Physicochemical characterization and antimicrobial activity of edible propolis-chitosan nanoparticle films

The aim of this study was to evaluate the physicochemical properties and antimicrobial activity of edible propolis-chitosan nanoparticle films. Five formulations containing chitosan (C1), chitosan nanoparticles (C2) and ethanolic extract of propolis (EEP) at different concentrations (C3 = 10%, C4 = 20% and C5 = 30%) were prepared. From the results, a particle size of 28.42 ± 7.43 nm was observed from transmission electron microscopy (TEM) micrographs for chitosan nanoparticles (CSNPs). Contact angle measurements showed a more hydrophilic (0°) behavior for C1 and C4. On the other hand, the most hydrophobic behavior was observed for C3 and C5, with values of 21.38° and 21.17°, respectively. Optical micrographs of coated strawberries showed good adhesion with thickness values between 146.15 and 341.88 μm. No significant differences were found for moisture content, hardness and X-ray diffraction (XRD) (p < 0.05). When nanoparticles were incorporated into the formulations and propolis content increased, the degree of swelling and water solubility decreased. Fourier-transform infrared spectroscopy (FTIR) spectra revealed possible interactions among components. From the micromechanical tests, the highest value of elastic modulus (2.6 GPa) was obtained for C3. From AFM studies, the addition of chitosan nanoparticles and propolis decreased the value of roughness. The antibacterial activity evaluation showed that after 24 h, the propolis-containing formulations (C3-C5) had a strong inhibitory effect on Listeria monocytogenes and C3 on Escherichia coli. The use of chitosan nanoparticles and ethanolic extract of propolis in edible films is a promising alternative for active packaging with antibacterial properties in view of their application for the preservation of strawberries against foodborne bacteria.