Fats are triesters of long chain fatty acids and glycerol. One of the function of fats in the body is to provide energy. Fats provide twice as much energy as that provided by the same amount of carbohydrates.
Fats are insoluble in water. During the process of digestion, fats are hydrolyzed into simple substances, like fatty acids and glycerol which further break down into still simpler substances. Sources of fats in food are butter, ghee, cheese, milk, egg-yolk, meat, nuts, groundnut and soyabean.
Tests for Fats
1. Spot Test
When a sample containing fats is pressed or rubbed on a clean white sheet of paper, a greasy spot (translucent spot) appears.
2. Solubility Test
This test is based on the fact that fats are soluble in organic solvents like chloroform, alcohol, etc. but are insoluble in water. A small amount of the sample is mixed with a few drops of water, chloroform and alcohol in different test tubes and inferences are drawn on the basis of the miscibility and immiscibility of the sample with the water or organic solvents.
3. Acrolein Test
When a sample containing fat is heated with solid potassium bisulphate (KHSO4) in a test tube, a pungent irritating odour of acrolein is produced according to the following chemical reaction:
4. Huble’s Test (for determination of unsaturation in fats)
This test is based on the fact that greater the amount of unsturation in a fat or an oil, greater is the amount of Huble’s solution required to produce a permanent violet colour.
For this equal amount of saturated fat (cotton seed oil) and unsaturated fat or oil (linseed oil) are taken in two different test tubes and Huble’s solution is added to each test tube drop wise. The number of drops of Huble’s solution required for getting a permanent colour are counted in each case. More the number of drops of Huble’s solution, greater is the unsaturation in an organic compound.
Iodine from Huble’s solution adds up across the unsaturation sites of oil or fat giving a colourless product and a little more of iodine gives a permanent violet colour to the solution.
How To Perform Experiment
i) Spot Test
Take a food item to be tested and press or rub it on a clean white sheet of paper and hold it against light.
ii) Solubility Test
Take a small amount (50 mg) of the given sample in a test tube. Add 2-3 mL water in it and shake. Observe if it has dissolved in it. Similarly check the solubility of the compound in alcohol, and CCl4 separately.
iii) Acrolein Test
Heat a small amount (2-3 g) of sample with same amount (2-3 g) of solid KHSO4 in a test tube. Bring the mouth of the test tube near the nose and smell the gas evolved, if any, only superficially.
iv) Huble’s Test for unsaturation
Take two test tubes labelled as A and B. Add about 3-4 mL of chloroform to each test tube. Put some samples (2-3 g) of unsaturated fat (linseed oil) in test tube A and saturated fat (cotton seed oil) in test tube B.
Add Huble’s solution to each test tube drop wise and keep on adding while counting the drops, until a permanent violet colour appears in each test tube.