Tests for Detecting Adulteration in Food
The adulterants present in different food items can be easily identified by simple tests described below:
1. Vanaspati in Ghee or Butter:
Take small amount of desi ghee or butter in test-tube. Heat the test-tube to melt the ghee. Add to an equal amount of conc. HCl and a small amount of sugar. Shake the contents vigorously for a minute and allow the tube to stand for about five minutes. Appearance of crimson color in the lower acid layer shows that vanaspati ghee has been mixed as an adulterant to desi ghee.
2. Paraffin wax and Hydrocarbons in Vanaspati Ghee:
Heat small amount of vanaspati ghee with acetic anhydride. Droplets of oil floating on the surface of unused acetic anhydride indicate the presence of wax or hydrocarbon.
3. Argemone oil in Edible oil:
To small amount of oil in a test-tube, and few drops of conc. HNO3 and shake. Appearance of red color in the acid layer indicates presence of argemone oil.
4. Brick powder in red chilli powder:
Add small amount of chili powder in beaker containing water. Brick powder settles at the bottom while pure chili powder floats over water.
5. Metanil Yellow in Dal:
Take about 5 g of dal in a test-tube and add about 5 ml of water to it. Shake the contents well and add a few drops of hydrochloric acid (HCl). Appearance of pink color indicates the presence of metanil yellow.
6. Lead chromite in Turmeric Powder:
Take a small amount of sample turmeric powder in a test-tube and add to it dil. HNO3. Filter and filterate add a few drops of potassium iodide solution. Appearance of yellow precipitate indicates the presence of lead salts as adulterant.
7. Water in Milk:
The presence of water in milk can be tested by the following two tests:
(i) Pure milk is thick but when it is adulterated with water its viscosity decreases. It becomes thin and flows easily. So to check the adulteration of milk with water, put a drop of milk sample on the surface of a vertically held glass plate. If the drop of milk either stays on the surface or moves down slowly leaving a white trail behind it then it shows that the milk sample is pure and is not adulterated with water. If on the other hand, the milk sample readily flows down then it shows that the milk sample is adulterated with water. However, this test cannot be applied to test the adulteration of skimmed milk (the milk from which cream has been removed) with water. For skimmed milk, a device called lactometer is used to test the purity of milk.
(ii) The relative density of pure milk is 1.026. On adding water to pure milk, the relative density of pure milk decreases and this can be detected by using a lactometer. Lactometer is a cylindrical device that measures the density of the fluid. It has markings of relative density values on it. When the lactometer tube is put in the sample of milk taken in a cylinder it starts floating in it. The relative density value in level with the surface of milk gives the relative density of milk. For a milk sample, which is adulterated with water the relative density, value comes out to be less than 1.026.