Morphological, Optical and Thermal Properties of bioactive-Chitosan Nanostructured Edible Films for Food Packaging Applications

The application of nanostructured edible films is an emerging technology for fruit and vegetables postharvest preservation. These films act as a barrier between the fruit surface and the surrounding environment delaying product ripening; therefore, their characterization is of special interest. In this study, three different nanostructured films based on chitosan nanoparticles, thyme essential oil or propolis-loaded chitosan nanoparticles were prepared. The films were characterized based on their morphology by scanning electron microscopy, crystalline structure by X-ray diffraction, optical properties by ellipsometry, and thermal properties (diffusivity, effusivity, and conductivity) using the photoacoustic technique. Also, wettability, water activity and permeability (water vapor diffusion coefficient) were measured. Aggregates were observed for the propolis-loaded chitosan nanoparticles film by scanning electron microscopy. All three films were semi-crystalline with similar roughness (94.2–95.6%), and thermal parameters values were diffusivity between 1.7 and 2.3 × 10^–6 m²/s, effusivity between 82.57 and 86.01 Ws^1/2/m²K, and conductivity between 0.11 and 0.12 Wm⁻¹ K⁻¹. The chitosan nanoparticles film was the most hydrophobic (37.55°) with the lowest permeability (0.77 × 10^–8 cm² s⁻¹). Bioactive-chitosan nanostructured edible films are a good alternative as food packaging due to their physicochemical, optical and thermal properties for application as a protective barrier for horticultural products.