Process optimization and stability enhancement of Origanum vulgare L. essential oil-loaded nanostructured lipid carriers

This study optimized the formulation parameters of nanostructured lipid carriers (NLCs) loaded with Origanum vulgare L. essential oil (OEO), produced by hot emulsification followed by sonication. Phase separation with heating at 60–70°C for 10 minutes yielded nanoparticles with a mean diameter of 102.0 ± 3.8 nm, polydispersity index (PdI) of 0.16 ± 0.01, and zeta potential of −26.43 ± 0.09 mV. Sonication power (60–80%) and processing time (≤ 5 min/mL) were critical to maintaining particle size below 130 nm and PdI below 0.225; powers exceeding 80% induced particle re-aggregation. Laboratory-scale volume increased from 1 to 10 mL, and comparisons between different sonication probe types required fine-tuning of processing parameters. Fourier-transform infrared spectroscopy (FTIR) suggested successful incorporation of OEO into the lipid matrix, with no significant band shifts indicating the absence of strong covalent or ionic interactions between the oil and the lipid components, with an encapsulation efficiency of 99%. DSC/DTG analyses demonstrated thermal stability up to 200°C and the preservation of a crystalline lipid matrix. Storage under refrigeration (4–7°C) maintained the physicochemical integrity of the formulations over 60 days, whereas ambient temperature promoted aggregation. Interaction with collagen produced moderate shifts in PdI and zeta potential without significant aggregation. Overall, the formulation demonstrated favorable physicochemical characteristics that justify future biological evaluation.