Application of hurdle technology for the shelf life extension of European eel (Anguilla anguilla) fillets

Fresh fish, and especially fatty species, are highly perishable due to oxidative deterioration of fish flesh and the elevated microbial load on fish surface. The implementation of a variety of “mild hurdles” may significantly decrease the rates of fish chemical degradation and microbiological spoilage, by better retaining the initial quality, compared to more intense preservation techniques. The aim of this work is the comparative study of different, single or combined, treatments at 15 °C on the quality and shelf life of chilled eel fillets. Fish fillets were treated using osmotic solutions consisting of glycerol (30%–40%–45%) and 5% NaCl with and without former antioxidant impregnation by using Rosemary Serum. In all cases, water activity decreased to approximately 0.90 after 420 min of osmotic treatment. Untreated and osmotically treated fish fillets were subsequently stored at 4 °C and their stability under chill conditions was assessed based on microbial growth and oxidative deterioration. Microbial growth of treated samples was significantly delayed, especially due to the osmotic step (OS) and the derived water activity decrease. Lipid oxidation, a major cause of rejection for fatty fish such as eel, was greatly inhibited in treated fillets, owing to both ‘hurdles’, a_w lowering (OS) and antioxidant impregnation with rosemary serum (RS/OS), showing the synergistic effect of these successive procedures. Shelf life of treated eel fillets exhibited a more than 10-fold increase, as compared to the untreated samples, based on chemical composition and a 2 to 3-fold shelf life improvement, in terms of microbial growth.