Effect of sodium alginate-bentonite nanocomposite films enriched with Satureja hortensis essential oil on extending the shelf-life of rainbow trout fillets

This study evaluated the effects of Satureja hortensis essential oil (SHEO)-enriched sodium alginate-bentonite nanocomposite films on the quality of rainbow trout (Oncorhynchus mykiss) fillets during 15 days of refrigerated storage at 4 +/- 1 degrees C, with analyses conducted on days 0, 3, 6, 9, and 15. Five film formulations were prepared: sodium alginate alone (C), sodium alginate with bentonite nanoclay (CN), and sodium alginate combined with SHEO at 0.5%, 1%, and 1.5% concentrations (CN0.5, CN1, CN1.5). SHEO addition improved film properties, with thickness increasing from 0.225 +/- 0.013 cm in the control to 0.245 +/- 0.014 cm in CN1.5 and tensile strength peaking at 5.37 +/- 0.15 MPa in CN0.5. The CN1.5 group exhibited superior preservation effects, maintaining total viable counts at 4.58 log CFU/g compared to 6.88 log CFU/g in the control by day 15. Pseudomonas spp., coliforms, lactic acid bacteria, and psychrotrophic bacterial counts were significantly reduced. Lipid oxidation was minimised, with thiobarbituric acid reactive substances values of 0.8 mg MDA/kg in CN1.5 compared to 2.38 mg MDA/kg in the control. Additionally, total volatile basic nitrogen levels were maintained at 15.4 mg N/100 g in CN1.5, while they reached 28.4 mg N/100 g in the control. These results highlight the potential of SHEO-enriched sodium alginate-bentonite nanocomposite films, particularly CN1.5, in extending the freshness and shelf life of rainbow trout fillets under refrigerated conditions.