Determination of peroxide value
Rancidity is brought about by the action of air (oxidative rancidity) or by microorganisms (ketonic rancidity) in oil. In oxidative rancidity oxygen is taken up by the fat with the formation of peroxides. The degree of peroxide formation and the time taken for the development of rancidity differ among oils.
Peroxide value is a measure of the peroxides contained in the oil. The peroxides present are determined by titration against thiosulphate in the presence of KI. Starch is used as indicator.
» Solvent Mixture: Mix two volumes of glacial acetic acid with one volume of chloroform.
» 5% Potassium Iodide Solution.
» 1% Starch Solution.
» N/500 Sodium Thiosulphate Solution. Prepare N/10 solution and dilute to N/500 on the day of use.
S = mL Na2S2O3 (Test-Blank) and
N = normality of Na2S2O3
1. Cox, H E and Pearson, D (1962) The Chemical Analysis of Foods Chemical Publishing Co Inc New York p 421.
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