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 (mu g GAE / 5 mg essential oil), respectively. To compare with the standard reference BHA (mu g/mL), their EC50 were in the order: BHA (25.11 mu g/mL) < cinnamon bark (90.63 mu g/mL) <origanum (751.51 mu g/mL). The photochemiluminescence assay was also employed to investigate the antioxidative capabilities of lipid-soluble substances (ACL). The results were as follow: cinnamon bark (133.9 +/- 0.26 mu mol trolox/g) > origanum (62.63 +/- 1.73 mu mol trolox/g) > theme wild (5.88 +/- 0.16 mu mol 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.
