EFFECTS OF PRESSURE PROCESSING ON FROZEN STORED MUSCLE PROTEINS OF ATLANTIC COD (Gadus morhua) FILLETS

This study reports on the protein changes that occur during the storage of frozen cod fillet portions and the relationship of these quality indicators to tex-tural changes in the pressed fish product. Changes in texture and ultrastructure were monitored by determination of moisture, evaporative loss, drip loss, total water loss on cooking and Instron shear force and peak slope measurements on raw and cooked products. Concomitantly, the chemical quality indicators of trimethylamine nitrogen (TMA-N), dimethylamine nitrogen (DMA-N), for maldehyde (HCHO), ammonia (NH3-N) and free radical content were analyzed to provide information on deteriorative storage changes in the products. Possible alterations in the myofibrillar proteins were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). High performance liquid chromatography (HPLC) was employed to study the pressure and storage temperature effects on the water soluble sarcoplasmic proteins (SAR). The ultrastructure of the fresh fillets, the pressed triangular and the unpressed fillet block portions were examined by phase contrast light microscopy and scanning electron microscopy. Significant loss (p 0.05) in moisture content and increased toughness was seen in the pressed −12°C versus the pressed −30°C cod fillets. This was also reflected in the significantly higher (p 0.05) concentrations of DMA-N, HCHO, NH3-N and free radicals. Results of the SDS-PAGE on the myofibrillar protein extracts showed the disappearance of the ca. 78,500