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The main focus for this study was to compare and evaluate the quality changes and to determine the shelf life of frozen Scomberomorus commerson fillet using quick and slow freezing methods. Scomberomorus commerson fillets were frozen by slow and quick freezing methods and kept in the freezer at -18°C for 180 days. Then proximate analysis, chemical test (Total volatile base nitrogen; TVN, Thiobarbituric acid; TBA), drip loss, fatty acids profile and sensory analysis were assessed. Generally, Ash content, TBA, and TVN, drip loss, SFA values were significantly increased during storage time where as the moisture, protein, fat, PUFA and MUFA were significantly decreased (P<0.05). The ratio of TVN, TBA and drip loss was found to be higher in slowly as against quickly frozen fish. The PUFA (19.71), MUFA (23.40) and ω3 (14.69) of the quick samples was higher than that of the slow samples (16.99, 22.64, 12.34%, respectively). Regarding sensory analysis, both samples were in acceptable condition but the quality of quick samples was better than slow frozen samples. The quick freezing method was generally much more influent on quality parameters than slow freezing method.

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Changes in the fatty acid composition and biochemical indices of mackerel (which has a substantial lipid content) and shark (which has negligible lipid content) fillets stored at - 18°C for up to six months were measured. Lipid content was measured (6.35% and 1.38%) in mackerel and shark, respectively; however it decreased during frozen storage in both fish species. In analysis of fatty acids the amount of PUFA, especially
-3 ones, was more predominant in mackerel than shark, nevertheless, fatty acid composition has changed in both species during frozen storage. The amount of saturated fatty acids in contrast with unsaturated fatty acids increased due to oxidation of PUFA. The decrease in PUFA compounds (40.1% and 23.94%) was as follows:
-3 (48% and 42.83%),
-3/
-6 ratio (41.36% and 50%), PUFA/SFA ratio (56% and 42.23%) and EPA+DHA/C16 ratio (55.55% and 46.66%) in mackerel and shark, respectively. For both species, tiobarbituric acid (TBA), peroxide (PV), free fatty acids (FFA) and total volatile base nitrogen (TVB-N) values were significantly (P< 0.05) increased with storage time. The results showed that, among these indices, changes in the PV and TBA in mackerel were significantly (P< 0.05) larger than in shark; but changes of FFA and TVB-N in shark were significantly (P< 0.05) higher than in mackerel. It means that oxidative and hydrolytic deterioration are promoter factors of biochemical changes in mackerel and shark, respectively.

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Seafood contains compounds such as omega-3 fatty acids, fat-soluble vitamins, digestible proteins and micronutrients such as fluorine, calcium, iodine, copper, iron and zinc. Therefore, it is important to provide methods to increase the shelf life and also remove heavy metals from fish meat. In this study, using the biopolymers of chitosan (CS) and beta-cyclodextrin (β-CD), the oxidative stability of minced of commerson Scomberomorus fish during 12 days of refrigeration with chemical evaluations (acidity (pH), peroxide number (PV), and Thiobarbituric acid (TBA), water holding capacity (WHC)) and microbial (total microbial load count (TVC)) were studied. The ability of these two compounds to reduce the concentration of heavy metals during refrigeration was also investigated. According to the results, the use of CS and β-CD had a significant effect on the values ​​of all indicators compared to the control treatment (P <0.05). Therefore, it can be said that the use of CS and β-CD is effective in reducing the oxidation and growth of minced meat bacteria during storage in the refrigerator. The lowest pH value was observed in T8 and T11 treatments, the lowest PV value was observed in T8, T10 and T11 treatments, the lowest TBA value was observed in T7 treatment, the highest WHC value was observed in T8 treatment and the lowest TVC value was observed in T8 and T11 treatments. The use of CS and β-CD solutions also reduced the concentration of heavy metals in the minced meat of commerson Scomberomorus, so that T8 treatment showed the best performance in reducing cadmium, lead and mercury and against nickel removal, different treatments had almost the same performance.