Lipid peroxidation by Ferric thiocyanate method (Mistuda et al., 1996)
Cell membrane is more susceptible to free radicals that reacts rapidly with the unsaturated fatty acids (like linoleic acid and arachidonic acid) embedded in the membrane resulting in lipid peroxidation. In this assay, linoleic acid is used as the model system for measuring the levels of lipid peroxidation. This was used to determine the amount of peroxide formed during the lipid peroxidation, in which peroxide will react with ferrous chloride and form ferric ions. Ferric ions will then unite with ammonium thiocyanate and produce a ferric thiocyanate complex whose colour is measured at 500nm. A mixture containing 10 ml of 0.05 M-phosphate buffer (pH 7.0), 5.9ml of water, 0.1 ml of plant extract and 4 ml of 2.5% linoleic acid in absolute ethanol was placed in a vial with a screw cap and then placedin a dark oven at 40 degree centigrade overnight. To 0.1ml of this incubation mixture, added 9.7ml of 75% ethanol and 0.1 ml of 0.02M ferrous chloride in 3.5% HCl. Add 0.1ml of 30% ammonium thiocyanate, precisely 3 minutes after the addition of ferrous chloride. The absorbance of the red colour was measured at 500nm. A mixture without the plant sample was used as the negative control. (Note: Instead of plant extract, use 0.1 ml of water/ethanol/ petroleum ether as control).