Prolonging oxidation stability of peony (Paeonia suffruticosa Andr.) seed oil by endogenous lipid concomitants: Phospholipids enhance antioxidant capacity by improving the function of tocopherol

Abstract

Peony (Paeonia suffruticosa Andr.) seed oil (PSO) is susceptible to oxidation owing to its richness in unsaturated fatty acids, which limits its widespread use. In the present work, two typical endogenous lipid concomitants (tocopherols and phospholipids) in PSO were employed as antioxidants to improve the oxidative stability of PSO. As a first step, we used the Rancimat method to investigate the interaction between tocopherols (T) and phospholipids (P) as antioxidants. A study showed that adding T extended the oxidation induction period of PSO to 2.48 ± 0.03 h, while P had almost no antioxidant activity. The combination of T and P exhibited synergistic effects, and the oxidation induction period of PSO increased to 3.00 ± 0.01 h, significantly improving PSO's oxidative stability. Then, by comparing the oxidative depletion of lipid concomitants during accelerated oxidation of PSO samples, when both T and P were present, T was slowly degraded over 90 min, while the content of T increased at 120 min. Combined with the results of electron spin resonance (ESR) spectroscopy, a proposed mechanism of synergistic effects between T and P is that phosphatidylethanolamine (PE) could provide protons to tocopherol free radical, thus achieving the regeneration of the antioxidant capacity of T. However, phosphatidylcholine (PC) and phosphatidylinositol (PI) are almost ineffective. The quenching mechanism of T by PE is static, and van der Waals forces and hydrogen bonding interactions drive the interaction between PE and T. The findings of this study were confirmed by fluorescence spectroscopy and calculations based on quantum chemistry. This research helps improve PSO's antioxidant capacity, provides recommendations for moderate retention of lipid concomitants during oil processing, and increases the potential of PSO for applications in the cosmetic, pharmaceutical, and food industries.