Aloe ferox Mill. (Asphodelaceae) is used in South Africa for the treatment of constipation among various ailments. Despite the extensive studies conducted on the antioxidant activities of the leaf gel and pulp extract of the plant, there is no information on the antioxidant properties of the whole leaf extract of the species.
The antioxidant activities of ethanol, acetone, methanol and aqueous extracts of A. ferox were investigated spectrophotometrically against 1,1- diphenyl-2-picrylhydrazyl (DPPH), 2,2’-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) diammonium salt, hydrogen peroxide (H 2O 2), nitric oxide (NO), lipid peroxidation and ferric reducing power. Total phenols, flavonoids, flavonols, proanthocyanidins, tannins, alkaloids and saponins were also determined using the standard methods.
The percentage compositions of phenols (70.33), flavonols (35.2), proanthocyanidins (171.06) and alkaloids (60.9) were significantly high in the acetone extract, followed by the ethanol extract with values of 70.24, 12.53, 76.7 and 23.76 respectively, while the least composition was found in the aqueous extract. Moreover, both flavonoids and saponins contents were appreciably high in both methanol and ethanol extracts, while others were very low. Tannins levels were, however, not significantly different ( P > 0.05) in all the solvent extracts. At 0.5 mg/ml, the free radical scavenging activity of the methanol, acetone and ethanol extracts showed higher inhibition against ABTS, hydrogen peroxide and nitric oxide radicals. Whereas, scavenging activity of the extracts against DPPH* and lipid peroxidation were observed at a concentration of 0.016 and 0.118 mg/ml respectively in comparison to the butylated hydroxyltoluene (BHT), gallic acid and rutin. The ferric reducing potential of the extracts was concentration dependent and significantly different from that of vitamin C and BHT.
The present study showed high level of radical scavenging activity by ethanol and methanol whole leaf extracts of A. ferox with higher antioxidant activities than acetone and aqueous extracts. The significant differences show that the whole leaf extract could be used as a potent antioxidant in medicine and food industries.