Antioxidant/lipoxygenase inhibitory activities and chemical compositions of selected essential oils

Twenty-five essential oils were tested for antioxidant activities using a conjugated diene assay, the aldehyde/carboxylic acid assay, the DPPH free radical scavenging assay, and the malonaldehyde/gas chromatography (MA/GC) assay. They were also tested for lipoxygenase inhibitory activities using the lipoxygenase inhibitor-screening assay. Thyme oil exhibited the greatest antioxidant effect in all assays (80-100%) except in the DPPH assay (60%). Clove leaf oil showed activities comparable to those of thyme oil (53-100%). Cinnamon leaf oil showed strong activities in the aldehyde/carboxylic acid assay (100%) and DPPH assay (84%), but only moderate activities in the conjugated diene assay (24%) and MA/GC assay (48%). Basil oil exhibited a strong effect in the DPPH assay (86%) and moderate activities in the MA/GC assay (35%). Bergamot oil exhibited 100% antioxidant activity in the aldehyde/carboxylic acid assay. Eucalyptus and chamomile oils showed appreciable activities only in the conjugated diene assay. Bitter orange oil exhibited moderate antioxidant activity (53%) only in the MA/GC assay. Aloe vera oil exhibited the greatest lipoxygenase inhibitory activity (96%), followed by thyme oil (86%) and bergamot oil (85%) at a concentration of 0.5 microg/mL. Chamomile oil showed slight lipoxygenase inhibitory activity at 0.5 microg/mL but strong lipoxygenase inducing activity at 5 microg/mL (-123%). Thyme and clove leaf oils contained high levels of thymol (23%) and eugenol (77%), respectively, as a principal of the antioxidant activity. The results obtained in the present study suggest that some essential oils possess strong medicinal activities, which can be utilized for treatment of certain diseases.