Chemical composition and antimicrobial activity of Eucalyptus radiata leaf essential oil, sampled over a year

Abstract

This study investigated the seasonal variation of the chemical composition and antimicrobial activity of Eucalyptus radiata leaf essential oil. Young and mature Eucalyptus radiata leaf material was collected monthly (January 2014 to December 2014), hydrodistilled and analyzed using GC-MS. Essential oil yields ranged from 0.14% to 4.31% (w/w). The major compounds were 1,8-cineole (65.7% ± 9.5), α-terpineol (12.8% ± 4.4) and limonene (6.5% ± 2.4). Chemometric tools were used to determine seasonal variations, which showed slight variance in E. radiata chemistry between seasons. The minimum inhibitory concentration (MIC) assay showed that the highest activity was noted against the Streptococci (0.19–2.00 mg/mL) and Lactobacillus acidophilus (0.19–1.75 mg/mL). The activity of the E. radiata leaf essential oil is dependent on the unique ratio of its compounds. The E. radiata leaf essential oil showed good oil yields, a relatively consistent chemical profile and noteworthy antimicrobial activity that rivals other commercial Eucalypt counterparts.

Keywords:

• Seasonal variation
• South Africa
• chemometric analysis
• major compound
• MIC

Acknowledgments

The authors would like to thank the National Research Foundation (NRF) and the Faculty Research Committee (FRC) (Faculty of Health Sciences, University of the Witwatersrand) for financial assistance towards this research. Thanks to the University of the Witwatersrand and Tshwane University of Technology for the infrastructural support and for the resources provided for this research. Mr. Bruce Stumbles is acknowledged for the continual and timely supply of plant material used in this study.