In vitro antioxidant activity of secondary metabolites of Aspergillus fumigatus isolated from Piliostigma thonningii

Abstract

Plant endophytic fungi are novel reservoirs of bioactive compounds. This study aims to explore the antioxidant activity of the secondary metabolites (SM) of an endophytic fungus isolated from the leaves of Piliostigma thonningii plant. An endophytic fungus (coded EDP 1) was isolated, purified, and identified. The pure endophyte was fermented, its crude SM extracted and screened for antioxidant activities using 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. With an IC₅₀ value of 18.84, the SM of the endophytic fungus (Aspergillus fumigatus) demonstrated significant antioxidant activity compared to 5.79 µg/mL recorded for ascorbic acid. The SM and ascorbic acid showed free radical scavenging activity of 77.67; 85.67% and 68.50; 88.76% in the DPPH and FRAP assays, respectively. Using gallic acid (R² = 0.991) and quercetin equivalent (R² = 0.986) standard plots, the total phenolic and flavonoid contents were found to be 228.88 ± 1.12 mg GAE/g and 152.56 ± 1.27 mgQE/g, thus suggesting phenolic and flavonoid-related antioxidant activity of the SM. This study showed that the SM of A. fumigates has promising antioxidant properties, which could be explored further for their pharmacological applications.