Preparation of new nanocomposite film for controlling Listeria monocytogenes and Staphylococcus aureus in raw rainbow trout fillet

Objective(s): This study was aimed to evaluate the effect of chitosan-zinc oxide (CH-ZnO) film containing pomegranate peel extract (PPE; 0.5, 1 and 1.5%) on survival of Listeria monocytogenes and Staphylococcus aureus in raw rainbow trout fillets during refrigerated storage for 12 days. Methods: Total polyphenolic contents of CH-ZnO films containing different concentrations of methanolic PPE were determined with Folin-Ciocalteu reagent. In order to enumerate the inoculated pathogenic bacteria in raw rainbow trout fillets, Palcam Listeria selective agar (L. monocytogenes, incubated at 30 °C for 48 h) and Baird Parker agar (S. aureus, incubated at 37 °C for 48 h) were used. Results: Total phenolic content of CH-ZnO enriched with PPE was recorded to be 72-139 mg gallic acid/g film. For un-treated samples, the initially recorded population of 5 log CFU/g of L. monocytogenes and S. aureus were reached 5.36 and 3.03 log CFU/g at the end of designated study period, respectively. There were significant differences between samples packed with CH-ZnO films enriched with different concentrations of PPE (0.5, 1 and 1.5%) and untreated ones (P 0.05). In both samples treated with 1 and 1.5% PPE, the final bacterial population were reached below 1 log CFU/g at the end of storage period. Conclusions: The results of the present study indicate a potential use of CH-ZnO film enriched with PPE as an effective type of antimicrobial packaging to inhibit the growth of L. monocytogenes and S. aureus in raw rainbow trout fillets.