Prooxidant Effect Of Polyphenols On The Oxidative Stability Of Almonds And Walnuts After Thermal Treatments

CECILIA L. SALCEDO; MÓNICA A. NAZARENO

Sitges, Barcelona

Conferencia; 5th International Conference on Polyphenols and Health; 2011

Universidad de Barcelona

PROOXIDANT EFFECT OF POLYPHENOLS OF ALMONDS AND WALNUTS BROWN SKINS AFTER HEATING Introduction Walnuts and almonds are nutritionally valuable foods, mainly due to their high lipid and antioxidant compounds contents. Lipids are constituted in their majority by unsaturated fatty acids, which are readily prone to oxidation reactions and become then unstable. Both nuts are also rich in phenolic compounds, which are concentrated in their brown skins, and they have demonstrated their antioxidant ability. In order to determine the possible effects of brown skin phenolic compounds on the oxidative status of ground walnuts and almonds, primary and secondary oxidation products formation after short term thermal treatments (30 min) were analysed. Materials and Methods Primary oxidation products were analysed by hydroperoxides formation, using linoleic acid as oxidisable substrate in a reverse micellar system formed by AOT/isooctane. Phenolic compounds aqueous extracts were put into the micelle, in order to mimic the nut biological environment. On the other hand, secondary oxidation products of peeled and unpeeled nuts were analysed by TBARS method. Both techniques were carried out at different temperatures. Results At 70 and 100°C, when aliquots of phenolic compounds extracts were added to the micellar systems, hydroperoxides levels were higher than those without phenolic compounds extracts. At room temperature, unpeeled nuts showed higher MDA equivalents than peeled ones, demonstrating a brown skin antioxidant effect, but, on the contrary, at 70°C and 100°C unpeeled nuts showed significantly higher MDA equivalents than peeled ones. Conclusion High levels of both primary and secondary oxidation product compounds in presence of brown skins, indicate that they exert a prooxidant effect when samples are heated at temperatures of 70°C or higher. Secondary oxidation product contents were higher in walnuts than in almonds, which is consistent with the walnut oil fraction richer in oxidisable fatty acids than the almond one.