Application of the Mechanical Separation Process in Different Fish Species for the Development of a New Product Based on Fish

This PhD thesis is based on three main trials. The overall aim was to investigate the feasibility of using discard fish by adopting mechanical separation process to different fish species for creating new fish products (fish burgers). Different formulae of fish burgers were evaluated physically, chemically, nutritionally, and sensorily. The first research was conducted in order to investigate the impact of exploiting fish waste by mechanical separation process (MS) in order to produce ready-to-eat/cook foods based on fish. The aim was to evaluate the effect of MS process on physical and chemical characteristics, and on the nutritional value of the three farmed species: the European sea bass (Dicentrarchus labrax), gilthead sea bream (Sparus aurata), and rainbow trout (Oncorhynchus mykiss). Specifically, mechanically separated meat (MSM) burgers were compared with manual minced-burgers and whole fillets by evaluating yield, colour, pH, dienes, proximate composition, fatty acid profiles, and mineral composition. Results revealed that rainbow trout showed the highest yield for both manually and mechanically separated meat (53 and 50 g/100 g, respectively). The yield of MS process of sea bass and sea bream was higher than the manual operation yield (42 and 45 g/100 g, respectively against 39 and 40 g/100 g). The proximate composition, pH, colour, and mineral compositions are differently affected by MS process in the different fish species. However, MS slightly increased water content in sea bream and trout (71.12, and 70.65 g/100 g, respectively against 68.05, and 68.11 g/100 g of fillets) and decreased minerals, especially in trout, which showed loss of Ca, Mg, Na, and P. Interestingly, the fatty acid profiles of whole fillet, MS burger, and minced burger did not change. In conclusion, the MS process enabled manufacturing products with good characteristics in terms of yield and maintained nutritional value. In the second research, non-directly marketable specimens of European sea bass (Dicentrarchus labrax) and rainbow trout (Oncorhynchus mykiss) were used in order to produce healthy clean label products, and to examine the instrumental, chemical and sensory properties of raw and cooked fish burger recipes obtained from MSM characterized by differences in the recipe composition. Consumer attention towards healthy and more natural foods and producer attempts to reduce food loss have become more popular nowadays. For this reason, shear stress, proximate composition, fatty acid composition, and sensory characteristics of four formulations of fish burgers were examined. The four formulae differed in the ratios of European sea bass to rainbow trout (50:50 and 30:70) and the ratios of fish to potato flakes (dry matter ratio, DMR: 2.5:1 and 1.5:1). Results showed that the sensory attributes were affected mostly by the potato content of fish burger, whereas the effect of sea bass to trout ratio was negligible. The recipes with higher DMR were related to sandy, crusty, and dry 13 features, salty taste and the flavour of raw fish, while the lower DMR recipes were distinguished by soft texture, and a starchy flavour and a flavour of fish cooked in the oven. Moreover, shear stress was unaffected by the different ratios of fish or potato flakes in raw and cooked burgers. However, raw burgers with lower DMR had higher moisture and ash, and lower protein content, while cooked burgers with lower DMR had higher moisture and lower protein content. Interestingly, the fatty acid profiles of the four cooked burger recipes were not significantly different, and a quantity of 100 g of burger provided more than the recommended daily intake of the essential fatty acids. In brief, development of ready-to-cook products based on under-utilized fish through four clean label recipes of high nutritional value and good sensory attributes was attained, irrespective of prevalence of rainbow trout over the more expensive sea bass, or using higher ratio of potato flakes. In the third study instead, two mechanically separated meat from two fish species, the European sea bass (Dicentrarchus labrax), and rainbow trout (Oncorhynchus mykiss), were used for obtaining fish burgers submitted to a frozen storage. Recently ready-to-cook fish products, which are generally marketed as frozen and need some culinary preparation, stimulated the fish consumption. Therefore, the target of this research was to study the effect of two recipes, distinguished by the ratios of European sea bass to rainbow trout (50:50 and 30:70), and storage duration at sub-zero temperatures for obtaining convenient, easy-to-prepare, and good quality products. Particularly, the physical, chemical, and nutritional properties of raw and cooked fish burger of different formulations were assessed during storage. Results revealed that raw recipes with more trout have higher moisture, shear stress, yellowness, and intense colour. Conversely, they have lower values of primary (conjugated dienes) and secondary (TBARS) oxidation products. On the other hand, cooked recipes with more trout have more moisture, but lower protein content, and higher water holding capacity, yellowness, and intense colour. Furthermore, storage was found to significantly affect the shear stress, water-holding capacity and colour in raw and cooked fish burgers, causing their values to decline at the end of the storage. Excitingly, the nutritional value of raw and cooked fish burgers was decent and was not altered by the different formulae and storage durations. The highest oxidative stability was obtained in fish burger containing a high proportion of rainbow trout, which could be a matter of importance for the seafood industry because to the lower economical value of this species than sea bass.