Abstract
The antioxidant activity of Avicennia alba Blume, (1826) leaf extract was determined using 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 ethanolfree extract (TSB) exhibited antioxidant activity; it showed a color change from purple to light yellow similar to positive control (ascorbic acid solution) and a decrease in absorbance relative to negative control (95% ethanol). The results of the DPPH free radical scavenging activity assay was subjected to statistical analysis using one way ANOVA then post hoc analysis results of TSB showed no significant difference vs positive control, 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 where it 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 were 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 similar color change as 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 to the positive control with the highest antioxidant activity of 87.88% ± 3.357 .The p-value (<0.01) obtained manifested that there was significant difference between the test solutions with their antioxidant activity. After DPPH assay, the most active fractions 1 & 2, were subjected to FT-IR and GC-MS. Infrared spectrum showed the presence of aliphatic C-H bonds, C=O bond, and –OH bonds while the GC-MS analysis revealed five compounds which 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.
Highlights
Medicinal plants have played an essential role on the health and healing of man since the dawn of human civilization (Saikia and Upadhyaya, 2011)
The petroleum ether-free extract (TSA), ethanol-free extract (TSB) and positive control at final concentration of 300 μg/ mL was subjected to DPPH free radical scavenging assay
The absorbance of the negative control showed the highest absorbance reading with mean value of 0.3811 ± 0.086 followed by petroleum etherfree extract at 0.3251 ± 0.113
Summary
Medicinal plants have played an essential role on the health and healing of man since the dawn of human civilization (Saikia and Upadhyaya, 2011). Various and many free radical scavenging antioxidants are found in plants. Antioxidants are vital phytochemicals, vitamins, and other nutrients which protect the body from damages brought about by free-radical induced oxidative stress (Vadlapudi & Naidu, 2009). Antioxidant substances block the harmful action of free radicals by scavenging the free radicals and detoxifying the organism (Dehpour, Ebrahimzadeh, Nabavi, & Nabavi, 2009). In vitro and in vivo studies have shown that antioxidants help prevent the free radical damage that is associated with cancer and heart disease. Antioxidants act as free radical scavengers by preventing and repairing damages caused by reactive oxygen species (ROS), enhancing the immune defense and lowering the risk of cancer and degenerative diseases (Pham-Huy, Hua, & Pham-Huy, 2008 as cited in Ebrahimzadeh, Nabavi, Nabavia, Bahramian, & Bekhradnia, 2010)
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