Spray-Dried Eugenol Microparticles: Physicochemical Characterization and Enhanced Antibacterial Activity

Background/Objectives: Antimicrobial resistance is a critical threat to global public health. Eugenol is a bioactive compound with broad-spectrum antimicrobial activity that has attracted increasing interest as a naturally derived antimicrobial agent with potential complementary applications to conventional antibiotics, but its clinical application is severely limited by its high volatility, low water solubility and thermo-oxidative instability. The main objective of this study was to develop eugenol-loaded microparticles using a ternary biopolymer matrix, to characterise their main physicochemical properties, and to evaluate their in vitro antimicrobial efficacy against clinically relevant bacterial reference strains. Methods: The microparticles were formulated from an emulsion of maltodextrin, gum arabic and soy lecithin, and encapsulated using a spray-drying technique. Product recovery, particle morphology assessed by scanning electron microscopy (SEM), particle size distribution determined by laser diffraction, and encapsulation efficiency quantified by GC-FID were analysed. Subsequently, antimicrobial activity was evaluated by comparing the microparticles with free eugenol using agar well diffusion and broth microdilution assays to determine the minimum inhibitory concentration (MIC) against eight bacterial strains. Results: The spray-drying process achieved a product recovery of 61.88% and an encapsulation efficiency of 52.45%. The resulting microparticles exhibited a smooth, spherical morphology with diameters of less than 20 µm. In microbiological assays, microencapsulation significantly reduced MIC values by 4- to 16-fold compared with free eugenol for susceptible strains. The formulation exhibited potent activity against most of the Gram-positive and Gram-negative pathogens tested, except for Pseudomonas aeruginosa, which remained resistant to both formulations. Conclusions: The encapsulation of eugenol in this optimised biopolymer matrix substantially improved its antimicrobial efficacy against the tested bacterial strains. These findings highlight the potential of spray-dried eugenol microparticles as a promising antimicrobial formulation and provide a basis for their further development for topical applications. Further studies are warranted to evaluate their pharmaceutical performance and antimicrobial mechanisms.