Antioxidant Activity of Avicennia alba Blume, (1826) Family Avicenniaceae, Leaf Extracts Using DPPH Assay

The antioxidant activity of Avicennia alba Blume, (1826) leaf extract was determined using the 1,1-Diphenyl-2-picrylhydrazyl (DPPH) Free Radical Scavenging Activity Assay. Petroleum ether and 95 % ethanol were used as solvents in two separate macerations. Only the ethanol-free extract (TSB) exhibited antioxidant activity; it showed a color change from purple to light yellow similar to the positive control (ascorbic acid solution) and a decrease in absorbance relative to the negative control (95% ethanol). The results of the DPPH free radical scavenging activity assay were subjected to statistical analysis using one-way ANOVA then post hoc analysis results of TSB showed no significant difference vs positive control, with a percentage antioxidant activity of 68.24% ± 12.23 and 76.43% ± 9.22 respectively. The ethanol-free extract (TSB) underwent phytochemical screening by test tube method which revealed the presence of saponins, tannins, flavonoids, and glycosides. It was then subjected to column chromatography for partial purification of its chemical compounds; fractions from the eulates were collected and pooled according to their TLC profile specifically Rf values. The fractions that showed significant spots under UV light were fractions 1 and 2, and fractions 4 and 5. These two sets of fractions were tested to DPPH free radical scavenging assay. Both fractions showed a similar color change to the positive control and a decrease in absorbance relative to the negative control. Fractions 1&2 showed 69.97% ± 2.439 percentage antioxidant activity which had no significant difference from the positive control with the highest antioxidant activity of 87.88% ± 3.357. The p-value (<0.01) obtained manifested that there was a significant difference between the test solutions with their antioxidant activity. After the DPPH assay, the most active fractions 1 & 2, were subjected to FT-IR and GC-MS. The infrared spectrum showed the presence of aliphatic C-H bonds, C=O bonds, and –OH bonds while the GC-MS analysis revealed five compounds that were based on the molecular ion showed at m/z = 537.4. The functional groups present in the compounds from FT-IR and GC-MS analyses and the secondary metabolites present in phytochemical screening seemed to be responsible for the antioxidant activity of Avicennia alba leaf extracts.