Microwave heating of different commercial categories of olive oil: Part I. Effect on chemical oxidative stability indices and phenolic compounds

The effect of microwave heating of extra virgin olive oil (EVOo), olive oil (Oo) and pomace olive oil (Po) in domestic appliances,was investigated in terms of chemical oxidative indices (peroxide, p-anisidine and Totox values), free acidity, water content, total phenol content and different classes of phenolic compounds. Water content of unheated EVOo was higher as compared to the other two oils and it was found to decrease with increasing treatment time in all oils, especially in EVOo. Lipolysis was noticeable in EVOo only at highest treatment times. P-Anisidine values showed a sinusoidal trend in EVOo and Oo with a maximum at 6 and 15 min, respectively, while they gradually increased in Po. Significant amounts of phenols were detected only in unheated EVOo, even though about 30% were lost after 6 min. Among the different classes of phenolic compounds, o-diphenols and lignans displayed the highest microwave heating resistance in the whole time range of microwave application, which is of great importance from a nutritional standpoint. The utilisation of Po may be encouraged especially at short microwave treatment times for both domestic and food catering applications.