This study evaluates the influence of various doses of gamma irradiation on some quality aspects of iced bonito (Sarda sarda). Fresh bonito sections were aerobically packed and gamma irradiated with doses of 0, 1.5, 3, 4.5, 6, and 7.5 kGy, samples were then chilled during 21 days. Microbiological analyses showed the presence of mesophilic and psychrophilic germs just before irradiation treatment. These germs were eliminated at doses !1.5 kGy. The analyses of total volatile basic nitrogen (TVB-N), trimethylamine (TMA) as well as the texture analysis showed that irradiated samples preserved a good quality during 21 days of chilled storage, whereas the control showed putrefaction. Histamine content was reduced after irradiation treatment, such decrease strongly correlated with the applied dose level. Fatty acid composition survey demonstrated that gamma irradiation associated with aerobic packaging influenced significantly the lipid profile. Irradiation at doses of 6 and 7.5 kGy reduced significantly poly-unsaturated fatty acid fraction. Results demonstrated that irradiation amplified the rate of lipid oxidation as shown by an increased peroxide value especially at higher doses. Gamma irradiation at low doses was effective in extending the bonito's shelf-life through the improvement of its microbiological, biochemical and textural qualities up to 21 days of chilled storage.
Little tuna (Euthynnus alletteratus) is an important Mediterranean commercial fish species. In this study, the lipids of tuna filet, head, viscera, liver, and gonads fished in Tunisian waters were examined in summer and winter. Total lipid content in most organs showed a significant variation due to seasonal change. The highest lipid content was found in head in little tuna fished in winter and summer (14.2%). The lowest levels were attributed to gonads (1.5%). The major fatty acids classes were polyunsaturated fatty acids (PUFA) followed by saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA). The lowest percentage of (MUFA) was recorded in winter season (9.77%). In summer, the proportion of PUFA decreased while that of SFA increased. The major contributing factor to the seasonal change of PUFA was n-3 fatty acids especially eicosapentaenoic acid (EPA) and docosahexaenoic (DHA). The lowest levels of PUFA/SFA were registered in summer. Little tuna by-products are an adequate raw material for fish oil production and excellent sources of n-3 fatty acids, the highest levels of PUFA were found during winter.
Changes in microbiological and biochemical quality of clams (Ruditapes decussatus) subjected to low doses of gamma irradiation (0.5 and 1 kGy) were investigated during alive storage, at 5°C. The mortality rate was significantly lower for irradiated clams compared with the control. In the same way, ammonia content was lower for irradiated clams (especially 1 kGy irradiated group). Considerable levels of total mesophiles, coliforms, staphylococcus, faecal streptococcus and Escherichia coli were detected in the control and irradiation had immediately reduced these charges; all bacteria studied experienced a 1-to 3-log reduction following 1 kGy irradiation. At the last day of storage, irradiated groups showed a noticeable reduction in the bacterial counts, whereas the mesophiles, staphylococcus and coliform germs were abundant in the control group (6.3, 2 and 1.7 log CFU g )1 , respectively). Irradiation doses up to 1 kGy had not an immediate effect on fatty acids composition (P > 0.05) and lipid profile was better in irradiated samples, where polyunsaturated fatty acid fraction was maintained throughout storage using irradiation. Also, sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed minor changes in proteins bands between different samples. These results demonstrated that 1 kGy irradiation appeared to be the optimum dose for treating alive clams (R. decussatus), through improving the microbial quality and alleviating biochemical changes during refrigerated storage.
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