Chemical composition, antimicrobial and larvicidal properties of Eucalyptus grandis × E. urophylla leaf extracts obtained via hydrodistillation and supercritical carbon dioxide fluid extraction

Yip, See Cheng (2026) Chemical composition, antimicrobial and larvicidal properties of Eucalyptus grandis × E. urophylla leaf extracts obtained via hydrodistillation and supercritical carbon dioxide fluid extraction. Master dissertation/thesis, UTAR.

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Abstract

The leaves of Eucalyptus grandis × Eucalyptus urophylla, a post-harvest residue from Malaysian timber plantations, are rich in bioactive compounds. This study evaluated the chemical composition, antimicrobial activity, mosquito larvicidal efficacy, and toxicity of leaf extracts obtained via hydrodistillation and supercritical carbon dioxide fluid extraction (SCE) from Eucalyptus hybrid trees of two age groups (17 to 31 months and 40 to 50 months). Optimal SCE conditions, identified using response surface methodology, were 79.8°C, 29.7 MPa, 116.2 min (younger trees) and 79.6°C, 30.0 MPa, 108.6 min (older trees). SCE (0.255% to 4.650% w/w) yielded significantly higher percentages than dried leaf hydrodistillation (0.191% w/w for younger trees; 0.046% w/w for older trees), with younger trees consistently producing higher yields across methods. Gas chromatography-mass spectrometry revealed that SCE extracts contained a broader range of chemical classes, including flavonoids, fatty alcohols, fatty aldehydes, and fatty acids. In contrast, hydrodistillation extracts were dominated by monoterpenoids, especially eucalyptol (10.10% to 26.67%) and α-terpinyl acetate (18.27% to 27.99%), with a time-dependent shift towards sesquiterpenes and sesquiterpenoids. Bioassays demonstrated that SCE extracts exhibited stronger and broader-spectrum antimicrobial activity, inhibiting or killing most fungi and bacteria, including antibiotic-resistant clinical strains, at concentrations as low as 0.02 to 2.50 mg/mL. Conversely, hydrodistillation extracts displayed superior mosquito larvicidal activity against Aedes aegypti and Aedes albopictus, with median lethal concentration (LC₅₀) values ranging from 52.26 to 134.56 μg/mL after 24 h, which were lower than those observed in the brine shrimp lethality assay (LC₅₀ = 209.24 to 222.24 μg/mL), indicating their potential for safe aquatic mosquito control. The findings of this study support the possible use of Eucalyptus SCE extracts as disinfectant and hydrodistillation extracts as natural mosquito larvicides, highlighting the valorisation potential of Eucalyptus hybrid leaf waste in agro-industrial applications. Future toxicological and mechanistic studies are required to develop safe formulations for practical applications.

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