Abstract: In this study, the upper dorsal muscle of turbot was investigated for changes in fat content, moisture loss rate, mass loss rate, relatively extraction rate of myofibrillar protein, microstructure, shear force, hardness, chewiness and color. Besides, we also examined changes in the relative molecular mass of myofibrillar proteins in the fish muscle and proteins in the fish juice, Ca2+Mg2+-ATPase activity and total thiol group content. Results indicated that the moisture loss rate and mass loss rate increased, while fat content decreased with increasing cooking time. The extraction rate of myofibrillar protein decreased significantly in the first 2 min of cooking and then dropped to less than 10% by 4 min. Ca2+Mg2+-ATPase activity dropped to the lowest level at 2 min. Total thiol group content first increased and then declined during the first 1 min, followed by a leveling off. During cooking, the microstructure of turbot cubes was damaged; meanwhile, shear force, hardness and chewiness decreased significantly (P < 0.05). The L* value increased significantly to a plateau after 4 min. Myofibrillar proteins with different molecular weights continuously leaked out from fish muscle tissues, resulting in higher protein content in the exudate. In conclusion, turbot cubes (1.5 cm × 1.5 cm × 1.0 cm) cooked by steaming for 4 min had good quality.

Key words: turbot, mass loss rate, microstructure, texture, protein