Beet Root Peel Extract as a Natural Cost‐Effective <scp>pH</scp> Indicator and Food Preservative in Edible Film: Shelf Life Improvement of Cold‐Stored Trout Fillet

In this study, chitosan (C)-polyvinyl alcohol (P) edible film containing bio-fabricated nanosilver particles (nAg) (as antimicrobial agent) and beetroot peel extract (BRPE) (as antioxidant agent and pH indicator) was used as spoilage indicator in cold-stored rainbow trout fillets. DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity (43.02%), reducing power (2.87), and total phenolic content (360.50 mg GAE/g) of ethanolic BRPE were higher than aqueous extract. Silver nanoparticles were biosynthesized using silver nitrate reduction by chitosan, confirmed by UV-Visible spectroscopy, optical and scanning electron microscope images, and X-ray diffraction analysis. The highest tensile strength (4.20 MPa) and elongation at break (118%) belonged to the CP-BRPE film, and the lowest water vapor permeability (2.45 10^-5 g/s/m/P) was related to the CP-nAg film. Also, the lowest total viable count (6.17 log CFU/g), psychrotrophic bacteria (6.27 log CFU/g), <i>Enterobacteriaceae</i> (4.9 log CFU/g), pH (5.66), total volatile basic-nitrogen (TVB-N) (22.1 mg/100 g of fish), and thiobarbituric acid reactive substances (TBARS) (0.705 mg MDA/kg of fish) values of the packaged trout fillets were significantly (<i>p</i> ≤ 0.05) observed in CP-BRPE-gnAg treatment among the other treatments at the end of the storage period, and CP-gnAg, CP-BRPE, and CP treatments were in the next ranks, respectively. Colorimetric analysis of the used films showed that the films containing BRPE depicted color spectra of red to yellow at the same time as the spoilage symptoms initiated in the packaged fillets. It is concluded that BRPE not only increased the preservative effects of chitosan-polyvinyl alcohol film containing green silver nanoparticles but also can be considered as a natural cost-effective spoilage indicator of the rainbow trout fillets during cold storage time.