The effect of slow and quick freezing on quality of Red Tilapia (Oreochromis niloticus × Tilapia mosambicus) fillets

The aim of this study was to investigate the effects of slow and quick freezing on proximate compositions, drip loss, sensory properties changes, and microstructure of Red Tilapia (Oreochromis niloticus × Tilapia mosambicus) fillets. For this reason, skinned and deboned tilapia fillets were frozen by slow and quick frozen methods. The samples were packed and storedat -18 °C for six months. Proximate composition, drip loss, and sensory evaluation of the samples were determined every month. Microstructure of the samples was studied using Scanning Electron Microscopy (SEM) every two months. Results indicated that fresh tilapia fillets had 1.68, 20.26, 1.38, 78.06 percentage of fat, protein, ash and moisture content, respectively. The proximate compositions were changed during the storageperiod. Quick frozen samples had significantly (P<0.05) lower changes than the slow frozen samples. The amount of moisture, ash, protein and fat for samples with slow freezing were 73.56, 2.76, 17.56 and 0.73 percentage and for samples with quick freezing were 76.31, 1.89, 18.01 and 1.18 percentage, respectively. The percentage of the drip in the slow frozen samples was significantly higher than quick frozen samples (P<0.05). The amount of drip was 11.4 and 6.1 percentage for slow and quick freezing samples after six month. SEM micrographs also showed that the changes in the microstructure of the samples were different in the slow and frozen samples. Slow freezing methods caused higher damage in the microstructure of the sample than quick freezing methods. Sensory evaluation of the samples indicated that there was a better acceptability in the quick frozen samples than slow frozen sample (P<0.05).