The holistic utilization of European plaice (Pleuronectes platessa) A study on chemical, nutritional and physicochemical quality

Abstract

European plaice (Pleuronectes platessa) is a distinctive marine flatfish species recognized for its morphology and asymmetrical body shape. This species inhabits the European coastlines, including the Norwegian Sea and shares the largest stocks and fisheries around the Northern Sea. Due to rising water temperatures, it is predicted that European plaice will migrate further north within the next decades, making the Norwegian coastline an attractive habitat area. While it is a highly appreciated fish species among customers in Europe, European plaice remains underutilized in the Norwegian market, presenting an unused potential. The present thesis investigated the quality and potential for the holistic utilization of European plaice, including fillets as the primary product and its by-product fractions. The primary focus lied on the chemical, nutritional, and physicochemical quality of fillets, including factors affecting these attributes. This involved the investigation of fish caught during different seasons, the assessment of chemical contaminants, and the storage stability during different storage conditions. Moreover, the nutritional profile of European plaice was studied and compared to other demersal fish species inhabiting the same area to evaluate the potential as a nutritional food source. Additionally, potential risks and benefits associated with increased consumption of European plaice fillets were evaluated and compared to other demersal fish species. The by-product fractions skins, backbones, and heads were characterized, and their potential for up-cycling into collagen was assessed using ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE), combined with enzymatic hydrolysis or salt-washing as pre-treatments. Furthermore, the feasibility of European plaice in aquaculture was explored, considering the chemical, nutritional, and physicochemical quality parameters from both female and male individuals. The results revealed that European plaice presents an excellent nutritional value, with good overall fillet quality in September and December. Moreover, it was observed that European plaice is a valuable source of beneficial compounds such as long-chain polyunsaturated fatty acids (LC-PUFA) as well as essential amino acids (EAA). Hereby meeting daily intake recommendations for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), considering the consumption of a 200 g portion. Fish caught in April showed lower physicochemical and chemical quality attributes, increased ATP metabolites as well as an accumulation of biogenic amines linked to microbial growth, indicating reduced overall quality during this period. Modified-atmosphere packaging (MAP) was found an ideal convenient packaging solution for retail to maintain high product quality during storage, next to whole fish sold on ice. Investigations of the by-product fractions of European plaice highlighted the potential for holistic utilization. Extraction of collagen was found particularly efficient for skins, independent of extraction method and pre-treatment, and yielded the highest collagen contents. Considering the comparison of farmed European plaice to wild stocks, the quality was found to be comparably high, suggesting its suitability for aquaculture. With this PhD study, a significant contribution to generating knowledge and uncovering the existing potential for increased holistic utilization of a fish species found along the Norwegian coastline was made. Hereby highlighting that European plaice is a nutritional food resource. Its beneficial nutritional composition and low potential risks of toxins as well as the possibility to sell in convenient packaging, make it a safe and appealing choice for consumers. Moreover, the utilization of green extraction methods to up-cycle by-products contributes to the green shift within the food and biotechnology industry.