Abstract: In order to explore the effect of freeze-thaw cycles on the quality of Scophthalmus maximus, the upper dorsal, lower dorsal, upper abdominal and lower abdominal muscles of the fish were monitored for changes in pH, thawing loss, cooking loss, shear force, texture properties and the types of water molecules after different freeze-thaw cycles. The results indicated that pH value first increased and then decreased during freeze-thaw cycles and the maximum value was observed after one cycle. As the number of freeze-thaw cycles increased, exudate loss during thawing and cooking and the contents of crude protein and polysaccharide in the exudates significantly increased (P < 0.05). After 5 freeze-thaw cycles, the upper dorsal and lower abdominal muscles showed the lowest and highest thawing loss of 18.54% and 23.85%, respectively, and the lower dorsal and upper abdominal muscles showed the lowest and highest cooking loss of 31.32% and 32.66%, respectively. In addition, the hardness, gumminess and chewiness gradually increased, the springiness declined, and the shear force dropped significantly (P < 0.05). T2 relaxation time revealed that all four muscles showed almost no change in bound water and a decrease in free water, with the greatest decrease (from 45.43 to 19.36) being observed for the upper dorsal muscle during freeze-thaw cycles. Therefore, freeze-thaw cycles significantly reduce the quality of Scophthalmus maximus, and this effect increases with increasing number of freeze-thaw cycles.

Key words: Scophthalmus maximus, freeze-thaw cycles, texture properties, relaxation time, quality