Summary:
Unstable conditions are commonly encountered during industrial storage and transportation of frozen fish. Temperature stress and fluctuations may increase the amount of unfrozen water in the muscle and enzymatic activity and lipid oxidation can thus still take place during frozen storage. The aim of this study was to investigate the changes of characteristics of different muscle types of herring at unstable modeled conditions during storage and transportation. Compositional changes, lipid oxidation and lipid hydrolysis were monitored in light and dark muscle of Atlantic herring (Clupea harengus), during frozen storage, as affected by temperature stress (samples were stored at - 25 ° C for 2 months, then stressed at - 12 ° C for 1 month, followed by storage at a stable - 25 ° C for the remaining storage duration ), and compared to samples stored at a stable - 25 ° C for 14 months. The dark muscle was more sensitive to lipid oxidation than the light muscle, leading to faster degradation. Increased lipid oxidation and lipid hydrolysis were observed in temperature-stressed samples of both muscle types. The study demonstrated the importance of avoiding temperature stress during industrial frozen storage and transportation to improve the quality and shelf life of frozen herring products. Removal of dark muscle by deep skinning could benefit both processors and customers regarding the shelf life and nutritional value of the light herring muscle.