Microwave Heating Induces Oxidative Degradation of Extra Virgin Olive Oil

Heating vegetable oil in a microwave oven can lead to the formation of reactive free radicals, which are responsible for causing lipid oxidation. The thermo-oxidative stability of olive oil has previously been studied under microwave heating for short processing periods that simulate typical cooking times. This study compares the effect of the oxidative degradation of extra virgin olive oil (EVOO) during extended heating times under different microwave powers (150 and 500 W) or conventional heating. The results showed that intense microwave heating of EVOO significantly increased the free acidity and specific extinction coefficients (K270), and resulted in more severe loss of phenolic compounds, compared with conventional heating. Microwave treatment also resulted in higher amounts of acrolein in EVOO after a short processing period compared with conventional heating. These results demonstrate that intene microwave heating has a more severe effect on EVOO compared with conventional heating.