Freshness assessment of turbot (Scophthalmus maximus) by Quality Index Method (QIM), biochemical, and proteomic methods

•Freshness of turbot was assessed by QIM, biochemical, and proteomic methods.•Abundance changes in protein spots of interest were correlated with freshness indices.•The shelf-life of turbot was determined as 15 days.•Seven proteins were identified as the potential freshness markers.

The freshness of turbot stored at 4 °C for 18 days was assessed using Quality Index Method (QIM), biochemical, and proteomic methods, respectively. Results showed that the developed QIM scheme for turbot consisted of eight parameters which gave a total of 20 demerit points. QI showed a linear relationship to storage time (QI = 1.175 × tdays - 0.395, R2 = 0.988), and the remaining storage time could be estimated with an accuracy of ±1 day. pH, K values, TVB-N, and TVC increased significantly with storage time, and the shelf-life of turbot was determined to have been 15 days. Seven protein spots of interest were screened form the post mortem muscle proteome during storage, and were identified as: phosphoglucomutase-1, pyruvate kinase, kinesin-1 heavy chain, Troponin T, desmin-like, and actin, respectively. They were considered as the potential freshness markers of turbot, since the abundance changes of those proteins were significantly correlated with QI, K value, TVB-N, and TVC, and associated with the loss of fish quality and freshness. The work could provide useful information enabling the development of new strategies for freshness evaluation based on protein markers.