Oxidative stability of olive, corn and soybean oil under different conditions

To follow the relative rates of oxidative deterioration in edible oils, refined olive, corn and soybean oils were analyzed periodically for their peroxide value (PV), p-anisidine value (p-AV) and iodine value (IV), following exposure to air or air-light for 30 days. Changes in the above values of the oils were also examined and after their use for deep-frying of French fries at 180 °C for varying periods of time, namely 30, 60 and 90 min. PV and p -AV values increased in the order: deep-frying > air-light exposure > air exposure while the values with respect to the oils increased in the order: soybean > corn > olive. Decrease in IV followed the same pattern, i.e. deep-frying > air-light > air and soybean > corn > olive. Deep-frying of French fries in corn oil was also carried out in the presence of caffeic, ferulic, vanillic acid and crude tea extract as antioxidants. All antioxidants effectively reduced the oxidation rate in the oil, as detected by decrease in PVs and p -AVs and relatively low reduction rate in IVs for all the frying times. The order of antioxidative activity was caffeic acid > vanillic acid > ferulic acid > tea extract.