Preparation of active/intelligent packaging antibacterial film and hydrogen sulfide-sensitive indicator for trout fillets freshness based on copper nanoparticles

This study introduces an innovative bilayer film developed using bitter vetch seed protein (BVSP)/polylactic acid
(PLA) and copper nanoparticles (CuNPs), targeting shelf-life extension of trout fillets. Preparation of a colori-
metric indicator for spoilage detection was also considered. We explored the impact of CuNPs incorporation on
the physicochemical, structural, and functional attributes of the film. Attenuated total reflectance Fourier
transform infrared analyses showed the electrostatic bond between BVSP and CuNPs, facilitating CuNPs’ inte-
gration into the film matrix. FE-SEM imaging further affirmed a uniform CuNPs dispersion within the matrix.
Remarkably, these interactions enhanced the thermal stability, mechanical attributes and barrier effectiveness of
the films. Tensile strength and water vapor permeability improved in active bilayer films. The incorporation of
CuNPs increased the melting temperature of active bilayer films by 8%. TGA results showed that the weight loss
of bilayer films decreased from 90.54 to 86.78% in bilayer active film at 500 ◦C, showing better thermal stability
of active bilayer film. While the bilayer films had no antibacterial activity against S. aureus and E. coli, the
incorporation of CuNPs caused an outstanding antibacterial activity in active bilayer films. On the other hand,
the addition of CuNPs to the filter paper demonstrated an intense sensitivity to hydrogen sulfide (H2S) gas,
signaling fish spoilage by color transitioning from white to brown. Packaged trout fillets in designed active films
improved their shelf life from 7 to 10 days of storage in the refrigerator. The designed films hold significant
promise as novel solutions for active and intelligent food packaging, offering dual benefits of antimicrobial
protection and spoilage indication.