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.

[1]  Kristina Andersson,et al.  Influence of oxygen and copper concentration on lipid oxidation in rapeseed oil , 1998 .

[2]  M. C. Pérez-Camino,et al.  Microwave and Conventional Heating Effects on Some Physical and Chemical Parameters of Edible Fats , 1997 .

[3]  L. Cossignani,et al.  Changes in olive oil composition due to microwave heating , 1998 .

[4]  Beatriz P. P. Oliveira,et al.  Chemometric characterization of three varietal olive oils (Cvs. Cobrançosa, Madural and Verdeal Transmontana) extracted from olives with different maturation indices , 2007 .

[5]  D. Ahn,et al.  Antioxidant activities of six natural phenolics against lipid oxidation induced by Fe2+ or ultraviolet light , 1998 .

[6]  P. Baptista,et al.  Antioxidant activity of Agaricus sp. mushrooms by chemical, biochemical and electrochemical assays , 2008 .

[7]  J. Pereira,et al.  Effect of olive fruit fly infestation on the quality of olive oil from cultivars cobrançosa, madural and verdeal transmontana , 2004 .

[8]  J. German,et al.  Comparison of natural polyphenol antioxidants from extra virgin olive oil with synthetic antioxidants in tuna lipids during thermal oxidation. , 1999, Journal of agricultural and food chemistry.

[9]  H. Yoshida,et al.  Microwave Energy Effects on Quality of Some Seed Oils , 1990 .

[10]  T. Gomes,et al.  Changes in the fatty acid composition of vegetable oils in model doughs submitted to conventional or microwave heating , 2003 .

[11]  M. Motilva,et al.  Pigment profile and colour of monovarietal virgin olive oils from Arbequina cultivar obtained during two consecutive crop seasons. , 2008, Food chemistry.

[12]  H. Yoshida,et al.  Effects of microwave energy on the relative stability of vitamin E in animal fats , 1992 .

[13]  K. Murakami,et al.  ANTIOXIDANT EFFECT OF DIPICOLINIC ACID ON THE METAL-CATALYZED LIPID PEROXIDATION AND ENZYME INACTIVATION , 1998 .

[14]  M. Hassanein,et al.  Changes occurring in vegetable oils composition due to microwave heating , 2003 .

[15]  A. S. Csallany,et al.  Chlorophyll and β-carotene pigments in moroccan virgin olive oils measured by high-performance liquid chromatography , 1991 .

[16]  Alberto Escarpa,et al.  electrochemical index as a screening method to determine total polyphenolics in foods : A proposal , 2005 .

[17]  J. Pereira,et al.  Influence of olive storage period on oil quality of three Portuguese cultivars of Olea europea, Cobrançosa, Madural, and Verdeal Transmontana. , 2002, Journal of agricultural and food chemistry.

[18]  B. Gandul-Rojas,et al.  Color-pigment correlation in virgin olive oil , 1991 .

[19]  M. C. Pérez-Camino,et al.  MICROWAVE AND CONVENTIONAL HEATING EFFECTS ON THERMOXIDATIVE DEGRADATION OF EDIBLE FATS , 1997 .

[20]  Christian Gertz,et al.  TESTING AND COMPARING OXIDATIVE STABILITY OF VEGETABLE OILS AND FATS AT FRYING TEMPERATURE , 2000 .

[21]  Joana S. Amaral,et al.  Classification of PDO olive oils on the basis of their sterol composition by multivariate analysis , 2005 .

[22]  W. Artz,et al.  Effects of relative humidity on lipid autoxidation in a model system , 1988, Lipids.

[23]  Yrjö H. Roos,et al.  Oxidation of methyl linoleate encapsulated in amorphous lactose-based food model , 1991 .