In this study, quality of fresh, slow frozen and quick frozen tilapia fillets and itschanges during storage at -18C° were investigated. For preparation the samples,fresh tilapia fillets were frozen by slow and quick frozen methods. Slow frozensamples were prepared by storing the packed fillets directly in the -18 C°. Thesprila freezing tunle with -30C° was also used for preparation the quick frozensample. The quick frozen samples were then stored at -18C°for six months.Proximate composition, fatty acid profiles, TBA, PV, TVN, Total cuont, Drip loss,and sensory evaluation of the samples were determined in every month. ScanningElectron Microscopy (SEM) was used for study on the effects of the frozencondition on the microstructure of the fillets. Results indicated that two differentfrozen methods had significantly different effects on the quality of the fillets. Mostof the proximate composition (protein, moistre and fat) reduced during the storage.Quick frozen filets had significantly (P<0.05) lower reduction than slow frozensamples. All of the chemical quality indexes (PV, TBA, and TVN) increasedduring the storage as compered to the fresh samples. In these paramethers, the slowfreezing had higher changes than quick freezing metods (P<0.05). The microbialproperties of the samples showed decrese during the storage. Lower amont of totalcuont was observed at the end of the storage time in the quick frozen samples thanslow frozen once (P<0.05). The large changes in the fatty acid profiles of thesample were fond in all samples. During the storage SFA and MUF of the samplesincreased however, the PUFA decresed. A lower change was obseved in the quickfrozen samples than slow frozen samples (P<0.05). Drip loss was increased in bothfrozen samples during the storage period. The percentage of the drip in the slowfrozen samples was significantly higer than quick frozen samples (P<0.05). SEMmicrographs were also showed that the chnges in the microstructur of the sampleswas different in the slow and frozen samples. Slow freezing methods had higherdamge in the microstructure of the sample then quick freezing mathods. Sensoryevaluation of the samples indicated that a better acceptability in the quick frozensamples than slow frozen sample (P<0.05).

Advisors: Yazdan Moradi, Abbas Ali Motalebi Counsellors: Seyed Ebrahim Hosseini, Mehdi Soltani

PhD