Oxidative degradation and stabilization of Atlantic salmon (Salmon salar) by-products during storage

Cuenca Flores, Isabel (2022) Oxidative degradation and stabilization of Atlantic salmon (Salmon salar) by-products during storage. Masters thesis, Memorial University of Newfoundland.

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Abstract

Atlantic salmon (Salmo salar) by-products are sources of valuable bioactive compounds such as amino acids, peptides, enzymes, collagen, and omega-3 fatty acids. Due to high perishability, leading to spoilage and loss of quality, fish by-products end up in low value products such as pet food or fertilizer. Microbial spoilage, autolysis, and lipid oxidation are the main degradative processes that occur in fatty fish. In order to optimize their use in higher value products, the degradation occurring in the salmon by-products during storage should be controlled. Adequate processing before storage is required in order to avoid the degradation of the bioactive compounds present in the by-products. The main aim of the present study was to evaluate the effect of the presence of reactive organs (which could enhance lipid oxidation) and processing methods during storage for the stabilization of Atlantic salmon (Salmo salar) by-products against lipid oxidation and their subsequent utilization for the extraction of high-quality bioactive compounds. The present study investigated the effect of the presence of reactive organs including gills, heart, liver, bile sac, kidney, spleen, swim bladder, and gonads. In parallel, the effect of grinding and tumbling processing methods was investigated to stabilize and increase the storage time of by-products. The lowest lipid oxidation was obtained using tumbling in the absence of reactive organs. Tumbled by-products without reactive organs were stored at -18˚C, and the protecting effect of the addition of an antioxidant against lipid oxidation of by-products using tumbling and grinding. The fatty acid profile analysis was performed on the oil extracted from frozen samples, and the oxidation of the lipids was studied. A promoting effect of lipid oxidation was observed in the ground by-products, significantly affecting viscera's lipid oxidation and hydrolysis. Salmon heads, frames, and viscera without reactive organs were stable during storage regardless of added antioxidant or the processing method (except for ground viscera). The fatty acid analysis showed five primary fatty acids present in the polyunsaturated fraction of the oils from heads, frames, and viscera: linoleic acid, alpha-linolenic acid, docosahexaenoic acid, eicosapentaenoic acid, and docosapentaenoic acid. The PUFA content remained stable during storage at -18˚C in ground and tumbled by-products with and without addition of antioxidant. However, the amounts of EPA and DHA in the present study were lower (from 3.58 to 5.7 g/100 g) compared to similar studies performed in Atlantic salmon by-products probably due to lower quantities of EPA and DHA present in the fish diet. The lipid stability of by-products containing higher levels of EPA and DHA should be investigated.

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