The amount of peroxide value of fats indicate the degree of primary oxidation and therefore its likeliness of becoming rancid. A lower number of peroxide value indicates a good quality of oil and a good preservation status. R-O-O-R peroxide value oxidize Fe2+ ions. The Fe3+ ions resulting from oxidation are grouped and form a red complex. Its colorimetric intensity, measured at 505 nm, is directly proportional to the concentration of peroxide value in the sample. Results are expressed as meqO2/Kg.