The determination of the peroxide values of edible fats and oils: The iodimetric method

Abstract

AbstractFactors which influence the determination of peroxide values by the iodimetric method have been investigated. These include dissolved oxygen and moisture in the reagent, time and temperature of reaction, and amount of fat taken. The necessity for adequate de‐aëration of the reagent before admixture with the fat had been demonstrated for this, as previously for the photometric ferrous salt method, but the ratio between the “aërobic” and “anaërobic” values is much smaller for the iodimetric than for the ferrous salt method. Alternative procedures for determination of iodimetric peroxide values are recommended by (a) a “cold” method involving standing at laboratory temperature for one hour, or (b) a rapid “hot” method involving heating at the boiling point of the solvent for two minutes.The increase in apparent peroxide value observed in earlier iodimetric procedures when the quantity of fat taken for the determination was reduced, has been shown to be due to an increasing error reuniting from further oxidation of the fat by dissolved oxygen during the determination, rather than to a decreasing error due to loss of iodine by re‐absorption. In both the procedures now recommended, exclusion of atmospheric oxygen is adequate and the results, within reasonable limits, are independent of the size of the sample of fat taken.