Encapsulation of Oregano (Origanum vulgare L.) essential oil into β-cyclodextrin and lipidic dispersions: Characterization and Evaluation of their antimicrobial activity against Listeria monocytogenes in broth and model food

The hydrophobicity, strong flavor and high volatility of essential oils impede their commercial application in foods. As such, we aimed to study the encapsulation of Oregano essential oil (OEO) in β-cyclodextrin (β-CD) and lipidic dispersions as means to enhance dispersion and controlled release of EO and evaluate their effect on the survival of Listeria monocytogenes in Tryptic Soy Broth (TSB) and cheese broth.

The encapsulation of OEO in β-CD was performed with the co-precipitation method, whereas for the incorporation of OEO into lipidic dispersion the thin-film hydration method was applied. Size distribution (PDI) and zeta-potential (ζ) of the formed inclusion complexes (IC) were assessed by Dynamic Light Scattering (DLS). UV-Vis spectroscopy was used for the determination of the encapsulation efficiency (EE%) and for assessing the release rate of the formed IC. The effect of ICs and free OEO at MIC, ½ MIC and 2xMIC against L. monocytogenes (3-strain cocktail: 10⁶ CFU/ml), was determined in TSB (pH 7.0, 4.3) and cheese broth prepared from ‘katiki’ (pH 4.3) at 7^oC.

The complexes presented nanoscale size (<1000 nm), 127.24 ±25.83 nm with an intensity of >90% for OEO-β-CD and 106.84 ±42.81 and 948.05 ±409.95 nm with intensity of 47% and 51.9%, respectively for OEO-lipidic dispersion. The size dispersion was 0.433 ±0.064 nm for OEO-β-CD and 0.872 ± 0.070 nm for OEO-lipidic dispersion. An acceptable stability was observed (>20 mV) with ζ-potential -23.57 ±6.76 mV for OEO-β-CD and -49.5 ± 6.18 mV for lipidic dispersion. EE% was 80.3% ± 4.0 and 87.8 ± 3.7 for OEO-β-CD and OEO-lipidic dispersion, respectively. The OEO release from both complexes occurred continuously for 18 days. The dose-dependent inhibitory effect of encapsulated OEO against L. monocytogenes was higher in TSB than in cheese-broth and increased at lower pH.  Lipidic dispersion was more effective than OEO-β-CD at both pH values. The antimicrobial effect of encapsulated OEO was not as rapid as the effect of free EO, confirming the slow release of EO due to encapsulation. The results are indicative for the application of encapsulated OEO to control of L. monocytogenes in foods.