Effect of microwave heating with different exposure times on physical and chemical parameters of olive oil.

This study reflects the effect of different microwave heating times (1, 3, 5, 10 and 15 min) on physical and chemical characteristics of three Portuguese olive oils from three protected designation of origin (PDO), "Azeite de Trás-os-Montes PDO", "Azeites da Beira Interior PDO", and "Azeite de Moura PDO". The parameters evaluated were free acidity, peroxide value, specific extinction coefficients (K232 and K270), color and chlorophylls and carotenoids content. A differential pulse voltammeter was also used to monitor the changes in alpha-tocopherol content. The results showed that microwave heating produce losses in the quality of the different analysed olive oils. The heating time did not promote the occurrence of hydrolysis in the samples since no changes in free acidity values were found. All other parameters were affected by exposure time in a similar way: in the first 3 min no marked changes were observed, after that the quality of the oil decrease significantly. The microwave heating time also affects the total chlorophylls, carotenoids and alpha-tocopherol contents which clearly decreased as long as the exposure time increases. After 15 min of heating the electrochemical signal, due to the alpha-tocopherol, disappear completely in the voltamogram.