Thermal, structural, antimicrobial, and physicochemical characterisation of thyme essential oil encapsulated in β- and γ-cyclodextrin

Abstract

The present work aimed to encapsulate the thyme essential oil (TEO) in β-cyclodextrin (BCD) and γ-cyclodextrin (GCD) complexes in two selected cyclodextrin (CD) to TEO ratios (85/15 and 80/20 w/w) and compare the physicochemical, antioxidant, and antimicrobial properties of the encapsulated powders. The inclusion complexes between CD and TEO were prepared by blending aqueous CD and TEO in ethanol followed by freeze-drying. The powder properties were assessed by measuring particle size and microstructure using SEM, FTIR, and XRD. The median values of the particle sizes (GCD: 92.0 ± 4.69 and BCD: 46.2 ± 2.56-mm) significantly influenced the encapsulation efficiency, resulting in a higher encapsulation efficiency of the GCD (92.02 ± 10.79%) than that of the BCD (56.30 ± 12.19%). The encapsulated GCD/TEO (80/20) showed higher antioxidant activity and an antimicrobial inhibitory effect against Listeria monocytogenes and Salmonella enterica sv. typhimurium. Overall, the GCD acts as a superior wall material to the BCD in the TEO encapsulation.

Keywords:

• Encapsulation
• β-cyclodextrin
• γ-cyclodextrin
• thyme essential oil
• freeze drying
• particle size distribution
• anti-microbial activity

Acknowledgements

The authors are thankful to Professor Rafael Auras, Michigan State University, USA for providing β- and γ-cyclodextrin samples.

Author contributions

Jasim Ahmed: conceptualisation, methodology, formal analysis, resources, writing—review and editing, supervision, and project administration. M. Z. Mulla: formal analysis and writing. H. Al-Attar: SEM and DSC analysis. S. AlZuwayed and A. Joseph: TGA analysis. Harsha Jacob: microbiological analysis. M. Ejaz, S. Al-Jassar, L. Thomas, and N. Al-Ruwaih: sample preparation/formal analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author expresses their gratitude to the Kuwait Foundation for the Advancement of Sciences (KFAS) and Kuwait Institute for Scientific Research for providing the grant for the research work (Grant number FB133C).