Iodine value of an edible oil
Fats and oils known as triglycerides contain long chain hydrocarbons with carboxyl groups (COOH groups). These fatty acids are classified into the number of double bonds present in the fatty acid.
When the carbon atoms in these chains are bounded to the maximum possible number of hydrogen atoms, the triglyceride is said to be saturated. When one or more double bonds exist between carbon atoms in the chain, less hydrogen exists within the molecule and the fat is said to be unsaturated. Unsaturated fatty acids can be converted into saturated by the process of hydrogenation. Halogens such as iodine combine with the double bonds. The amount of iodine reacted is proportional to the degree of unsaturation within the molecule. This value is known as the iodine value.
The iodine value of a fixed oil is the weight of iodine absorbed by 100 parts by weight of the substance when determined by a standard method. Knowing the iodine value is useful in providing a means of comparison of oils. The more iodine attached, the higher is the iodine value and the more reactive, less stable, softer (liquid), long shelf life and more susceptible to oxidation and rancidifaction of the oil or fat.
To determine the iodine value in the given oil sample 344 and thus estimate the degree of unsaturation present
Accurately weigh 3-4 drops (about 0.15 – 0.2 g) of the oil sample into a clean, dry 250 mL iodine flask.
To the oil in the iodine flask, add 10 mL of dichloromethane acting as a solvent and mix by swirling gently.
Add 20 mL of iodine monochloride solution from a burette and mix. Then add about 5 mL of a 2.5% solution of mercuric acetate in glacial acetic acid, which will act to catalyse the reaction. Insert the stopper which has been previously moistened with a solution of potassium iodide.
Keep in a dark place for 3 minutes to allow the unsaturated fatty acid residues of the