Comparison of Antioxidant and Free Radical Scavenging Activities of the Essential Oils from Flowers and Fruits of Otostegia persica Boiss

The aerial parts of the endemic plant of Otostegia persica Boiss. in two different stages of flowering and fruiting were hydro-distilled to extract oils in the yields of 0.3 and 0.15% (v/w), respectively. The oils were analyzed by GC and GC/MS. Twenty-eight and thirty-one components were identified, representing 97.59 and 94.61% of the oils, respectively. The main compounds of the essential oil flowers (EOFL) were alpha-pinene (17.21%), 1-octen,3-ol (13.44%) and cubenol (7.27%), whereas diisooctyl phthalate (45%) and hexadecanoic acid (11.07%) were the major constituents of the essential oil of the fruits (EOFR). The oils were screened for their possible antioxidant activities by two complementary test systems, namely DPPH free radical-scavenging and ammonium thiocyanate. In both tested systems, EOFL exerted greater antioxidant and radical scavenging activity. In the first case, EOFL exerted antioxidant activity with an IC₅₀ 19.8±1.8 μg mL^-1 almost similar to BHA and ascorbic acid (15.2±1.1 and 17.4±1.3), respectively. In the ammonium thiocyanate system, the inhibition rate of oxidation of linoleic acid for EOFL was estimated 93.5±2.8. The higher activity of this oil in comparison to EOFR may be attributed to its high content of monoterpenes, especially oxygenated ones in the oil of the flowers.