In general, metal ions are known to increase the oxidation of vegetable oil. The presence of metal ions was reported to increase the formation of formaldehyde, acetaldehyde, propanal, and heptenal in the heated oil. The effect is highest for copper ions followed by iron and aluminium . Both copper and iron ions showed prooxidative catalytic effects in olive oil, though the impact of copper was again more pronounced. This was found by a Rancimat experiment at 110 ℃ on olive oil spiked with Cu(II)-and Fe(III)-cyclohexanebutyrates . The addition of ferric stearate in partially hydrogenated soybean oil was reported to decrease its thermoxidative stability. These results were obtained by heating the oil at various temperatures between 120 to 200 ℃. The amount of iron added to the oil ranges between 0.5 and 1.2 mg iron per kg of oil . In a comparable study, heme iron was incorporated into partially hydrogenated soybean oil at a concentration of 2.7 ppm. The modified oil also showed poor stability when subjected to heating within the temperature range of 160 to 200 °C over a duration of 72 hours.