Peroxide value

The peroxide value (PV ) is a measure of the amount of peroxide functional groups of a fat or a fatty oil. It can be used as an indicator for the assessment of fat depravity.

Formation of peroxide groups in fat

Peroxides and hydroperoxides in fats may be caused by oxidation of unsaturated fatty acids with singlet oxygen 1O2 in an ene reaction. This reaction proceeds by prolonged standing in the oxygen-containing air, which is why the peroxide value is a measure of the corruption of the fat.

Specification

The peroxide value is " oxygen per kilogram of fat milli - equivalents " expressed according to DIN specification in. The number corresponds to the amount of substance of peroxide- bound oxygen atoms in millimoles per kilogram of fat. Containing 1 kg of fat, for example, 0.5 mmol peroxide groups, 2 * = 1 mmol 0.5 mmol O atoms are bound peroxide therein, as any peroxide having 2 oxygen atoms. Thus, the peroxide value of the fat is POZ = 1

Implementation

For the detection of peroxides, and determination of the peroxide has an iodine -starch reaction is carried out. Here, the sample is first treated with an acidic solution of potassium iodide in excess, wherein the iodide is oxidized to iodine by means of peroxides and hydroperoxides. When acetic acid is often used as a suitable solvent is chloroform, as it solves most fats well.

It is then combined with starch solution and back-titrated the iodine formed with thiosulfate standard solution containing a, whereby the amount of unreacted iodide can be calculated.

In parallel, a blank sample is titrated and calculated from the difference in results, the peroxide value.