How To Detect Food Adulterants

November 2, 2008
By Syed Akbar
Adulterants, both harmful and simple, can be detected easily through small tests. These tests can be done at home too. What one needs is a set of equipment and chemicals and the culprits can be found out easily through these simple anti-adulteration tests.
Here are a few such tests as suggested by the Union Ministry of Health and Family Welfare, Government of India:

Vegetable oils:

Vegetable oils are generally mixed with castrol oil or argemone oil to make quick profits. These adulterants can be detected by the following two tests: In case of castrol oil: Take 1 ml. of vegetable oil in a clean dry test tube. Add 10 ml. of acidified petroleum ether. Shake vigorously for 2 minutes. Add 1 drop of ammonium molybdate reagent. The formation of turbidity indicates presence of castor oil in the sample.
In case of argemone oil: Add 5 ml concentrated HNO3 ¬¬to 5 ml.sample. Shake carefully. Allow to separate. Yellow, orange yellow or crimson colour in the lower acid layer indicates adulteration.

Ghee:

Ghee is generally mixed with mashed potato or sweet potato to make it weighty and creamy. Often vanaspati is also added to Ghee.
In case of mashed potato or sweet potato: Boil 5 ml. o the sample in a test tube. Cool and put a drop of iodine solution. Blue colour indicates presence of starch. Colour disappears on boiling and reappears on cooling.
In case of vanaspati: Take 5 ml. of the sample in a test tube. Add 5 ml. of hydrochloric acid and 0.4 ml of 2 per cent furfural solution or sugar crystals. Insert the glass stopper and shake for 2 minutes. Development of a pink or red colour indicates presence of vanaspati in Ghee.
Often old ghee (rancid stuff) is added. To detect this, take one teaspoon of melted sample and 5 ml. of HCL in a stoppered glass tube. Shake vigorously for 30 seconds. Add 5 ml. of 0.1 per cent of ether solution of phloroglucinol. Restopper and shake for 30 seconds and allow to stand for 10 minutes. A pink or red colour in the lower acid layer indicates rancidity.

Synthetic colours in food items:

To find out whether synthetic colouring matter is used in food items, pour 2 gms. of filtered fat dissolved in ether. Divide into 2 portions. Add 1 ml. of HCL to one tube. Add 1 ml. of 10 per cent NaOH to the other tube. Shake well and allow to stand. Presence of pink colour in acidic solution or yellow colour in alkaline solution indicates added colouring matter.

Honey:

Honey is good for health and it has several curative properties. But honey is generally adulterated with invert sugar or jaggery. There are two tests to find out whether the honey in question is pure or adulterated.
Fiehe’s Test: Add 5 ml. of solvent ether to 5 ml. of honey. Shake well and decant the ether layer in a petri dish. Evaporate completely by blowing the ether layer. Add 2 to 3 ml. of resorcinol (1 gm. of resorcinol resublimed in 5 ml. of concentrated HCL.). Appearance of cherry red colour indicates presence of sugar/jaggery.
Aniline chloride Test: Take 5 ml. of honey in a porcelain dish. Add aniline chloride solution (3 ml of aniline and 7 ml. of 1:3 HCL) and stir well. Orange red colour indicates presence of sugar.

Pulses and Besan:

Besan atta or pulses are adulterated with Kesari dal (Lathyrus sativus). To find out the adulterant, add 50 ml. of diluted HCL to a small quantity of dal and keep on simmering water for about 15 minutes. The pink colour, if developed, indicates the presence of Kesari dal.
Pulses are also adulterated with metanil yellow dye. To find this out, add concentrated HCL to a small quantity of dal in a little amount of water. Immediate development of pink colour indicates the presence of metanil yellow and similar colour dyes.
To find out whether lead chromate is used in the pulses, shake 5 gm. of pulses with 5ml. of water and add a few drops of HCL. Pink colour indicates lead chromate.

Wheat flour or atta:

Atta is generally contaminated with excessive sand and dirt. Shake a little quantity of sample with about 10 ml of carbon tetrachloride and allow to stand. Grit and sandy matter will collect at the bottom.
Often chalk powder is used in atta. To find out, shake sample with diluted HCL. Effervescence indicates chalk

Common spices:

Common spices like turmeric, chilly and curry powder are also adulterated by colours.
Extract the sample with petroleum ether and add 13N H2SO4 to the extract. Appearance of red colour (which persists even upon adding little distilled water) indicates the presence of added colours. However, if the colour disappears upon adding distilled water the sample is not adulterated.
Spices (ground) are adulterated by red bran and saw dust. Sprinkle on water surface. Powdered bran and sawdust float on the surface.
Coriander powder is adulterated with dung powder. To find out, soak in water. Dung will float and can be easily detected by its foul smell.

Chillies:

Brick powder, grit, sand, dirt, filth, etc are used in chillies, especially chilli powder. Pour the sample in a beaker containing a mixture of chloroform and carbon tetrachloride. Brick powder and grit will settle at the bottom.

Turmeric:

Lead chromate is used to give turmeric its natural color. Ash the sample. Dissolve it in 1:7 sulphuric acid (H2SO4) and filter. Add 1 or 2 drops of 0.1 per cent dipenylcarbazide. A pink colour indicates presence of lead chromate.

Cumin seeds:

Grass seeds coloured with charcoal dust is used. Rub the cumin seeds on palms. If palms turn black adulteration in indicated.

Asafoetida (Heeng):

Items like soap stone and other earthy matter is used for adulteration. Shake a little quantity of powdered sample with water. Soap stone or other earthy matter will settle at the bottom.
In case chalk is used as an adulterant, shake sample with carbon tetrachloride (CCl4). Asafoetida will settle down. Decant the top layer and add diluted HCL to the residue. Effervescence shows presence of chalk.

Foodgrains:

Foodgrains contain hidden insect infestations. To test the adulterants, take a filter paper impregnated with ninhydrin (1 per cent in alcohol). Put some grains on it and then fold the filter paper and crush the grains with hammer. Spots of bluish purple colour indicate presence of hidden insect infestation.