NASA Human Research Program Investigators' Workshop (2012) 4242.pdf Comprehensive Assessment of Antioxidant Activity of Essential Oils Kevin Anthony, Fawzia Abdel Rahaman, Suziat A. Deolu-Sobogun, S.A and Mahmoud A. Saleh Department of Chemistry, Texas Southern University, Houston, Texas ABSTRACT Essential oils have been studied for their unique ability to act as antioxidants. Antioxidant activities of 445 essential oils of 47 different botanical families were evaluated for their antioxidant activities as free radical scavenging agents using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. 84 oils showed 50% or more inhibition at a concentration of 1.25 mg/mL. The 84 most active oil samples were further evaluated for their scavenging activities using series of dilutions to estimate their IC50. The IC50 of the 84 most active oils ranged from 4 to 1000 ppm (μg/mL). Oils having an IC50 of 300 ppm or less (20 samples) were selected for more detailed analysis including thin layer chromatography (TLC), gas chromatography/mass spectrometry (GC/MS), high performance liquid chromatography HPLC and bioautography. Essential oils of the botanical family Myrtaceae were the most effective antioxidant and they were found to be rich in carvacrol, eugenol and thymol.