Phytochemical and antioxidant properties of different solvent extracts of Kirkia wilmsii tubers

ABSTRACT

Objective To determine suitable phytochemical extraction solvents, screen for phytochemicals, determine the total phenol and flavonoid contents and the antioxidant activities of different solvent extracts of Kirkia wilmsii (K. wilmsii), an ethnomedicine in South Africa. Methods Extractions were performed from dried tubers of the K. wilmsii plant, using several solvents and varying extraction times. Extract yields were determined and suitable extraction solvents were selected. Total phenol and flavonoid contents of the extracts were determined spectrophotometrically using gallic acid and quercetin as standards. The free radical scavenging activity of the extracts was investigated using 1,1-diphenyl-2-picrylhydrazyl radical. Results Phytochemical screening confirmed the presence of phenolics, flavonoids, terpenoids, tannins, cardenolide deoxy sugars and reducing sugars. Of the 12 solvent extracts used, six gave yields higher than 5%, while the other six gave yields less than 1%. The highest extract yield of 52.9% was obtained using 80% methanol while the lowest yield of 7.3% was obtained using ethanol at 60 min. The 80% methanol, methanol/chloroform/water (1253) and 60% methanol extracts were significantly higher than those of ethanol, methanol and water (P < 0.05). Total phenolic content recorded extracts ranged from (45.32 ± 0.50) to (122.84 ± 0.31) mg gallic acid equivalent per gram. A maximum total flavonoid content of (917.02 ± 0.10) mg quercetin equivalent per gram and a minimum of (206.26 ± 0.10) mg quercetin equivalent per gram were recorded for methanol and water, respectively. The flavonoid content for methanol was significantly higher than all the other extracts (P < 0.05). The scavenging profiles of K. wilmsii extracts were significantly lower (P < 0.05) than that of ascorbic acid and IC