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

Abstract

ObjectiveTo 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. MethodsExtractions 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. ResultsPhytochemical 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 (12:5:3) 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 IC50 values ranged from 129.94 μg/mL for methanol to 225.04 μg/mL for water. An IC50 value of 56.52 μg/mL was obtained with ascorbic acid. ConclusionsEthanol, methanol, methanol/chloroform/water, 80% methanol, 60% methanol and water can be used as suitable phytochemical extraction solvents for K. wilmsii tubers. Total phenolic content and total flavonoid content analysis proved the presence of high levels of phenolic compounds as well as flavonoids. The presence of phenols and flavonoid could be responsible for the radical scavenging activities observed.