Coconut oil is the most common cooking medium in Kerala. Since its price is now on an escalating spiral, lot of adulterants are added to it - like base oil, paraffin oil, palm oil and the like. How to detect presence of additives in the coconut oil we consume? Here is a simple test and other elaborate chemical tests recommended for detection.
Simple test
Place a small bottle of oil in refrigerator. Coconut oil solidifies leaving the
adulterant as a Separate layer.
Chemical tests on edible oils in general
1. Detection of Mobil oil
Take a little amount (20 drops) of the sample in a test tube. Add 10 drops of alcoholic potash. Heat the tube on the flame of a spirit lamp to decolourize the mixture. Add 10 drops of dichloroquinol chloride. Heat the tube again. The appearance of blue colour indicates the presence of a compound of triorthocrysyle phosphate (TOCP) which contributes to incidence of paralysis. Traces of this compound in edible oil to an admixture of edible oil with mobil oil.
2. Rancidity
Take a little amount (3 ml) of the sample in a test tube. Add in it 3 ml of hydrochloric acid. Plug the mouth of the test tube. Shake the tube to mix up the contents thoroughly. Add 3 ml of 0.1% phloroglucinol solution in ether. Shake the tube vigorously for 2 minutes and keep it aside. Examine the tube after half an hour. A red or pink colouration in acid layer indicates that the oil sample in rancid.
3. Cyanide
Take a little amount (3 ml) of the sample in a test tube. Add 10 drops of alcoholic potash and heat the tube on the flame of a spirit lamp. Make an addition of a little amount of each of ferrous sulphate and ferric chloride in the test tube and shake it to mix up the contents thoroughly. Add 3 ml of hydrochloric acid. A blue colouration indicates the presence of hydrocyanic acid which gets produced due to presence of cyanide in edible oil.
4. Prohibited Colour
Take a little amount (20 drops) of the sample in each of 4 test tubes. Prepare 3 different solutions, mixing up 1 part of distilled water, 3 parts of distilled water and 4 parts of distilled water. Add 2 ml of each solution in each of 3 test tubes and add 2 ml of hydrochloric acid in the fourth test tube. Shake each tube to mix up the contents thoroughly. A rosy colouration in the mixture of any tube indicates the presence of prohibited colour in edible oil.
