Phytochemical Characterization, Antioxidant and Antimicrobial Activities of Callistemon Citrinus Leaf Extract

Callistemon citrinus is a medicinal plant rich in bioactive phytochemicals; however, comprehensive studies integrating physicochemical standardization, phytochemical characterization, antioxidant evaluation, and antimicrobial activity of its hydroalcoholic leaf extract remain limited. The present study was undertaken to address this research gap by evaluating the quality parameters and biological activities of C. citrinus leaf extract. Physicochemical analysis revealed acceptable quality standards, including a loss on drying of 6.7%, total ash of 7.6%, alcohol-soluble extractive value of 12.5%, and water-soluble extractive value of 13.8%. Preliminary phytochemical screening confirmed the presence of flavonoids, phenolics, tannins, terpenoids, saponins, and alkaloids. The extract exhibited significant antioxidant activity with IC₅₀ values of 8.14 ± 1.52 μg/mL in the DPPH assay and 7.63 ± 0.63 μg/mL in the ABTS assay, while total phenolic and flavonoid contents were 18.192 ± 0.104 mg GAE/g and 16.351 ± 3.907 mg QE/g, respectively. Antimicrobial evaluation demonstrated concentration-dependent antibacterial activity against Enterococcus and Klebsiella, with maximum inhibition zones of 13 mm and 15 mm, respectively, at 600 mg/mL. These findings demonstrate that the hydroalcoholic leaf extract of C. citrinus possesses appreciable antioxidant and antibacterial activities, primarily due to its phenolic and flavonoid constituents, supporting its potential as a natural source of bioactive compounds for future phytopharmaceutical development.