Effects of postmortem chilling times and subsequent frozen storage durations on microstructure and protein properties of tilapia (Oreochromis niloticus) fillets

This study aimed to investigate the effects of postmortem chilling times (4 °C: 0, 2, 8, and 12 h) and subsequent frozen storage durations (-20 °C: 0, 1, 2, and 3 months) on the microstructure and protein properties of tilapia fillets. Tilapia fillets with 8 h of chilling (P8) resulted in highest overall acceptability, hardness, chewiness, and shear force. The thawing losses of tilapia fillets with different postmortem chilling times for the same frozen storage duration were ranked as follows: P12 > P0/P2 > P8. With the prolongation of postmortem chilling times and frozen storage periods, the muscle tissue structure was gradually damaged, with the most severe disruption after 12 h of postmortem chilling time. Tilapia fillets pre-chilled for 8 h showed a 17.63% decrease in Ca²⁺-ATPase activity at 3 months of frozen duration, which was the smallest decrease compared with the other groups. Furthermore, the endogenous fluorescence intensity of P0, P2, P8 and P12 samples decreased by 34.53%, 14.29%, 13.95% and 26.98%, respectively, at the end of frozen storage. Overall, frozen storage durations had a greater effect on the quality of tilapia fillets than postmortem chilling times. In summary, the maximum postmortem chilling time for frozen tilapia fillets is recommended to be 8 h, with significant quality differences when frozen for more than 2 months.