Chemical and Enantiomeric Profiling of Melaleuca viridiflora Sol. ex Gaertn. Essential Oil and Evaluation of Its Antimicrobial, Antioxidant, and Anticholinesterase Activities

Abstract

Melaleuca viridiflora (niaouli) is an Australian species that has been introduced into different regions worldwide because of its broad adaptability and potential applications. This work aimed to characterize the chemical and enantiomeric composition of the leaf essential oil from M. viridiflora cultivated in the Americas and to explore its biological properties. The essential oil was isolated by steam distillation and chemically characterized using gas chromatographic techniques, while its enantiomeric profile was established using two chiral stationary phases. Biological activity was investigated by determining the antimicrobial effects against a panel of Gram-positive and Gram-negative bacteria, Candida albicans, and Aspergillus niger using the broth microdilution assay. In addition, the antioxidant capacity was examined by ABTS and DPPH radical-scavenging assays, and acetylcholinesterase inhibitory activity was determined by a spectrophotometric method. Fifty compounds were identified, accounting for 99.07% of the total composition. Sesquiterpene hydrocarbons represented the largest group in terms of number of compounds (16), whereas oxygenated monoterpenes predominated in relative abundance (45.27%). The major constituents were 1,8-cineole (35.66 ± 0.37%), viridiflorol (14.20 ± 0.12%), limonene (11.04 ± 0.06%), α-terpineol (7.89 ± 0.71%), and α-pinene (7.42 ± 0.11%). Six pairs of enantiomers were identified. Overall, the essential oil displayed a biological profile characterized by limited antimicrobial and antioxidant effects but a comparatively more pronounced anticholinesterase activity. Antimicrobial effects were observed at 4000 μg/mL against Listeria monocytogenes, Enterococcus faecium, and Aspergillus niger, while antioxidant activity was weak, with an ABTS SC50 of 1.2 mg/mL. In contrast, the oil exhibited moderate anticholinesterase activity, with an IC50 of 65.98 ± 1.0 μg/mL. Taken together, these findings indicate that the biological profile of M. viridiflora essential oil is primarily distinguished by its anticholinesterase activity rather than by antimicrobial or antioxidant effects. This study provides the first report for Melaleuca viridiflora cultivated in the Americas.