Antioxidant activity of the essential oils of Thymbra capitata, Origanum vulgare, Thymus mastichina, and Calamintha baetica

Some aromatic plants such as Thymbra capitata, Origanum vulgare and Calamintha baetica are used in some Portuguese traditional meat dishes, particularly in rabbit meat, tomato salads, fish food, escargot and olives. In the present work, the antioxidant ability of the essential oils extracted from T capitata, O. vulgare, C. baetica and Th. mastichina cultivated in a field of the Regional Direction of Agriculture of Algarve (Portugal) was studied. The oils, extracted by hydrodistillation, were analysed by gas chromatography and gas-chromatography coupled to mass spectrometry. The antioxidant activity was determined using a modified thiobarbituric acid-reactive substances (TBARS) method, measuring the scavenging effect on 1,1-diphenyl-2picrylhydrazyl (DPPH) radical method, determining the reducing power method, and monitoring the chelating effect on ferrous ions method. The results showed that the oils from O. vulgare and T capitata had practically the same capacity of preventing the lipid oxidation of those of BHT and BHA. T capitata oil was the most effective for the scavenging effect on DPPH as any capacity for this effect was practically absent in the oils of Th. mastichina and C. baetica. These results can be explained by the relative high concentrations of phenol compounds in those plants. The essential oil isolated from C baetica possessed the best ability of chelating ferrous ions, something practically inexistent in the remaining other plant samples and the BHT and BHA. The reducing power of the essential oils was much lower than those observed for the synthetic antioxidants, nevertheless among the oils, those from O. vulgare and T capitata were the most effective. The chelating effect of the C baetica oil can be used as a synergistic antioxidant, that is, this oil can be used together with a phenolic antioxidant in the food product, but at lower levels.