Quality improvement of rainbow trout fillets by whey protein isolate coatings containing electrospun poly(ε-caprolactone) nanofibers with Urtica dioica L. extract during storage

Novel bioactive coatings were prepared to extend the quality and shelf life of fresh fish fillets of rainbow trout (Oncorhynchus mykiss). For this, whey protein isolate (WPI) with 96 g/100 g protein content was used as the coating-forming agent with glycerol in a ratio of 3.3 g/100 mL as plasticizer. Poly(ε-caprolactone) (PCL) nanofibers containing extract of Urtica dioica L., often called stinging nettle, at 60:40 (g:g) were produced by electrospinning. These were then incorporated into WPI at different concentrations, i.e., 50 and 70 g/100 g. Fish fillets protected by means of the functionalized coatings were stored for 15 days at 4 °C. Protected fish fillets exhibited higher antimicrobial efficiency against mesophilic, psychrophilic, and lactic acid bacteria as well as Enterobacteriaceae than equivalent coatings containing Urtica dioica L. water extract. In particular, incorporation of 70 g/100 g PCL nanofibers exhibited the lowest counts in both bacterial growth and values in total volatile basic nitrogen (TVB-N) and thiobarbituric acid (TBA) during storage. Additionally, the coatings successfully provided antioxidant activity that could help to increase fish fillets' quality and favor their preservation.