Preparation and comparison of two functional nanoparticle-based bilayers reinforced with a κ-carrageenan-anthocyanin complex

In the present study, two pH-sensitive bilayer films were developed and compared. Agar matrix incorporated with ZnO nanoparticles (NPs) or TiO₂ NPs were combined with the infrastructure of a κ-carrageenan-Clitoria ternatea Linn anthocyanin (CA-CTLA) layer, denoted as AG-ZnO/CA-CTLA film and AG-TiO₂/CA-CTLA film, respectively. The CA-CTLA layer was defined as the sensing layer, whereas the AG-TiO₂ (or AG-ZnO) layer was the protective layer that enhanced the mechanical properties and colour stability. The AG-TiO₂/CA-CTLA film displayed superior UV-vis light barrier property, pH sensitivity, and physical properties. The film's elongation at break and water vapour permeability were 57.08%, and 2.72 × 10^-6 g.m^-1.h^-1.pa^-1, respectively. Notably, the AG-TiO₂/CA-CTLA film possessed the highest UV-vis light barrier properties, and the transmittance was close to 0 in the UV region. Furthermore, these films exhibited visual colour changes in the buffer solution (pH 2.0-12.0), ammonia vapour (80 M), and pork spoilage trials. Therefore, the bilayer films have promising properties for food packaging, especially the AG-TiO₂ NPs/CA-CTLA film.