THYMUS CAPITATUS GROWN IN TUNISIA: ANTIOXIDANT ABILITY OF THE ESSENTIAL OILS ON LINOLEIC ACID EVALUATED BY DIFFERENT METHODS

The essential oils of Tunisian thyme (Thymus capitatus Hoff. et Link.) were isolated by hydrodistillation from the dried aerial parts of plants collected from both flowering and vegetative stages. The chemical composition of the oils was analysed by GC and GC/MS. Carvacrol was the dominant component in oils from both the flowering (68%) and vegetative (73%) stages. Antioxidant activity measurements were done at 10 different occasions during a 72-day incubation period using 3 different methods: peroxide value, p-anisidine method, and A₂₃₂/A₂₇₀ (absorbance at 232 nm/absorbance at 270 nm). Controls were prepared under the same conditions, but without any antioxidant. The capacity of T. capitatus oils to prevent the peroxidation of C18:2 was similar to that of butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) throughout the entire incubation period. The p-anisidine method showed that BHA seems to promote a 2,4-decadienal formation as sample values were higher than those observed for the control. The remaining samples did not show any major differences when compared with the control. The A₂₃₂/A₂₇₀ absorbance measurements produced a higher ratio in the control than the ratios in the essential oil, BHA and BHT samples, respectively, indicating the a significantly less conjugated diene formation in the samples compared with the control.