1H NMR study of the changes in brine- and dry-salted sea bass lipids under thermo-oxidative conditions: Both salting methods reduce oxidative stability

Abstract

Farmed European sea bass (Dicentrarchus labrax) fillets were salted by two methods, brine- and dry-salting. Both salted and unsalted fillets were submitted to thermo-oxidative conditions in order to study the evolution of their lipids and their oxidative stability. Lipids were extracted and studied by proton nuclear magnetic resonance (1H NMR). This technique allowed the evolution of the molar percentages of the different kinds of acyl groups (omega-3, docosahexaenoic, eicosapentaenoic, diunsaturated omega-6, and omega-1) to be followed. In addition, the formation of secondary oxidation compounds, such as aldehydes (alkanals, trans-2-alkenals, trans,trans-2,4-alkadienals), could be monitored and quantified by means of this technique, providing information about the oxidative status of the sea bass fillets. No primary oxidation compounds were detected. Moreover, the concentrations of 1,2-diglycerides and phosphatidylcholine were determined. Equations for all the mentioned quantitative determinations were proposed. It was evidenced that the use of salting methods did not provoke the immediate oxidation of sea bass lipids, but reduced their oxidative stability, this effect being more pronounced in dry-salting. Although oxidation began earlier in brine-salted samples than it did in unsalted ones, these latter reached a degradation level of a similar order to that of the brine-salted samples after a certain period of time under the degradative conditions. Practical applications: The results of this study will be useful for optimizing the conditions of European sea bass salting processes, in order to minimize possible lipid oxidation. This is of great importance for sectors of the seafood industry, which focus on this and other fish species with similar lipid content and acyl group proportions, and which are interested in providing high quality food products. The information given by 1H NMR, a rapid and non-destructive method compared with other conventional chemical ones, is very valuable for other researchers who also study fish lipid oxidation processes.