Design, Fabrication, and Evaluation of Solid Lipid Nanoparticles Containing <i>Ferula assa</i>-Foetida Essential Oil as an Antimicrobial Agent Against Human Pathogens

Abstract

Background: Ferula assa-foetida essential oil has demonstrated antimicrobial activity, making it a promising candidate for plant-derived antimicrobial formulations. However, poor aqueous solubility, volatility, and instability may limit the application of essential oils. Encapsulation in solid lipid nanoparticles (SLNs) may help overcome these limitations and improve antimicrobial delivery. This study aimed to formulate and characterize SLNs containing F. assa-foetida essential oil and to evaluate their antibacterial activity against foodborne pathogens. Objectives: This study aimed to design, fabricate, and evaluate solid lipid nanoparticles containing F. assa-foetida essential oil as an antimicrobial agent against foodborne pathogens. Methods: Lipids were heated to 5 - 10 °C above their melting point. Lipophilic substances were added to the lipid phase, and hydrophilic substances were added to the aqueous phase. Both phases were maintained at the same temperature in a water bath. The aqueous phase was added to the lipid phase to form a pre-emulsion, which was homogenized using an Ultratorex homogenizer and then reduced to fine particles using an ultrasound device. SLN formation at room temperature required approximately 4 - 12 hours and, in some cases, up to 24 hours. Fourier transform infrared spectroscopy and electron microscopy analyses were then performed, and incubation rates were assessed. The antimicrobial properties of the SLNs were assessed using antibacterial methods. Results: The spectrum obtained by Fourier transform infrared spectroscopy for SLNs containing F. assa-foetida essential oil showed functional groups associated with the lipid matrix and the active compounds of the essential oil, including phenolic and alcoholic compounds and hydrogen-bonding interactions. The differential thermal analysis (DTA) plot showed three main thermal events. A small change at approximately 25.5 °C, with a negative heat change, was attributed to the release of moisture or volatile compounds. The event at 262.2 °C could reflect the onset of decomposition of light organic compounds and plant components of the F. assa-foetida essential oil. The main broad peak began at 485.5 °C and peaked at approximately 560 - 570 °C, corresponding to major decomposition of organic compounds and the lipid matrix. Overall, DTA indicated relative stability up to intermediate temperatures and major degradation at high temperatures. The SLNs produced inhibition halos and showed good inhibitory activity against foodborne pathogenic bacteria. Conclusions: Physicochemical evaluation of the nanosystem after loading F. assa-foetida essential oil into SLNs showed that the system was anionic and exhibited slow-release behavior. Its particle size, appropriate morphology, and acceptable essential oil uptake rate indicated its suitability as a carrier for F. assa-foetida essential oil, thereby increasing the essential oil’s stability and solubility and consequently improving its performance.