Bioactive Potential of Melaleuca Alternifolia: In Vitro Assessment of Antioxidant, Antimicrobial, and Anti-Parkinsonian Activities

Abstract

Melaleuca alternifolia (tea tree) essential oil is a rich source of bioactive terpenoids with promising antioxidant, antimicrobial, and neuroprotective properties. The present study investigated the phytochemical composition, antioxidant, antimicrobial, and in vitro neuroprotective potential of M. alternifolia essential oil. Essential oil was extracted from shade-dried leaves by hydrodistillation using a Clevenger-type apparatus, yielding 0.53% (w/w) oil. Preliminary phytochemical screening and GC–MS analysis were performed to identify major constituents. Antioxidant activity was evaluated using the Ferric Reducing Antioxidant Power (FRAP) assay. Neuroprotective potential was assessed using the MTT assay on SH-SY5Y human neuroblastoma cells and the monoamine oxidase (MAO-A/B) inhibition assay. Antimicrobial activity was determined against Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Candida albicans using the agar well diffusion method. Phytochemical screening confirmed the presence of steroids, flavonoids, phenols, tannins, saponins, glycosides, and proteins. GC–MS analysis identified 42 volatile compounds, with eugenol (43.52%), β-caryophyllene (19.51%), γ-terpinene dimer (17.72%), α-selinene (2.78%), and γ-muurolene (2.35%) as the predominant constituents. The essential oil exhibited potent antioxidant activity with a FRAP IC₅₀ of 0.01316 µL/mL. In the MTT assay, the essential oil demonstrated moderate cytotoxicity toward SH-SY5Y cells (IC₅₀ = 68.69 ± 0.05 µg/mL) compared with doxorubicin (48.62 ± 0.04 µg/mL). However, it showed negligible MAO inhibitory activity, with an IC₅₀ above the maximum tested concentration. The essential oil displayed concentration-dependent antimicrobial activity, with stronger antifungal effects against A. niger and C. albicans than antibacterial effects against S. aureus and E. coli.Melaleuca alternifolia essential oil possesses significant antioxidant and broad-spectrum antimicrobial activities together with moderate neuroprotective potential, supporting its potential as a natural therapeutic candidate for managing oxidative stress-associated disorders and microbial infections.