Lipid Oxidation in Fish and Fish Products of Interest for European Aquaculture

This thesis is based on three main trials. The overall aim of the present PhD thesis was to investigate the effect of some infra vitam and post mortem factors on oxidative stability of fish muscle. Killing procedures, such as percussion, asphyxia in air, and asphyxia by carbon monoxide (CO) were tested. Moreover, the effect of the utilization of mechanical separation technique (MSM) on oxidative stability of fish muscle was also investigated. The first research was conducted in order to investigate the effect of slaughtering procedures on oxidative stress and oxidative stability of muscle of farmed rainbow trout (Oncorhynchuss mykiss). Specifically, asphyxia in air was utilized as stressful method whilst percussion as a no-stress one. Stress at slaughter was assessed both by nucleotides analysis of muscle and lipid mediators detection in fish plasma. Moreover, the overall aim was to verify if stress during slaughter is reflected by the presence of some oxidative biomarkers in plasma, and if such as stress may affect the oxidative stability of fish muscle during a long term frozen storage (-10 °C, 165 days). Results revealed that stress during slaughter can greatly influence oxidative stress and oxidative stability of rainbow trout fillets. In fact, asphyxia, which was the most stressful method, induced a higher production of some lipid mediators such as hydroperoxides and EPA-derived prostaglandins, such as 12-HpHEPE/15-HpHEPE and PGD3/PGE3. As a consequence, fillets derived from asphyxiated fish were less stable in terms of oxidative stability and showed lower shelf-life. In the second research, Atlantic salmon was utilized as target species in order to evaluate the effect of different stunning/killing procedures on lipid and cholesterol oxidation during 14 days of refrigerated storage. Carbon monoxide (CO) has been recently utilized as a new stunning/killing procedure for Atlantic salmon (Salmo salar), however no studies on its effect on fillets quality were previously performed. For this reason, lipid and cholesterol oxidation of fillets were evaluated at two times of refrigerated (2.5 °C) storage, T0 (64 h after death) and T14 (14 days from T0). The use of CO was compared with the percussion (P) method, considered as control. Results revealed that fatty acid profile, primary (conjugated dienes) and secondary (TBARS) oxidation products, cholesterol oxidation products (COPs) and carotenoids were unaffected by the killing method. Despite the low oxidative status of lipids (0.66 and 0.60 mg malondialdehyde kg-1 muscle in P and CO fish, respectively), cholesterol was found to be highly oxidized (0.17 and 0.13 mg COPs kg-1). Moreover, storage was found to significantly affect the oxidative stability of fish muscle by increasing oxidation products. Interestingly, TBARS content doubled while the increase for COPs was not homogeneous: α- and β-epoxycholesterol increased by 25%, whereas triol and 7-ketocholesterol increased by 48 and 62% respectively. In conclusion, the quality of salmon fillets just after slaughtering and after 14 days of refrigerated storage at 2.5 °C did not change, irrespective of the killing method adopted, suggesting that the CO method may be applied without any detrimental effect on the quality of fish fillets. Nevertheless, storage time was confirmed to be a critical phase in order to maintain unaltered fish fillets quality. In the third study instead, the effect of a post mortem factor such as mechanical separation process for obtaining “mechanically separated meat” (MSM) from decapitated and eviscerated fish was studied. Mechanically separated meat has been utilized in certain meat and meat products, especially from pork, beef and chicken. This process however, is not so applied in European fish industries. The overall aim of this third research was to evaluate the effect of that process on physical and chemical properties of three species farmed in the European aquaculture as well as European sea bass (Dicentrarchus labrax), gilthead sea bream (Sparus aurata), and rainbow trout (Oncorhynkus mykiss). Specifically, MSM-burgers were compared with minced-burgers and whole fillets by evaluating colour, dienes, TBARS, and fatty acid profiles during storage.