Preparation and Characterization of Quercetin Phospholipid Complex and Its Effect on the Oxidative Stability of Walnut Oil

To expand the application of quercetin, quercetin phospholipid complexes were optimally prepared by the solvent method. The complexes were structurally characterized and evaluated for their antioxidant capacity in vitro, and the effect of the complexes on the oxidative stability of walnut oil was further investigated. The optimal process conditions were as follows: the solvent was anhydrous ethanol, the mass ratio of quercetin to phospholipid was 1:3, the concentration of quercetin was 0.5 mg/mL, and the reaction was stirred at 50 ℃ for 4 h, with an average compounding rate of 99.49%. Moreover, this condition can effectively prepare new quercetin phospholipid complexes that differ from quercetin or phospholipids. The complexes were formed by hydrogen bonding of the hydroxyl group of quercetin to the polar end of phospholipid, and the solubility of the complexes in water and n-octanol was better than that of the quercetin and the physical mixtures of quercetin and phospholipids. The in vitro antioxidant capacity of the quercetin phospholipid complex did not differ significantly from that of free quercetin at the same mass concentration. Walnut oil was stored at 60 ℃ for 18 d. The results showed that the quercetin phospholipid complexes more effectively slowed down the increase of acid value, peroxide value, conjugated diene value (CD), and conjugated triene value (CT) of walnut oil, and the antioxidant effect was significantly better than that of quercetin (P<0.05). Moreover, the acid value of walnut oil was significantly and positively correlated with the peroxide value, CD value, and CT value. The quercetin phospholipid complexes can significantly improve the antioxidant stability and prolong the shelf life of walnut oil without affecting the sensory quality, which has good development and utilization value.