Improving Oxidative Stability of Virgin Olive Oil: Comparison of Zataria Multiflora Essential Oil with α-Tocopherol

Virgin olive oil is a vastly consumed product, with widespread appreciation for its good nutritional and health properties. However, oxidation can reduce its quality. The aim of this study was to investigate how the essential oil of Zataria multiflora (Shirazi thyme) can contribute to the prevention of virgin olive oil oxidation in comparison with the actions of α-tocopherol and BHT. Furthermore, the synergistic activities of citric acid with BHT, Z. multiflora essential oil, and α-tocopherol were investigated.
Antioxidant activity of the essential oil was determined using radical scavenging capacity and reducing power assays. Virgin olive oil samples were stored at 60±1 °C in closed amber bottles for 16 days. Oxidation levels of samples were determined by measuring peroxide, anisidine, TOTOX, K232, K268 values, and chlorophyll and carotenoid contents of the samples during the storage period.
Z. multiflora essential oil exhibited a significant radical scavenging capacity and reducing power. Peroxide, anisidine, TOTOX, K232, and K268 values of samples containing Z. multiflora essential oil were significantly lower than those of the control group (without antioxidants). Z. multiflora essential oil reduced the oxidation of virgin olive oil to the same extent as BHT did. Z. multiflora essential oil was more effective than α-tocopherol. The synergistic activities between citric acid and the various compounds, i.e. BHT, Z. multiflora essential oil, and α-tocopherol were 2.42%, 4.74%, 1.28% respectively.
In general, Z. multiflora essential oil can be considered as natural antioxidant for the stabilization of virgin olive oil against oxidation.