The a mberjack (S eriola dumerili ) is an important commercial fish species in Europe. The farming of the amberjack has attracted great interest in the Mediterranean region and is now considered one of the most important species for the diversification of commercial fish production in Mediterranean countries (Corriero et al., 2021) . In the fish processing sector, the further utilization of side streams and waste left after industrial production can contribute to the sustainability of raw materials, access to added value and higher profitability, and environmental protection by reducing the amount of by-products (Šilovs , 2018). Although fish by-products have a high potential for reuse and recycling, they are not yet sufficiently recovered to obtain high value-added products (Galanakis et al., 2015) . In addition, fish by-products are an excellent source of bioactive compounds such as amino acids, proteins, peptides, enzymes, gelatin, collagen, long-chain omega-3 polyunsaturated fatty acids, chitin, and vitamins (Vázquez et al., 2019) which can be used both as raw materials and as functional ingredients for the production of value-added products ( Suresh et al., 2018) . The d emand in the global market is shifting toward higher value-added processed seafood that features convenience, ease of preparation, and high nutritional value, and that can also satisfy the sensory-hedonic aspect . Fish protein hydrolysates (FPH) have great potential for use in food formulations because they possess several functional properties, including solubility, water-holding capacity, emulsifying , and foam-forming ability (Kristinsson and Rasco, 2000) . Processing can strongly influence the nutritional value of fish products, with fatty acids being the most vulnerable nutrients from fish , as they can easily be subjected to oxidation reactions resulting in quality degradation . For the development of added value, ready -to-cook fish products , it is therefore important to evaluate modifications possibly occurring during processing and storage, and to carefully check whether innovative processing affects the quality and nutritional value of the final product. The aim of the present study was to evaluate the effect of the addition of a protein hydrolysate from fish side streams on the quality and stability of fish balls made from mechanically separated amberjack meat during cold storage.
Materials and methods
In this study, the minced meat of amberjack was obtained by mechanical separation from the by-products of fish filleting. F ish balls were prepared with amberjack meat and fish protein hydrolysate (FPH) was added to the base formulation at a concentration of 1.5% by replacing the same amount of amberjack meat ; all other ingredients remained the same . The conventional product (control) was prepared using the basic formulation without fish protein hydrolysate. The fish balls were packed in polypropylene trays (PP) sealed with a high barrier film and packed in a modified atmosphere (MA) with a gas mixture of 80% N2 and 20% CO2. After packaging , the control and the innovative products were stored at 4°C for a total of 20 days. A nalytical determinations were carried out on the two groups of samples, the conventional product (control) and the innovative product, by taking samples for physicochemical analysis and microbiological analysis during storage . Experimental data were subjected to one-way analysis of variance (ANOVA) to determine the significant differences between samples. Tukey HSD (Honestly Significant Difference) multiple range test, with a significance level of p < 0.05 was applied.
The results of this study showed that t he presence of protein hydrolysate in fish balls significantly improved the microbiological shelf-life of the product (less than 12 days instead of less than 8 days). Moreover, the FPH delayed the accumulation of histamine by keeping its concentration below the EU limits throughout the shelf-life (12 days), contraril y to the conventional product where the limit was already exceeded after 8 days. During the shelf life, the innovative fish balls showed lower water activity than the conventional fish balls until the 12th day of storage (Fig. 1); this may have contributed to improved microbiological stability of the samples. Lightness (L*) was lower in the innovative samples than in the conventional samples, but during the storage period, L* values decreased in the conventional samples, while they remained almost constant in the innovative samples (Fig.1). The addition of 1.5% of protein hydrolysate showed no effect in counteracting the phenomenon of lipid oxidation in the fish balls. The amberjack fish balls produced in this study can be considered as an interesting new fish product obtained through amberjack by-product (fish components remaining after filleting) valorization. At the same time, to extend fish balls shelf-life and make them safer, more stringent handling procedures must be implemented during by-products production since the starting material presented a high microbial load.
This research was conducted under the NewTechAqua project supported by the European Union’s Horizon 2020 Programme (grant agreement No 862658). The project aims to expand and diversify European aquaculture production by developing and validating technologically advanced, resilient, and sustainable applications for finfish, molluscs, and microalgae.
Corriero, A., Wylie, M. J., Nyuji, M., Zupa, R., & Mylonas, C. C. (2021). Reproduction of greater amberjack (Seriola dumerili) and other members of the family Carangidae. Reviews in Aquaculture, 13(4), 1781-1815.
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