Evaluation of Antioxidant Activity of Methanol Extract of Neem Leaves (Azadirachta indica) Using DPPH, ABTS, and FRAP Methods

Background; Azadirachta indica A. Juss (neem) leaves are known to contain various bioactive compounds with potential antioxidant properties. This study aimed to evaluate the antioxidant activity of neem leaf methanol extract through three different in vitro assays DPPH, ABTS, and FRAP while also identifying its secondary metabolite constituents. Methods; Neem leaves were extracted using the Ultrasound-Assisted Extraction (UAE) method with methanol as the solvent in a 1:20 ratio. Phytochemical screening was subsequently performed to identify secondary metabolites. Antioxidant activity was assessed using DPPH, ABTS, and FRAP assays, with absorbance values measured by a microplate reader. IC₅₀ values were determined through non-linear regression analysis of percent inhibition versus sample concentration. Results; Phytochemical analysis confirmed the presence of flavonoids, phenolics, alkaloids, and terpenoids in the methanol extract. The extract exhibited strong antioxidant activity in the DPPH assay, with an IC₅₀ value of 54.91 ppm. In contrast, ABTS and FRAP assays did not demonstrate sufficient antioxidant activity to allow calculation of IC₅₀ or RP₅₀ values, even at concentrations up to 1000 ppm, suggesting limited electron transferbased antioxidant capacity. Conclusion; The methanol extract of A. indica leaves demonstrates considerable antioxidant potential, primarily through the hydrogen atom transfer (HAT) mechanism. Flavonoid and phenolic compounds are likely the major contributors to this activity, supporting the potential of neem leaves as a natural source of antioxidants.