In this study, we investigated the changes in the percentage of cooking loss, color, texture characteristics, sensory evaluation and microstructure of tilapia fillets under different boiling conditions. Meanwhile, the changes in myofibrillar protein content, total sulfhydryl content, Ca²⁺-ATPase activity and secondary structure were examined. The results showed that for each tested boiling temperature, the percentage of cooking loss increased to varying degrees with increasing heating time, and lower percentage of cooking loss was observed at 90 ℃ compared with the other boiling temperatures, the color parameters L* and b* increased and a* decreased compared with the fresh samples. The color of fillets remained better after undergoing high-temperature short-term boiling. The hardness, gumminess and chewiness gradually increased with increasing heating time at 50 ℃, but decreased at 60 ℃ and above. The texture properties of fish meat treated at 80 and 90 ℃ were relatively better. Scanning electron microscopy results showed that the structure of fish muscle tissue became looser after boiling, and gaps between muscle fiber bundles became observable. For each heating time, gaps between muscle fiber bundles gradually increased with increasing heating temperature, and the degree of damage became more serious. However, high-temperature short-term heating caused less damage to the structure of fish muscle tissue. The sensory evaluation resultswere basically consistent with the trends in all quality indicators. The myofibrillar protein content, total sulfhydryl content and Ca²⁺-ATPase activity decreased significantly (P < 0.05), and the degree of protein denaturation was smaller under the condition of low-temperature long-term heating. The proportion of α-helix and β-turn decreased, and the proportion of β-sheet and random coil increased. The proportion of α-helix and β-turn under the condition of low-temperature long-term heating were higher than under high-temperature short-term heating. In summary, considering the eating quality and actual production efficiency, high-temperature short-term heating is more suitable for tilapia fillets, and the quality of fillets boiled at 80–90 ℃ for 6–9 min is better.

In this study, the effects of different pretreatments (enzymatic treatment, freezing and soaking in ice-salt solution mixture) on the peeling of the Pacific white shrimp Penaeus vannamei and myofibrillar proteins in it were investigated. Shrimp peelability, the texture of peeled shrimps and the physicochemical and structural characteristics of myofibrillar proteins were analyzed after pretreatment. The results showed that compared with the two other pretreatments, enzymatic pretreatment for 3.5 h reduced the work required to peel shrimps and resulted in no significant difference in complete peeling rate (P > 0.05). The enzymatic treatment markedly decreased Ca²⁺-ATPase activity, the contents of total sulfhydryl and active sulfhydryl and intrinsic fluorescence intensity. The contents of total sulfhydryl and active sulfhydryl and intrinsic fluorescence intensity but not Ca²⁺-ATPase activity were decreased less by the enzymatic treatment than by freezing and ice-salt solution treatment. Enzymatically treated shrimps had no significant difference in surface hydrophobicity and protein carbonyl content compared with fresh and ice salt-treated samples, respectively (P > 0.05). Fourier transform infrared (FTIR)spectroscopic analysis showed that the contents of α-helix and β-turn in myofibrillar proteins were not significantly changed after pretreatment (P > 0.05), but the enzymatic and ice-salt treatments resulted in the transformation of β-sheet to random coil. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that freezing and ice-salt treatment changed the conformation but not the SDS-PAGE pattern of myofibrillar proteins. The enzymatic treatment caused the degradation of some macromolecular proteins, but did not cause a significant difference in the texture characteristics of shrimp meat compared with freezing and ice-salt treatment.

In this study, the effects of five common oxidative decontaminating agents (H₂O₂ solution, ClO₂ solution, NaClO solution, ozonated water and slightly acidic electrolytic water) on the bacterial decontamination of tilapia fillets and their influence on the texture, color and myofibrillar protein (MP) oxidation in tilapia fillets were investigated. The results showed that a decontamination rate of 80% was attained by immersion in 1 500 mg/L H₂O₂ solution for 8 min, 200 mg/L ClO₂ solution for 10 min, 200 mg/L NaClO solution for 10 min, 9 mg/L ozonated water for 10 min, or 30 mg/L slightly acidic electrolytic water for 20 min. Compared with the control group, treatment with decontaminating agents increased the hardness and L* value of tilapia fillets, decreased the a* value, MP content, total sulfhydryl group content, and raised the content of carbonyl groups and the amount of surface hydrophobic groups. The degree of protein denaturation in the slightly acidic electrolytic water and NaClO solution groups was the highest; the fluorescence intensity of MP was decreased after decontamination treatments, with the greatest decrease being found in the slightly acidic electrolytic water-treated group; the relative contents of α-helix and β-turn in MP were decreased, while the relative contents of β-fold and random coil were increased, with the most significant changes in the secondary structure of MP being observed in the slightly acidic electrolytic water-treated group (P < 0.05). MP underwent degradation to different extents, and the degradation degree of the slightly acidic electrolytic water group was higher than that of the other treatment groups. In summary, the oxidation of fish MP occurred to varying degrees after oxidative decontamination treatments, with slightly acidic electrolytic water treatment having the strongest oxidative effect.