Fabrication and characterization of bio-polymer-based flavonoid nanoemulsion/TiO₂ nanoparticles bilayer composite...

In this study, flavonoid nanoemulsions (FN) were prepared by extracting flavonoids from daylilies, and their particle size, zeta potential, apparent viscosity, and antioxidant activity were characterized. Subsequently, double-layer composite films were fabricated via a layer-by-layer assembly method using carrageenan (CG) and FN as the inner layer, and chitosan (CS), gelatin (GEL), and titanium dioxide nanoparticles (TiO₂NPs) as the outer layer. The results showed that the nanoemulsions containing a flavonoid concentration of 0.8 mg/mL exhibited the smallest particle size (76.84 nm), the highest absolute Zeta potential (20.07 mV), optimal stability, and excellent antioxidant activity. Further, the morphological and storage stability analyses of the 0.8 mg/mL flavonoid nanoemulsion revealed its excellent dispersion and storage stability. In bilayer composite films, the incorporation of FN increased the moisture content to 38.6% and film thickness to 0.094 mm (P < 0.05). The incorporation of TiO₂NPs reduced the moisture content of the composite film from 38.6% to 30.8%, significantly increased its water contact angle and L^⁎ value, and decreased its transmittance (P < 0.05). Furthermore, scanning electron microscopy revealed that the addition of FN and TiO₂NPs reduced the smoothness of the film surface. Moreover, the incorporation of FN and TiO₂NPs effectively enhanced the antioxidant and antibacterial properties of the film. Furthermore, the composite film containing FN and TiO₂NPs significantly inhibited the lipid oxidation of mutton and maintained the total volatile basic nitrogen value within a safe range, indicating that the composite film has potential in the field of food packaging.