This work investigated iron-catalyzed lipid oxidation in marine phospholipid liposomes. Oxygen consumption was used as a method to study lipid oxidation at pH 5.5 and 30 degrees C. The relationship between consumed oxygen and amount of peroxides (PV) and thiobarbituric reactive substances (TBARS) formed showed that both Fe2+ and Fe3+ catalyzed lipid oxidation. When Fe2+ was added to liposomes at a concentration of approximately 10 microM, an initial drop in dissolved oxygen (oxygen uptake rate >258 microM/min), followed by a slower linear oxygen uptake (oxygen uptake rate 4-6 microM/min), was observed. Addition of Fe3+ induced only the linear oxygen uptake. The initial fast drop in dissolved oxygen was due to oxidation of Fe2+ to Fe3+ by preexisting lipid peroxides (rate 79 microM Fe2+/min). Fe3+ is reduced by peroxides to Fe2+ at a slow rate (0.25 microM Fe3+/min at 30 degrees C) in a pseudo-first-order reaction. The redox cycling between Fe2+ and Fe3+ leads to an equilibrium between Fe2+ and Fe3+ resulting in a linear oxygen uptake. During the linear oxygen uptake, the interaction of Fe (3+) with lipid peroxide is the rate-limiting factor. Both alkoxy and peroxy radicals are formed by breakdown of peroxides by Fe2+ and Fe3+. These radicals react with fatty acids giving lipid radicals reacting with oxygen.

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Safe utilization of fish by-products is an important task due to increasing fish consumption. It can provide new valuable food/feed and will increase the economical profit and sustainability of the fishery industry. NMR spectroscopy is a reliable tool able to monitor qualitative and quantitative changes in by-products. In this work the trichloroacetic acid extracts of salmon backbones, heads and viscera stored at industrially relevant temperatures (4 and 10°C) were studied using NMR. Twenty-five metabolites were detected and the possibility of salmon by-products utilization as a source of anserine, phosphocreatine and taurine was discussed. Statistical data elaboration allowed determining the main processes occurring during by-products storage: formation of trimethylamine and biogenic amines, proteolysis and different types of fermentations. By-products freshness was evaluated using a multi-parameter approach: the trimethylamine and biogenic amines concentration changes were compared with Ki and H-values and safe temperatures and times for storage of salmon by-products were proposed.

This work examines how different factors such as temperature, amount of injected Fe 21, lipid concentration, pH, concentration of NaCl and concentration of dissolved oxygen influenced the lipid oxidation rate of liposomes made from cod phospholipids. The rate of lipid oxidation was measured by consumption of dissolved oxygen by liposomes in a closed vessel. The rate of oxygen consumption in liposomes was proportional to the concentration of iron and the lipid concentration in the assay mixture. The oxygen consumption rate was dependent on pH, with a maximum observed between pH 4 and 5. The addition of salt (final concentration 0.04-0.8 M) decreased the rate of oxygen consumption. The rate of oxidation was independent of the concentration of dissolved oxygen (in the range of 230-5 mM). The oxygen consumption rate followed Arrhenius kinetics, and the variation in activation energy found (60-87 kJ/ moles6K) might be due to variations in the composition of raw materials used in the experiments and different susceptibility to oxidation.

The antioxidant activity of three naturally occurring phenolic acids, caffeic (CaA), ferulic (FeA), and p-coumaric acid (CoA), and a synthetic compound, propyl gallate (PG), was evaluated in a food-related model system, a liposome dispersion of marine polyunsaturated fatty acids. Oxidation was induced by two different prooxidants, free iron ions and bovine hemoglobin (Hb). Continuous measurement of oxygen uptake was used to quantify the rate of lipid oxidation at steady state. Free iron-induced oxidation was reduced in the following order: PG > FeA > CoA. Caffeic acid worked as a prooxidant and increased the oxidation rate by a factor of 9. For Hb-induced oxidation, the relative efficiency was PG > CaA approximately FeA >> CoA. The antioxidant activity was also evaluated by four antioxidant capacity assays. In the Folin-Ciocalteu, ferric reducing/antioxidant power, and 2,2-diphenyl-1-picrylhydrazyl radical scavenging assays, the antioxidant activity followed the sequence PG > CaA > FeA > CoA. The order for the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) assay was found to be PG > CoA approximately FeA > CaA. The assays mainly reflected reducing abilities of the compounds. This work reports that in addition to the differences in the chemical structure of antioxidants, the antioxidant activity of phenolic compounds depends also upon the type of prooxidant.

Quality changes of vacuum packed Atlantic mackerel (Scomber scombrus) fillets during 12 months frozen storage at -27°C and 9 days chilled storage at +4 °C were evaluated. Freezing at -27 °C preserved the long chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs), vitamin D and the low molecular weight metabolites (LMW) (studied by high resolution nuclear magnetic resonance spectroscopy (HR NMR). Protein oxidation however took place, especially between 1-7 months, decreasing water holding capacity and protein extractability. During chilled storage, no lipid or protein oxidation was observed, but lipolysis increased, several LMW metabolites, relevant for sensory and nutritional quality degraded into non-favorable compounds. The content of biogenic amines was high at day 9 (e.g. 18 mg histamine/100g), jeopardizing safety. Preservation of mackerel fillets by freezing at -27°C is thus a better option compared to prolonged chilled storage at +4 °C; the quality was well preserved up till 12 months frozen storage.

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