DPPH free-radical scavenging activity, total phenolic contents and chemical composition analysis of forty-two kinds of essential oils

Forty-two commonly used essential oils were investigated for the antioxidant capabilities by DPPH free-radical scavenging activity, total phenolic contents and photochemiluminescence (PCL) assay. At the concentration of 5 mg/mL, cinnamon bark (91.4 ± 0.002%), origanum (86.66 ± 0.008%) and thyme wild (52.54 ± 0.016%) were shown to own the strongest DPPH free-radical scavenging activity. Their total phenolic contents were 658.40 ± 4.383, 1107.20 ± 0.768 and 275.50 ± 0.607 (μg GAE / 5 mg essential oil), respectively. To compare with the standard reference BHA (μg/mL), their EC50 were in the order: BHA (25.11 μg/mL) < cinnamon bark (90.63 μg/mL) origanum (62.63 ± 1.73 μmol trolox/g) > theme wild (5.88 ± 0.16 μmol trolox/g). The chemical compositions of cinnamon bark, origanum and thyme wild were analyzed by GC-MS and followed by DPPH free-radical scavenging activity assay to confirm that eugenol, carvacrol and thymol were the major compositions contributing the antioxidative capabilities of the essential oils.