Can droplet size influence antibacterial activity in ultrasound-prepared essential oil nanoemulsions?

Abstract

Essential oil nanoemulsion may have improved antibacterial properties over pure oil and can be used for food preservation. Ultrasonic cavitation is the most common mechanism for producing nanoemulsions, and the impact of processing parameters on droplet properties needs to be elucidated. A systematic literature search was performed in four databases (Science Direct, Web of Science, Scopus and PubMed), and 987 articles were found, 16 of which were eligible for the present study. A meta-analysis was performed to qualitatively assess which process parameters (power, sonication time, essential oil, and tween 80 concentration) can influence the final droplet size and polydispersity and how droplet size is associated with antibacterial activity. We observed that power, essential oil, and tween 80 concentrations added during processing are the critical variables for forming smaller droplets. Ratios of up to 3:1 (surfactant:oil) can produce droplets smaller than 180 nm with antibacterial properties superior to pure oil or isolated compounds. The improved properties of nanoemulsions are associated with the size and chemical composition of the droplet since the proportion of the hydrophobic core (EO) and the hydrophilic outer layer (Tween 80) directly influences the antibacterial mechanism of action.

Keywords:

• Emerging technology
• natural antimicrobial
• nanotechnology
• sonication
• Tween 80

Acknowledgements

The authors are thankful for the financial support provided by the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro — grant number [E-26/203.049/2017] and [E‐26/010.000.984/2019], the Fundação de Amparo à Pesquisa e Inovação do Espírito Santo grant number [533/2020], the Conselho Nacional de Desenvolvimento Científico e Tecnológico - grant number [300968/2021-3] and [140873/2021-0].

Disclosure statement

The authors declare no conflict of interest.