Ultrasound-Assisted Delivery of Natural Antioxidants Enhances the Oxidative Stability of Hempseed Oil

Background: Hempseed oil is highly valued nutritionally for its rich content of polyunsaturated fatty acids, but this same composition renders it highly susceptible to lipid oxidation, a process further accelerated by chlorophyll-mediated photo-oxidation. Natural phenolic antioxidants such as quercetin and ferulic acid offer a potential solution given their potent radical-scavenging activity, yet their limited oil solubility constrains practical application. Ultrasound-assisted incorporation may overcome this barrier by improving antioxidant dispersion and, consequently, leading to a better inhibition of lipid oxidation. Aims: This study aimed to optimize the incorporation of quercetin and ferulic acid into hempseed oil using ultrasound treatment and to investigate their individual and combined antioxidant effects on improving the oil's oxidative stability. Methods: The antioxidant capacities of quercetin and ferulic acid were assessed via DPPH and ABTS radical-scavenging assays. Ultrasound-assisted incorporation into hempseed oil was optimized by varying sonication amplitude and duration, with oxidative stability evaluated by the Rancimat method. The effects of antioxidant concentration and combination were then examined, and response surface methodology based on a central composite design was applied to optimize the formulation of antioxidants. Results: Quercetin showed the strongest radical-scavenging activity, followed by ferulic acid, with both natural antioxidants yielding substantially lower IC₅₀ values than the synthetic antioxidant BHT in both assays. Sonication at 20% amplitude for 5 min effectively dispersed the antioxidants without compromising the oil's oxidative stability. Both compounds increased the induction period of hempseed oil in a concentration-dependent manner, though quercetin achieved equivalent protection at 200 ppm to that requiring roughly tenfold higher concentrations of ferulic acid. Response surface methodology yielded a highly significant predictive model (R² = 0.995; p < 0.0001), confirming significant individual contributions of both antioxidants and enabling optimization of their combined formulation. Conclusions: Ultrasound-assisted incorporation of quercetin and ferulic acid is an effective strategy for enhancing the oxidative stability of hempseed oil. The optimized process offers a promising natural alternative to synthetic antioxidants for stabilizing polyunsaturated edible oils, supporting the development of clean-label, lipid-based food products.