Investigation of changes in the in vitro digestive properties of mirror carp (Cyprinus carpio L.) during postmortem storage based on protein degradation and oxidation

Dynamic changes in the in vitro digestive properties of postmortem mirror carp (Cyprinus carpio L.) at various intervals (0, 4, 24, 72, 120, and 168 h) under refrigerated conditions (4 °C) were evaluated based on protein degradation and oxidative reactions. Results indicated that protein degradation and oxidation intensified over storage time, as evidenced by increases in total viable counts, β-sheet content, and surface hydrophobicity, alongside decreases in α-helix content and fluorescence intensity (p < 0.05). The myofibril fragmentation index and TCA-soluble peptide levels peaked at 72.90 and 6.91 μmol tyrosine/g, respectively, whereas the total sulfhydryl content dropped to 50.25 μmol/g after 168 h postmortem. In vitro simulated gastrointestinal digestion experiments further demonstrated that aging enhanced protein digestibility. This study elucidates the postmortem dynamic patterns of freshwater fish, providing a theoretical basis for quality regulation.