Antioxidant activities of Rosmarinus officinalis L. essential oil obtained by hydro-distillation and solvent free microwave extraction

Abstract

The essential oils of Rosmarinus officinalis L. growing in a rural area within the Nkonkobe Municipality of the Eastern Cape, South Africa, were extracted using the solvent free microwave extractor (SFME) and hydro-distillation (HD) methods. The antioxidant and free radical scavenging activity of the obtained oils were tested by means of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH⁺) assay and β- carotene bleaching test. In the DPPH⁺ assay, while the free radical scavenging activity of the oil obtained by SFME method showed percentage inhibitions of 48.80, 61.60 and 67.00%, the HD oil showed inhibitions of 52.20, 55.00 and 65.30% at 0.33, 0.5 and 1.00 mg/ml, respectively. In the β- carotene bleaching assay, the percentage inhibition increased with increasing concentration of both oils, with a high antioxidant activity of the oil obtained through the SFME than through the HD method. The significance of this observation is discussed with respect to the properties of essential oils obtained using different methods.

Key words: Essential oil, antioxidant, hydrodistillation, solvent free microwave extraction; Rosmarinus officinalis.