Preparation and characterization of gellan gum-chitosan polyelectrolyte complex films with the incorporation of thyme essential oil nanoemulsion

Antimicrobial food packaging with a sustained release of antimicrobial agents plays a key role in maintaining food quality and food safety. In this study, polyelectrolyte gellan gum (GG)-chitosan (CS) multilayer film was fabricated by layer-by-layer assembly technology with the incorporation of thyme essential oil (TEO) coarse emulsion (TEOC) or nanoemulsion (TEON). The microstructure of GG-CS three-layered film was observed by scanning electron microscopy (SEM). The red fluorescent signals in confocal laser scanning microscopy (CLSM) images indicated smaller droplets and more uniform distribution of TEON prepared by ultrasonic treatments, which was consistent with the particle size results and porous structure in SEM images. The film incorporated with 6% TEON exhibited higher antimicrobial activity than that with 6% TEOC, and it significantly reduced E. coli populations in liquid model system. Moreover, films incorporated with TEON showed improved mechanical flexibility (elongation at break) and UV blocking property in comparison to TEOC. This developed GG-CS three-layered film loading with TEON was expected to be a potential antimicrobial material with sustained release property for food packaging applications.