Evaluation of the effects of frozen storage on the microstructure of tilapia (Perczformes: Cichlidae) through fractal dimension method

In this study, tilapia samples stored at -5 degrees C, -10 degrees C, and -15 degrees C for 64 days were investigated to establish effective quality evaluation methods based on microstructure changes during storage. The porous microstructure of the fish muscle in frozen storage was obtained in optical micrographs and quantified using fractal dimension method. The relationships were determined between fractal dimension and traditional freshness parameter, including electrical conductivity, water activity, and total volatile basic nitrogen. Moreover, variations in fractal dimension during storage were fitted by a first-order kinetics equation, and the shelf-life of tilapia was predicted through this equation. As a result, the fractal dimension was 1.9548 at initial time, and then it showed a decreased trend with the microstructure change in muscle tissue during storage. The correlations between fractal dimension and traditional freshness parameters were within +/-0.98, and the first-order kinetics equation of fractal dimension was obtained as d(t) = 1.9548 exp (1.00581 x 10(-4) t exp (-12.1657/T)). According to this equation, the prediction errors of tilapia shelf-life at different temperature were within +/-8.2%. The results indicate that fractal dimension can be used as a feasible approach to evaluate the freshness of tilapia in frozen storage. (C) 2015 Elsevier Ltd. All rights reserved.