Investigation on the shelf life and quality changes of tilapia during storage , and it’s consumer acceptability

Abstract

In this study، effects of slow and quick freezing، different packaging methods on quality of red and black tilapia and consumer acceptability of tilapia were investigatied. For preparation the samples for inveatigation the effects of slow and quick freezing methods on quality of tilapia، fresh tilapia fillets were frozen by slow and quick frozen methods. Slow frozen samples were prepared by storing the packed fillets directly in the -18 C°. The sprila freezing tunle with -30C° was also used for preparation the quick frozen sample. 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. Scanning Electron Microscopy (SEM) was used for study on the effects of the frozen condition on the microstructure of the fillets. Results indicated that two different frozen methods had significantly different effects on the quality of the samples. Most of the proximate composition (protein، moistre and fat) reduced during the storage. Quick frozen samples had significantly (P<0.05) lower reduction than slow frozen samples. All of the chemical quality indexes (PV، TBA، and TVN) increased during the storage as compered to the fresh samples. In these paramethers، the slow freezing had higher changes than quick freezing metods (P<0.05). The microbial properties of the samples showed decrese during the storage. Lower amont of total cuont was observed at the end of the storage time in the quick frozen samples than slow frozen once (P<0.05). The large changes in the fatty acid profiles of the sample were fond in all samples. During the storage SFA and MUF of the samples increased however، the PUFA decresed. A lower change was obseved in the quick frozen samples than slow frozen samples (P<0.05). Drip loss was increased in both frozen samples during the storage period. The percentage of the drip in the slow frozen samples was significantly higer than quick frozen samples (P<0.05). SEM micrographs were also showed that the chnges in the microstructur of the samples was different in the slow and frozen samples. Slow freezing methods had higher damge in the microstructure of the sample then quick freezing mathods. Sensory evaluation of the samples indicated that a better acceptability in the quick frozen samples than slow frozen sample (P<0.05). For study the effect of some different methods of packaging fresh fillets were packed Modified Atmosphere Packaging (MAP) (40% CO2، 5% O2 and 55% N2) Vacuum Packaging and normal and stored in the refrigerator's. The packaged samples in these methods were examined for 10 days with regard to the changes in chemical (TVN، PV، pH)، microbial (total viable count) and organoleptic agents. The results indicated that the samples packed in MAP conditions had higher quality than that of the other methods at the end of the storing period. In addition، the slower destructive impacts and microbial growth was observed in MAP. According to the obtained results، we can suggest that the packaging of tilapia under MAP conditions resulted in the increase in the durability، storing، and distribution period of fillets. Consumer acceptability of tilapia was also investigated in this research. For this research، 300 farmed Nile tilapia (Oreochromis niloticus) and 300 Red tilapia (Oreochromi. niloticus × Tilapia mosambicus) were collected from the salt water fish research station located in Bafgh Yazd. The fish were transported to the National Fish Processing Research Center by using CSW method. Two methods were used for the study. First method was based on the sensory evaluation. In this method the fish fillets were cooked with Tuster and then the cooked sample were tested by 8 trained panelists. The second methods was established by Central Location Test ) CLT) In this method the fish fillet were fried in sun flower oil and tested by 276 consumers of three provinces ( Theran، Gillan and Mazanderan). 9-point scale (1 = very bad، 9 = very good) was applied for investigating the acceptability level of the samples. Evaluation questionnaires of consumers were designed based on the CLT method and after evaluating the reliability and validity of the questionnaires. The proximate compositions of the fillet were also determined. Results showed that the mean acceptance rates of both species of tilapia did not have significant differences in all three provinces. However، comparing the acceptance rates of black fillets in Tehran (7/05)، Guilan (6/24) and Mazandaran (6/56) and red fillets in Tehran (6/91)، Guilan (6/19) and Caspian (6/59) showed significant differences in both samples. Results showed that the tilapia meat had between 1.30 – 1.68% fat، 18.70-19.26 protein، 78-79% moisture and 1.34-1.8 % ash.