Abstract: In order to explore the pattern of changes in the quality of tilapia fillets during freeze-thaw cycles and to elucidate the underlying mechanism, fresh fillet samples weighing approximately (130 ± 10) g were repeatedly frozen at ?4, ?18 or ?30 ℃ and thawed for up to four times and analyzed at each cycle. The correlation between quality parameters and the fractal dimension of the microstructure was analyzed. The porous microstructure formed by ice crystals in frozen fillets was characterized based on the fractal dimension and the quality parameters were measured. The results showed that the fractal dimension decreased with increaing number of freeze-thaw cycles. After four freeze-thaw cycles at ?4, ?18 and ?30 ℃, the fractal dimension decreased from an initial value of 1.925 to 1.815, 1.843 and 1.853, respectively, accompanied by a decrease in the elasticity and hardness as well as total peak area and an increase in the conductivity, total volatile basic nitrogen (TVB-N) content and total color difference ΔE. Overall, these parameters showed less changes with the decrease in freezing temperature. In addition, significant correlations were found between the fractal dimension and these quality indicators (P < 0.05, P < 0.01). Therefore, the fractal dimension has proved to be a novel and feasible method for evaluating the quality of tilapia fillets during freeze-thaw cycles.

Key words: tilapia fillet; fractal dimension; microstructure; freeze-thaw cycle; quality change