In vitro evaluation of the antioxidant potential, phenolic and flavonoid contents of the stem bark ethanol extract of Anogeissus leiocarpus

Abstract

Plant-derived antioxidants with free radical scavenging activities can be relevant as chemopreventive agents against the numerous diseases associated with free radicals and reactive oxygen species. Some phytoconstituents possess antioxidant activities in biological systems. On this basis, we evaluated the antioxidant potential, and determined the total phenolic and flavonoid contents of the ethanol extract of the stem bark of Anogeissus leiocarpus [EESAL]. Antioxidant assays carried out include: 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, phosphomolybdate, β-carotene bleaching, ferric reducing, and hydroxyl radical scavenging activities. Results of DPPH assay showed no significant difference (p < 0.001) between EESAL and butylated hydroxyanisole [BHA], while EESAL exhibited a significantly (p < 0.001) higher activity than BHT [butylated hydroxytoluene]. Phosphomolybdate method recorded a total antioxidant capacity of 190.00 ± 70.53 µg butylated hydroxytoluene equivalents [BHTE]/mg dry extract, while β-carotene bleaching assay gave percent antioxidant activities of both EESAL and BHT as 81.46±1.62 and 80.90±1.39 respectively. Ferric reducing abilities of both EESAL and ascorbic acid increased in a concentration-dependent manner with EESAL displaying a significantly (p < 0.001) higher reductive activity than vitamin C. EESAL displayed a significantly higher hydroxyl radical scavenging activity as compared with BHT at the lowest concentration with no significant difference at the highest concentration. Total phenolic and flavonoid contents of EESAL were obtained as 608.10 ± 2.12 µg GAE/mg and 78.96 ± 3.37 µg QE/mg respectively. Taken together, the free radical scavenging and antioxidant activity of EESAL is likely due to its high phenolic content with complementary effects of the flavonoid components.

Keywords: Anogeissus leiocarpus; BHA; BHT; DPPH; antioxidants; free-radicals.

Figure 1

The percent DPPH radical inhibition of BHA, BHT and EESAL. Values are the average of triplicate experiments.

Figure 2

IC 50 values of EESAL, and the standards (BHA and BHT).

Figure 3

Degradation rate of EESAL assayed by β-carotene bleaching method. Each point represents the average of triplicate values.

Figure 4

Antioxidant activity (%) of EESAL assayed by β-carotene–linoleate bleaching. Values are mean ± SD for triplicate assay. *Significantly different (p< 0.001).

Figure 5

Antioxidant activity of EESAL measured by the reducing power method. Ascorbic acid was used as a positive control. Each absorbance value represents the average of triplicates of different samples analysed.

Figure 6

Hydroxyl radical scavenging activity of EESAL and the positive control [BHT]. All values are reported as means ± SD (n = 3).