated sulphuric acid. 0.5% ferric chloride solution is added drop by drop and mixed well. A buff colour indicates benzoic acid and violet colour indicates salicylic acid.

15. Detection of borax and boric acid in milk. Add 1 ml of concentrated hydrochloric acid to five ml of milk in a test tube and mix well. Dip the tip of a turmeric paper into the acidified milk and dry in a watch glass at 100°C or over a small flame. If the turmeric paper turns red, it indicates the presence of borax or boric acid. Or add a drop of ammonia solution on the turmeric paper. If the red colour changes to green, it shows boric acid. 

If I were a business person, I would start marketing home chemical kits for milk testing: chemicals, lactometer, test tubes, droppers, gas burner, measuring cylinders, beakers and bottles. If I were a school chemistry teacher, I would make my students bring milk from home and test once a week. As a householder I would – and have – simply ban milk from the house.

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