Effect of Different Freezing Processes on the Quality and Histological Changes of Red Tilapia (Oreochromis niloticus × Tilapia mosambicus)

Background and Objective: Tilapia fish has been a favorable food and has a long history of farming.The present study was designed to investigate the effects of freezing speed and time on the chemical quality indices as well as histological changes.Materials and Methods:The fillets were frozen and packaged using too slow and quick-freezing methods and stored at -18EC for 6 months.Then fillet changes including drip, total volatile basic nitrogen (TVB-N), peroxide value (PV), thiobarbituric acid value (TBA) were evaluated on a monthly basis.Finally, histological changes were studied every two months by a scanning electron microscope (SEM).Results: All studied qualities changed in the course of different months in both quick and slow-freezing methods, though changes were more noticeable in slowfreezing.Drip percentage (4.8-11.4),PV (0.02-0.93 mEq kgG 1 ), TBA (0.03-1.2 mEq kgG 1 ) and TVB-N (12.63-21.93mg/100 g) levels all showed greater variations with slow freezing.On the other hand, it detected less degradation in fillets by the freezing method.Conclusion: The changes in Drip, TVB-N, PV and TBA as well as histological were less dramatic in the samples treated by quick freezing, compared to those of slow-freezing samples.