Establishment of quality evaluation method for frozen tilapia ( Oreochromis niloticus ) fillets stored at different temperatures based on fractal dimension

To explore an effective quality evaluation system based on microstructure changes, tilapia samples were preserved at the temperature of −20, −40, and −80°C up to a storage period of 270 days. The porous structure of fish muscle was quantified using the cross-section area (CA) and fractal dimension (FD) of ice crystals, and the effectiveness of the two was compared. The relationships between microstructure changes and traditional quality parameters, including water-holding capacity, texture properties, K value, and total volatile basic nitrogen (TVB-N), were also explored. The results showed that FD dropped by 8.79, 4.53, and 3.03% of fillets at −20, −40, and −80°C after 270 days of storage, respectively. The better fitting on the basis of FD for evaluating quality of tilapia compared with CA. Traditional quality indicators were correlated well with the FD (R2 > 0.94), except for relaxation time (T2). The first-order kinetic equation FD = exp (0.0895 t exp[−7240.26/RT])/1.8903 was developed, and FD relative errors between predicted and observed values were all less than 3%, which demonstrated that the feasibleness and accuracy of quality evaluation based on FD during frozen storage. Practical applications Frozen storage inevitably has a negative impact on the tissue, water-holding capacity, and protein properties of fish. Thus, it is of great urgency to put forward an effective quality evaluation system of frozen fish. Here, tilapia samples were studied over a period of 270 days by measuring their microstructure of muscle fibers and traditional quality parameters. Correlation analysis of each index was also conducted and kinetic model based on FD was established and validated finally. In addition to establishing an effective quality evaluation system based on microstructure changes for tilapia, these results will provide new insights into the quality evaluation and laid a foundation for the application of fractal dimension in tilapia processing and transportation.