Radical scavenging activity of volatile oils of herbs traditionally used to spice cooking butter in Ethiopia

Abstract

Since time immemorial food preservation has been a common practice. Most of these preservatives come form natural sources such as herbs and spices. Currently, synthetic antioxidants are extensively incorporated in foods and cosmetics for the prevention of lipid peroxidation. Some of these synthetic antioxidants, however, have been shown to be carcinogenic and since quite recently, efforts are underway to develop effective and safer natural antioxidants targeting mainly herbs and spices. In Ethiopia, the aerial parts of Lippia adoensis var. koseret and Ocimum basilicum var. purpurascens, rhizomes of Zingiber officinalis, and seeds of Aframomum corrorima are used to spice cooking butter and also to preserve its freshness for a long time. The volatile oils of these plants, obtained by hydrodistillation, and the methanolic extract of spiced butter were tested for their radical scavenging activity using TLC and 2,2- diphenyl-1-picrylhydrazyl (DPPH) assay. The antioxidant principles of the examined volatile oils were detected in the methanolic extract of the cooking butter spiced with the four plants. Quantitative studies showed that the volatile oils were able to reduce the stable radical, DPPH to the yellow coloured 2,2-diphenylpicrayl-1-hydrazine in a dosedependent manner. The strongest effect was exhibited by the essential oil of the aerial parts of O. basilicum var. purpurascens (IC₅₀ = 0.04 µl/ml) whereas the weakest effect was shown by that of the seeds A. corrorima (IC₅₀ = 34.9 µl/ml). The antioxidant potentials of the oil obtained from the aerial parts of L. adoensis var. koseret and the rhizomes of Z. officinalis were somewhat intermediate (IC₅₀ = 6.13 and 9.66 µl/ml, respectively). The results of this study may provide a rational explanation for the traditional use of these plants to prevent rancidity and preserve the freshness of cooking butter, which could be attributed to their radical scavenging activity.

Keywords: spiced butter, volatile oils, TLC analysis, antioxidant activity, DPPH assay

Ethiopian Pharmaceutical Journal Vol. 23 2005: 7-14