Direct analysis of total antioxidant activity of olive oil and studies on the influence of heating

Aim of this study was to evaluate the total antioxidant activity (TAA) of e xtra virgin olive oil (EVOO) and the effect of heating on the alpha -tocoph erol content and TAA in relation to the presence of polyphenols, heating ti me, and temperature. Experiments included the measurement by ABTS decoloriz ation assay of antioxidant capacity of alpha -tocopherol and 14 simple phen olic compounds present in EVOO, either dissolved in ethanol or added to ref ined olive oil, and the evaluation of TAA, total phenols, and alpha -tocoph erol of six commercial EVOO and three olive oils. Finally, four experimenta l oils were prepared from refined olive oil containing a fixed amount (300 ppm) of alpha -tocopherol and increasing amounts of polyphenols (25, 125, 2 25, and 326 ppm) extracted from EVOO. The thermal stability of experimental oils under domestic heating conditions (heating time from 30 to 120 min; h eating temperature from 160 to 190 degreesC) was studied bg evaluating the loss of alpha -tocopherol and TAA according to a Latin square design. Resul ts indicate that TAA of commercial oils is mainly due to their phenol and a lpha -tocopherol content. Heating experiments suggest that polyphenols from EVOO are effective stabilizers of alpha -tocopherol during olive oil heati ng, thus contributing. to the nutritional value of cooked foods.