The present study was aimed to evaluate the efficacy of carboxymethyl cellulose (CMC; 1.25 g)/Persian gum (PG; 0.65 g) bionanocomposite films containing titanium dioxide nanoparticles ( TiO2; 0.5% w/w) and fennel essential oil (FEO; 2% w/v) in preserving the chemical, microbial and sensory properties of rainbow trout fillets during the storage (0, 3, 6, 9 and 12 days) at 4 ± 1 °C. The lowest values for the minimum inhibitory concentration (8 mg/mL) and the minimum bactericidal concentration (10 mg/mL), and the highest diameter of the inhibitory zone in the disc diffusion (19 mm) for CMC/PG/FEO/ TiO2 were observed against Listeria monocytogenes. Moreover, as a microbiological analysis, total viable count (3.01–6.74 log CFU/g), Pseudomonas spp. (3.02–4.86 log CFU/g), lactic acid bacteria (2.02–4.23 log CFU/g), Enterobacteriaceae (2.12–3.99 log CFU/g), and psychrotrophic bacteria (3.42–6.74 log CFU/g) were determined on the rainbow trout fillets covered with different treatments during the storage. Treatments containing FEO and TiO2 had a significant effect on the growth control in the studied bacteria (P < 0.05) and prevented the increase of pH. The amount of thiobarbituric acid (0.13 mgMDA/Kg) increased over time in all treatments, but it was lower in the FEO (0.5 mgMDA/Kg) treatment. Sensory scores of the samples were very high until day 6. In general, the results of this study showed that the use of FEO and TiO2 in the biodegradable films improves the antimicrobial, chemical, and sensory properties of the rainbow trout fillets.

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