Thyme essential oil loaded microspheres for fish fungal infection: microstructure, in vitro dynamic release and antifungal activity

Abstract

Aims

Evaluate the effect of varying the droplet size of microspheres charged with thyme essential oil (TEO-MS) on their swelling (Sw), release rate (%RR) and in vitro antifungal activity against Saprolegnia sp.

Methods

TEO-MS obtained by ionic gelation were characterised through SEM microscopy and X-ray microtomography. Their Sw and RR% were evaluated at simulated fish-gastrointestinal conditions using gravimetric and spectrophotometric techniques.

Results

For all evaluated droplet sizes (p ≥ 0.05), TEO was heterogeneously distributed inside of the MS and TEO-MS experimented agglomeration and sphericity loss after the drying process. Under gastric conditions, the acid pH (2.9) limited the Sw (50–100%) of TEO-MS, generating a low RR% (14–18%). Contrary, the slightly alkaline intestinal pH (8.1) favoured the Sw (∼3.2 to 3.8 times) and therefore the RR% (42–63%).

Conclusions

TEO-MS (5–100 mg/mL) presented antifungal capacity onto Saprolegnia sp. after the simulated fish digestion, being the small droplet size once the most effective.

Keywords:

• Microspheres
• essential oil
• microstructure
• antifungal capacity

Acknowledgements

The authors would like to thank the Anatomy, Histology and Pathology Department of Universidad Austral de Chile where some experiments were carried out, and Joscelyn Diaz, PhD., for her editorial advice.

Disclosure statement

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

Additional information

Funding

This research was partially funded by Pontificia Universidad Católica de Chile through ‘Proyecto Anillo ACT 1105/2012’ and Universidad Adventista de Chile through ‘Project FAIN 53/2015.’