Determination of Antioxidant Capacity in Aqueous Extracts of Corymbia citriodora Using DPPH, ABTS, FRAP, TPC, and Hydrogen Peroxide Assays

The increasing interest in natural antioxidants has led to extensive research on plant extracts with potential health benefits. This study evaluates the antioxidant capacity of aqueous extracts of Corymbia citriodora using five different assays: DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging assay, ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging assay, FRAP (Ferric Reducing Antioxidant Power), Total Phenolic Content (TPC) via the Folin-Ciocalteu method, and Hydrogen Peroxide Scavenging assay. The results indicate that the extract possesses significant antioxidant activity with quantifiable dose-dependent responses. DPPH radical scavenging activity increased from 45.6% to 73.2% (60.5% increase) when concentration was raised from 10 to 50 μg/mL at 75°C. Similarly, ABTS activity improved from 42.8% to 72.1% (68.5% increase), while FRAP values enhanced from 110.2 to 160.9 μM Fe²⁺/g (46.0% increase) under the same conditions. Total phenolic content doubled from 24.3 to 49.3 mg GAE/g (102.9% increase), and hydrogen peroxide scavenging capacity increased from 38.4% to 72.6% (89.1% increase). Temperature elevation from 25°C to 75°C resulted in consistent improvements across all assays, with average increases of 11.2% for DPPH, 9.7% for ABTS, 7.7% for FRAP, 17.3% for TPC, and 16.7% for H₂O₂ scavenging at each concentration level. The TPC analysis confirmed the presence of phenolic compounds, correlating with the antioxidant activity. These findings suggest that Corymbia citriodora is a rich source of natural antioxidants, making it a potential candidate for pharmaceutical and nutraceutical applications. Further studies on bioactive compound isolation and in vivo assessments are recommended to explore its full therapeutic potential.