A new active nanocomposite film based on PLA/ZnO nanoparticle/essential oils for the preservation of refrigerated Otolithes ruber fillets

In the current study, the active packaging films based on poly lactic acid (PLA) containing 1.5% w/w zinc oxide (ZnO) nanoparticles and varying concentrations (0.5, 1, 1.5% w/w) of Zataria multiflora Boiss. essential oil (ZEO) and Menthe piperita L. essential oil (MEO) were produced. The efficacies of the resulted active films on shelf life extension of Otolithes ruber fish during 16 days of refrigerated storage (4 +/- 1 degrees C) were evaluated. The antibacterial activity of the films was tested against five common food-borne pathogens (Escherichia coll., Salmonella enterica, Pseudomonas aeruginosa, Bacillus cereus and Staphylococcus aureus) by disc diffusion method. The fillet samples were analyzed periodically for microbiological (aerobic count, Enterobacteriaceae count, Pseudomonas spp., Lactic acid bacteria (LAB) count and H2S-producing bacteria) and chemical (TBARS and TVB-N). PLA/ZnO/ZEO and PLA/ZnO/MEO films showed enhanced antibacterial (691 and 513.33 mm(2), repectively, against S. aureus) and antioxidant (69.14 and 49.08%, repectively) activity than control. Based on the microbial count, the active films significantly increased the shelf life of fillets from 8 to 16 days. The lowest TBARS (0.8 mg MA/kg muscle) and TVB-N (21.23 mg/100 g muccle) values were obtained in fillets wrapped with PLA/ZnO containing 1.5% ZEO. Carvacrol and menthone were found to be the main compounds of ZEO and MEO following GC analysis, respectively. Atomic absorption spectrophotometer showed transfer only a minuscule amount of Zn2+ ions to the meat. Overally, the PLA/ZnO films containing the essential oils could be deemed as a potential alternative to the current common technologies for extending the shelf-life of meat products like Otolithes ruber fillets.