Oxidation in fish muscle - The role of phospholipids, proteins, antioxidants and the effect of boiling on oxidation in fish muscle
The aim of the project was to increase the understanding of the effects of oxidation in fish muscles, which reduces the taste and nutritional value of fish. The effects of added natural antioxidants or antioxidants were assessed to improve the stability of fish products and thus increase the possibility of using fish in prepared dishes. A phospholipid model from cod was used to examine the effects of stimulants (hemoglobin from cod and char) and inhibitors in the liquid phase from capelin and Icelandic algae. The effect of boiling and added anti-corrosion substances on the taste properties and the formation of a so-called heating taste in boiled fish mince was also examined. The effect of oxidation on membrane phospholipids and proteins in the fish muscle model and in the fish mince during heating and storage was measured by sensory evaluation, color measurements, conventional evolution measurements (TBA), gas spectrometry measurements to identify volatile odorants and electrophoresis capillary capillary peptile and amino acids that affect taste and bioactivity. The relationship between these factors was examined to explain and better understand the oxidation process in fish muscles and the factors that limit the shelf life of prepared fish products. The main negative effects of oxidation on fish quality were the formation of odorants, mainly aldehydes, which are fatty acid degradants. Membrane fat in lean fish can therefore have a significant effect on the taste quality of prepared foods, despite being in small quantities. Oxidative stimuli such as blood in the flesh and boiling led to faster oxidation, which shows that with proper bleeding and mild heat treatment, oxidation could be limited and the taste quality of fish could be better maintained. In addition, oxidation can be reduced through the use of antioxidants. Measurements of the antioxidant activity of capelin broth in a fish muscle model showed that variable external factors such as seasonal fluctuations and the treatment of capelin raw material can affect the antioxidant activity. A novelty in this project is a basic study of the effects of capillaries and algae, as well as changes in the decomposition products during welding, which have a direct effect on the taste quality of the product. Research in this area is being continued in new projects that focus on better looking at natural antioxidants from capelin and algae, as well as their health-promoting effects.
The aim of the project was to study the effect of heating on oxidation of phospholipids, and the role of antioxidants in fish muscle to influence sensory quality and nutritional value. A phospholipid model from cod was used to study the effect of pro-oxidants (hemoglobin from cod and trout) and antioxidants in aqueous fraction of capelin and in seaweed extracts. The effect of heating and the addition of antioxidants on the sensory quality and the development of warmed-over-flavor (WOF) in fish mince were also studied. The development of degradation compounds in washed cod model system during storage and heating was studied by sensory analysis, color measurements, traditional lipid oxidation analysis (TBA) and gas chromatography analysis to identify volatile compounds. Capillary electrophoresis (CE) was applied for the analysis of peptides and amino acids that influence the sensory quality and bioactivity. The correlation between these analyzes was studied to better understand the oxidation processes in fish muscle and to explain factors reducing the shelf life of ready-to-eat fish products. Quality defects related to oxidation of polyunsaturated fatty acids and formation of volatile compounds like aldehydes contributing to rancidity and color changes were enhanced by pro-oxidative effects of blood and cooking. Membrane bound phospholipids are therefore of concern as precursors for off flavor and quality defects in lean fish despite of low fat content. Capelin broth appeared to have antioxidant effects in fish model system whereas press juice from whole capelin exhibited pro-oxidant effects. The outcome of this project is increased knowledge on oxidation in fish muscle to underpin the development of healthy and tasteful fish products of high sensory quality and nutritional values fulfilling the needs of consumers. Continued studies have been established in new projects to further characterize the antioxidant properties and possible health effects of capelin and seaweed extracts.