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Detection of peroxide gives the initial evidence of rancidity in unsaturated fats and oils. Other methods are available, but peroxide value is the most widely used. It gives a measure of the extent to which an oil sample has undergone primary oxidation; extent of secondary oxidation may be determined from p-anisidine test.Chemistry And Technology Of Oils And Fats Chemistry And Technology Of Oils And Fats By Dr. M.M. Chakrabarty
The found in fats and oils play a role in autoxidation. Oils with a high degree of Unsaturated fat are most susceptible to autoxidation. The best test for autoxidation (oxidative rancidity) is determination of the peroxide value. are intermediates in the autoxidation reaction.
Autoxidation is a free radical reaction involving oxygen that leads to deterioration of fats and oils which form off-flavours and off-odours. Peroxide value, concentration of peroxide in an oil or fat, is useful for assessing the extent to which spoilage has advanced.
The base produced in this reaction is taken up by the excess of acetic acid present. To measure the iodine, a redox titration is performed using sodium thiosulfate.
The acidic conditions (excess acetic acid) prevents formation of hypoiodite (analogous to hypochlorite), which would interfere with the reaction.
A starch indicator solution is used, for which amylose forms a blue to black solution with iodine and is colorless when the iodine is converted to iodide Redox titration.
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