关键词: 反复冻融；调味鱼；鱼肉品质；蛋白特性；超高压；滚揉

Abstract: In order to explore the effects of repeated freeze-thaw cycles on the quality and protein properties of seasoned split fish prepared by ultra-high pressure (UHP) or tumbling (TB) marination, after being quickly frozen at ?35 ℃, the two fish samples were stored at ?18 ℃ for 20 days and then thawed and the freeze-thaw process was repeated five times consecutively. Changes in total bacterial count (TBC), thiobarbituric acid reaction substances (TBARS) value, total volatile basic nitrogen (TVB-N) content and protein oxidation indexes (sulfhydryl group and disulfide bond contents) were determined as well as in protein composition analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The microstructure, functional groups and secondary structure of myofibrillar proteins were evaluated by scanning electron microscopy (SEM), ultraviolet (UV) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The results showed that TBC in both samples remained at low levels, TVB-N content and TBARS value in both samples increased but also remained at low levels with increasing number of freeze-thaw cycles. Moreover, the sulfhydryl group content of myofibrillar proteins decreased significantly (P < 0.05), while the disulfide bond content increased significantly (P < 0.05); the relative contents of α-helix and β-turn decreased, whereas the relative contents of β-sheet and random coil increased. The electrophoretic bands of myosin heavy chain and actin became thinner and lighter. SEM observation revealed that the surface of the samples became wrinkled and rough with cavity after repeated freeze-thaw cycles. The quality change of UHP samples was significantly lower than that of TB samples, indicating that the UHP marination could delay the quality changes of seasoned split fish during repeated freeze-thaw process.

Key words: repeated freeze-thaw; seasoned fish; fish quality; protein characteristics; ultra-high pressure; tumbling