Effects of natural phenolics and synthetic antioxidants on the oxidative thermal stability of refined and purified sunflower oils

The antioxidant activity of phenolic compounds [thymol (T), carvacrol (C), and thymoquinone (TQ)] was compared with commercial antioxidants [butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and alpha-tocopherol] using the beta-carotene bleaching and ABTS assays. At 1000 ppm concentration, commercial antioxidants showed better antioxidative properties (94.9-95.9%) than phenolic compounds (64.9-85.7%) according to beta-carotene bleaching assay. In the ABTS assay, except for BHT, BHA and alpha-tocopherol exhibited stronger radical scavenging activity than phenolic compounds. Regarding the Rancimat method, BHT-enriched stripped sunflower oil (SSO) had the longest induction period. At the same time, phenolic compounds caused a slightly higher increase in the induction periods than the control sample. Refined sunflower oil (RSO) enriched with BHT at 100 ppm was the most stabile during storage at 60 degrees C. Phenolic compounds added to RSO at 250, and 500 ppm exhibited less protection to lipid oxidation than BHT, while phenolic compounds, notably TQ, improved the RSO's oxidative stability. BHT at 100 ppm showed a strong antioxidant effect on SSO during storage at 60 degrees C. The effect of phenolic compounds, especially TQ on SSO, were lower than BHT, but higher than the control sample at 60 degrees C. The results are essential to applying new natural compounds as antioxidant agents in oils, fats, and lipids-rich foodstuffs.