Antioxidant activity and total phenolic compound content of certain medicinal plants

Aqueous extracts were prepared from eight medicinal plants and other plants were prepared as essential oils. The radical-scavenging ability of each plant extract was determined by the 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging assay. The total phenolic content of plants was determined by the Folin–Ciocalteu reagent in terms of gallic acid equivalents. The DPPH scavenging potential of the aqueous extracts ranged from 17 to 79%, whereas the essential oils showed inhibition of the DPPH activity in the 12–88% range. The highest inhibition of DPPH radicals was observed for Pinus halepensis extract. Meanwhile, amongst the essential oils, the greatest antioxidant potential was exhibited by Nigella sativa. The Bauhinia variegate extract had the highest phenolic content (149.18 mg/g gallic acid equivalents), followed by Albizzia lebbeck (148.00 mg/g) and Pinus halepensis (145.67 mg/g), whereas, amongst the essential oils, the highest phenolic content (98.57 mg/g) was found for Thymus vulgaris. The lowest contents were observed for Kigelia africana and Rosmarinus officinalis. The antioxidant activity had a positive correlation (R=0.654) with the phenolic content of most aqueous extracts, whereas it had a weak correlation using the essential oils (R=0.335). This confirms that the phenolic content of aqueous extracts may contribute towards their antioxidant properties.