Free-radical scavenging activity of 15 essential oils obtained by hydro-distillation from 12 species (8 families) of Thai herbs was studied using DPPH assay. It was found that 6 types of essential oils from nutmeg tree seeds (or nutmeg) and arils (or mace), fruits, and leaves (Myristica fragrans Houtt.),‹ holy basil leaves (Ocimum sanctum L.), cajuput tree leaves (Melaleuca cajuputii Powell) and fishwort fruits (Houttuynia cordata Thunb.) were potent free-radical scavenger with IC₅₀ at 0.60, 0.79, 2.39, 2.88, 3.24 and 4.19 μl/ml, respectively. Compared to a positive control, vitamin C showed IC₅₀ at 3.55 μg/ml. The physico-chemical properties of these oils were also studied using identification (color test, thin-layer chromatography, gas chromatography-mass spectrometry), miscibility in ethanol, relative density, and refractive index.

KEY WORDS:  free-radical scavenging activity,  DPPH assay,

essential oils,  physicochemical properties