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a-tocopherol a b s t r a c tThis 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 (K 232 and K 270 ), color and chlorophylls and carotenoids content. A differential pulse voltammeter was also used to monitor the changes in a-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 firsts 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 a-tocopherol contents which clearly decreased as long as the exposure time increases. After 15 min of heating the electrochemical signal, due to the a-tocopherol, disappear completely in the voltamogram.

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a b s t r a c tThe present work evaluates the potential of hazelnut kernels as a source of antioxidants to be incorporated into new products. First, the effects of extraction conditions on the isolation of hazelnut kernels' total phenols and antioxidants were evaluated. Six conditions, involving different solvents (water, methanol and aqueous acetone) and contact times, were studied. The highest total phenol contents were obtained with boiling water for 30 min, 44.3 ± 7.7 mg GAE/g extract , and 80% (v/v) aqueous acetone solution for 24 h, 36.2 ± 8.8 mg GAE/g extract . Increasing the contact time for the acetonic extractions did not improve the total phenols content. Regarding antioxidant activity, the highest DPPH-scavenging effect value was obtained with 80% (v/v) aqueous acetone for 24 h with an effective concentration (EC 50 ) equal to 1.12 ± 0.07 mg/mL. When other nuts -walnuts, almonds, pine nuts and peanuts -were extracted under this condition, only walnut extract exhibited higher phenol content (268 ± 32 mg GAE/g extract ), antioxidant activity as measured by reducing power (EC 50 = 0.091 ± 0.015 mg/mL) and free radical scavenging capacity (DPPH assay) (EC 50 = 0.060 ± 0.010 mg/mL) than hazelnut extract. The present work demonstrates that some nuts might be a natural source of bioactive compounds that can be incorporated into new health-related products or be substitutes of synthetic compounds of questionable safety, promoting human health and reducing disease risks.

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