Tocopherols and Phytosterols: Degradation and Antioxidant Regulation in Walnut Oil During Storage

The variations in tocopherols and phytosterols during the oxidation of walnut oils (Wen-185, Xiangling, and Dama oils) were analyzed, and their antioxidant effects were compared. Under both ambient temperature and accelerated oxidation conditions, the degradation order of tocopherols in walnut oils was α-tocopherol > γ-tocopherol > δ-tocopherol. Phytosterols exhibited less degradation than tocopherols under both oxidation conditions, and tocopherols were more strongly associated with oil oxidation than phytosterols. When δ-tocopherol degradation reached 15%–20%, the peroxide value approached 20 meq/kg, highlighting its potential as an indicator of oil oxidation. Further studies on the antioxidant effectiveness of tocopherols revealed that the optimal effect was achieved as 400 mg/kg α-tocopherol was added at Day 16 under ambient temperature. These findings suggested that δ-tocopherol can serve as an indicator of walnut oil oxidation, and appropriately timed and dosed α-tocopherol supplementation can significantly delay oxidation in walnut oils.

Practical Applications: This study compared the changes and degradation of tocopherols and phytosterols in different walnut oils. The results suggested that tocopherol degraded faster than phytosterol, with a closer correlation to oil oxidation, and α-tocopherol underwent degradation preferentially. Furthermore, the antioxidant effectiveness of tocopherols was analyzed. The results showed that proper quantity and timing of α-tocopherol addition can enhance antioxidant effect, and δ-tocopherol can assess the oxidation of walnut oils as an concomitant indicator. This study has expanded the application of endogenous concomitants in the antioxidant properties of walnut oils. It has laid a theoretical foundation for the antioxidant properties of walnut oils.