Antioxidant Activity Displayed by Phenolic Compounds Obtained from Walnut Oil Cake used for Walnut Oil Preservation

The objective of this work was to evaluate the performance of various antioxidants (ethyl acetate-soluble polyphenols: PAE; water-soluble polyphenols: PH; and butylated hydroxytoluene [BHT]) on the preservation of walnut oil (W) during storage. An oven test was conducted on the walnut oil samples: without antioxidants (control: WC) and with antioxidants: PAE (WPAE), PH (WPH), and BHT (WBHT) during a 16-day storage at 60 degrees C temperature. Chemical parameters related to deterioration were analyzed during storage: peroxide value (PV), conjugated dienes (CD) and conjugated trienes (CT), and carotenoid content (CC). Volatile compounds were also analyzed. PV, CD, CT, and volatile compounds related to oxidation of lipids such as; nonanal, hexanal, butanal, and (E)-2-heptenal increased in all samples during storage. The increase of these variables was greater in WC and lower in WPAE and WPH. WPAE, WPH, and WBHT displayed a better preservation of volatile compounds that influence the walnut-characteristic flavor like D-limonene, and a lower increase of aldehydes and furans. The CC exhibited a decrease in all samples during storage. WPAE presented the greatest CC value along the storage and was followed by WPH. Antioxidants helped to preserve walnut oil against deterioration processes. PAE and PH displayed good antioxidant activity and in some cases showed a better performance for quality preservation of walnut oil compared to the BHT antioxidant.