Essential oils microemulsions prepared with high-frequency ultrasound: physical properties and antimicrobial activity
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ORIGINAL ARTICLE
Essential oils microemulsions prepared with high-frequency ultrasound: physical properties and antimicrobial activity M. Da´vila-Rodrı´guez1 • A. Lo´pez-Malo1 • E. Palou1 • N. Ramı´rez-Corona1 M. T. Jime´nez-Munguı´a1
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Revised: 19 December 2019 / Accepted: 15 April 2020 Ó Association of Food Scientists & Technologists (India) 2020
Abstract Essential oils (EOs) have demonstrated antimicrobial activity against bacteria due to the effects of their major components. The direct application of EOs may present a rapid volatilization of its components and can decrease their effectiveness. Encapsulation by means of emulsification can provide protection to lipid compounds on a microscale. The aim of this study was to characterize microemulsions of cinnamon essential oil (CEO), oregano essential oil (OEO), and rosemary essential oil (REO) prepared by high-frequency ultrasound and evaluate their antimicrobial activities against Escherichia coli and Listeria monocytogenes. The microemulsions (oil-in-water, O/W) of EOs were prepared using high-frequency ultrasound, applying a wave amplitude of 84 lm for 15 min (REO and CEO) or 30 min (OEO). The antimicrobial activity was determined by inoculating 108 CFU/mL of bacteria. Nonsurvival of the bacteria was confirmed by plate count in tryptic soy agar, determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The microemulsions exhibited droplet size diameters of 1.98 to 5.46 lm, showing high encapsulation efficiencies (79.91–81.97%) and low separation rates (2.50–6.67%). The MIC and MBC for the microemulsions for both bacteria were 20–75% less than values obtained for the non-encapsulated EOs. This study demonstrates that high-frequency ultrasound is a suitable technique for obtaining stable microemulsions to
& M. T. Jime´nez-Munguı´a [email protected] 1
Chemical, Food and Environmental Engineering Department, Universidad de Las Ame´ricas Puebla, Ex-Hacienda Sta. Catarina Ma´rtir S/N, San Andre´s, Cholula, 72810 Puebla, Mexico
deliver natural antimicrobials that can be applied to control bacteria of high relevance in food safety. Keywords Essential oils Encapsulation Antimicrobial activity Microemulsions High-frequency ultrasound
Introduction Recent studies have demonstrated that some essential oils (EOs), such as those of garlic, cinnamon, thyme, oregano, clove, basil, coriander, citrus peel, eucalyptus, ginger, rosemary, and peppermint, among others, have antimicrobial activity against bacteria, yeast, and molds. The hydrophilic or hydrophobic character of the EOs is related to their antimicrobial activity, the proportion of the main components in each of them (terpenoids, phenolics, and aldehyde compounds), and the type of microorganism that they might inhibit or inactivate (Fisher and Phillips 2008). The chemical structure of the components of EOs affects their mode of action as antimicrobials; altering the lipids of the microbial cytoplasmic membrane produces loss of its impermeability to prot
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