Antioxidant capacity of walnut (Juglans regia L.): contribution of oil and defatted matter
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Several studies have concluded that walnut exhibits greater antioxidant capacity than any other nuts. However, the contribution to antioxidant capacity of the two major fractions of walnut (defatted matter and oil) is unknown, and the aim of the present work is to elucidate it. Antioxidant capacity was evaluated in walnut oil, defatted matter, and whole walnut. The results showed that the defatted matter provided the bulk of the antioxidant capacity (estimated about 332 μmol Trolox/g dm) of this nut, a major proportion derived from insoluble tannins. The contribution of walnut oil to the overall antioxidant capacity of walnut (FRAP and ABTS assays) is less than a 5%. It was observed that oil interfered in the determination of antioxidant capacity of whole walnut, a fact that could affect the data reported in the literature. Separate determination of oil and defatted mater antioxidant capacity is recommended.
KeywordsDefatted matter Antioxidants Walnut Oil Juglans regia L.
Cupric reducing/antioxidant capacity
Ferric reducing/antioxidant power
Oxygen radical absorbance capacity
Thiobarbituric acid reactive substances
Total peroxyl radical trapping antioxidant activity
The present research was performed under the financial support of the Spanish Ministry of Education and Science (project AGL 2004-07579-C04-01/ALI). J. Pérez-Jiménez thanks the Consejo Superior de Investigaciones Científicas for granting her an I3P scholarship, financed by the European Social Fund. S. Arranz thanks the Ministerio de Educación y Ciencia for granting her an FPI scholarship.
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