Phytochemical screening and evaluation of <em>in vitro</em> antioxidant activity of different fractions of bark extracts of <em>Stereospermum suaveolens</em>

Purpose: This study aimed at evaluating the antioxidant capacity of methanolic bark extracts and fractions obtained from silica gel column chromatography of the methanolic bark extracts of Stereospermum suaveolens. Methods: Air-dried powdered S. suaveolens bark was extracted with methanol and concentrated to obtain crude extracts. The crude bark extracts and the fractions obtained from silica gel column chromatography were screened for the presence of different groups of phytochemicals and for the determination of antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power assays. Statistical significance was evaluated using an independent sample t-test, and p < 0.05 was considered statistically significant. The half-maximal inhibitory concentration (IC₅₀) values for the DPPH assay were calculated using GraphPad Prism 9 software. Results: The presence of flavonoids, saponins, and phenolic compounds was detected in the bark extracts. The fractionation of the bark extract resulted in seven bark fractions (F1B to F7B), with the highest antioxidant activity detected in the 3rd fraction F3B (82.51%). The ferric reducing antioxidant power assays of both S. suaveolens bark extracts and L-ascorbic acid increased with concentration, and a statistically significant difference (p < 0.05) was observed between the bark extracts of S. suaveolens and L-ascorbic acid, except at a concentration of 15.62 µg/mL. The IC₅₀ values determined using the DPPH method for the methanolic bark extracts of S. suaveolens and L-ascorbic acid were found to be 5.46 ± 0.56 μg/mL and 2.82 ± 0.23 μg/mL, respectively, indicating that the antioxidant activity of L-ascorbic acid was greater than that of the bark extracts (p = 0.0147). Conclusion: The bark extracts and the fractions obtained from column chromatography exhibited antioxidant activity, indicating that the bark of S. suaveolens has the potential to serve as an antioxidant.