Ultrastructural changes during frozen storage of cod (Gadus morhua L.)

Summary Myofibrillar proteins from post‐rigor unfrozen and stored frozen cod muscle have been studied by electron microscopy. Changes in extracted proteins and corresponding myofibril residues were followed by negative staining and ultrathin sectioning throughout a frozen storage period of 120 weeks. In myofibrillar extracts a decrease in the number of actomyosin filaments and an increase in the number and size of large aggregates was found. A decrease in the length and amount of attached myosin was noticed in actomyosin filaments. The changes observed were most extensive at — 10°C, less pronounced at — 20°C and hardly noticeable at — 30°C. According to the appearance of the myofibril residues thick myofilaments had been almost completely extracted from unfrozen muscle and were increasingly resistant towards extraction the higher the temperature during frozen storage.