Studies on the antioxidant activity of the essential oil and methanol extract of Marrubium globosum subsp. globosum (lamiaceae) by three different chemical assays

This study is designed to examine the chemical composition and in vitro antioxidant activity of the essential oil and sub-fractions of the methanol extract of Marrubium globosum subsp. globosum. The GC and GC–MS analysis of the essential oil were resulted in the determination of 84 components representing 88.2% of the oil. The major constituents of the oil were spathulenol (15.8%), β-caryophyllene (9.0%), caryophyllene oxide (7.9%), germacrene D (6.5%), and bicyclogermacrene (3.1%). Antioxidant activities of the samples were determined by three different test systems namely DPPH, β-carotene/linoleic acid and reducing power assay. In DPPH system, the weakest radical scavenging activity was exhibited by the essential oil (1203.38 ± 7.18 μg ml−1). Antioxidant activity of the polar sub-fraction of methanol extract was superior to the all samples tested with an EC50 value of 157.26 ± 1.12 μg ml−1. In the second case, the inhibition capacity (%) of the polar sub-fraction of methanol extract (97.39% ± 0.84) was found the strongest one, which is almost equal to the inhibition capacity of positive control BHT (97.44% ± 0.74). In the case of reducing power assay, a similar activity pattern was observed as given in the first two systems. Polar sub-fraction was the strongest radical reducer when compared with the non-polar one, with an EC50 value of 625.63 ± 1.02 μg ml−1. The amount of the total phenolics was highest in polar sub-fraction (25.60 ± 0.74 μg/mg). A positive correlation was observed between the antioxidant activity potential and total phenolic level of the extracts. On the other hand, total flavonoid content was found equal for the both sub-fractions.