Effect of heating on chemical parameters of extra virgin olive oil, pomace olive oil, soybean oil and palm oil.

This work studied the oxidative stress on the chemical properties of extra virgin olive oil, pomace olive oil, soybean oil and palm oil during heating. The highest relative increase in free acidity was found in pomace olive oil. Peroxide value as an absolute value (meq O2/kg) was lowest in palm oil 1.4 (unheated), 4.0 (180°C - 120 min), 6.4 (220°C - 120 min). Extra virgin olive oil had lower spectrophotometric indices (K232, K270 and ΔK) compared to the solvent extracted oils. Total phenols were highest in the extra virgin olive oil (196.8 mg/kg) and decreased to 59.8 and to 66.8 mg/kg after 120 min of heating at 180°C and 220°C respectively. A decreasing trend was also found in the tocopherol content with the highest % reduction (-79.5%) in EVOO heated at 220°C for 120 min. This was in agreement with the antioxidant activity trend measured with the ABTS assay (2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) (155.9 microM TE/100 g) and with the oxygen radical absorbance capacity (ORAC) assay (316.1 "M TE/100 g) in the unheated extra virgin olive oil.