The Antioxidant Effectiveness of Thyme Oil, α-Tocopherol and Ascorbyl Palmitate on Evening Primrose Oil Oxidation

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Abstract
Three antioxidants thyme oil, α-tocopherol and ascorbyl palmitate at final concentrations 250, 500, 750 and 1000 ppm, were assessed for their antioxidant effectiveness, at retarding autoxidation of evening primrose oil at 50°C for one week as measured by peroxide formation and decomposition. With respect to peroxide formation, all three antioxidants provided significant protection as compared with the control, α-tocopherol exhibiting the greatest protection between 250-750 ppm, followed by thyme oil and ascorbyl palmitate, although at 1000 ppm, thyme oil exhibited highest inhibition. Decomposition of peroxides into aldehydes was significantly reduced in the presence of all three antioxidants at all concentrations. At 250 ppm both thyme oil and α-tocopherol were significantly more effective than ascorbyl palmitate. However, there were no significant differences between the antioxidants at the remaining concentrations. In contrast with peroxide formation, the ability of thyme oil, α-tocopherol and ascorbyl palmitate at inhibiting peroxide decomposition decreased with increasing concentration.