Effect of vacuum packaging and low-dose irradiation on the microbial, chemical and sensory characteristics of chub mackerel (Scomber japonicus).

The effects of vacuum packaging followed by gamma irradiation treatment (1.5 kGy) on the shelf-life of fillets of chub mackerel (Scomber japonicus) were examined, during chill storage. The control and the treated packs were analyzed periodically for chemical (TMA, TBARS, biogenic amines) and microbial characteristics. Based on chemical and microbial data, vacuum packaging - by itself - was improper in extending the shelf-life of chub mackerel, estimated to 7 days. On the 7th day, TMA and Histamine contents reached the defect action levels, associated with the presence of mesophiles (3.7 log UFC/g); total coliforms (3.5 log UFC/g); staphylococci (1.9 log UFC/g) and the emergence of Pseudomonas (1.7 log UFC/g), in both the control and the vacuum packaged lots. Combination of vacuum packaging and gamma-irradiation was found to delay the spoilage during 14 days of refrigerated storage, based on chemical and microbial analyses. Similarly, consumer hedonic tests were performed to determine the effect of different treatments on the taste of fish fillets. For all treatments, consumers failed to discriminate treated samples from the control, on the 2nd day of storage (p > 0.05). The acceptability test showed that low-dose irradiation (1.5 kGy) optimised the sensory quality, on the 3rd day of storage (p < 0.05). The employment of vacuum packaging combined to a low-dose gamma-irradiation (1.5 kGy) on chub mackerel is recommended to enhance microbiological quality (4 log reduction), alleviate chemical changes and extend the shelf-life by 7 days, leading to consumer appreciation of these products.

Seasonal change of lipid and fatty acid composition of little tuna Euthynnus alletteratus-by-products.

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.

Total lipids and fatty acids composition of the coastal and the deep-sea common octopus (Octopus vulgaris) populations: a comparative study.

The aim of this work was to investigate biochemical differences between Octopus vulgaris caught off costal zone and from the deep-sea of the Golf of Gabès (South coast of Tunisia). In both fishing grounds, octopus total lipids constituted almost 1.5% of wet tissue showing no significant difference (p < 0.05). The percentage distribution of fatty acids was not significantly different, neither between males and females, nor between both areas. Polyunsaturated fatty acids constituted about 50 % of the total fatty acids. Docosahexaenoic (DHA; C22:6 omega 3), eicosapentaenoic (EPA; C20:5 omega 3) and the arachidonic acids (C20:4) were the most important of this group with percentages of 25, 14 and 10% respectively. The saturated fraction constituted almost 30% of the total fatty acids. The most dominant saturated fatty acids were palmitic acid (C16:0) and stearic acid (C18:0), with 18% and 7% respectively. The monounsaturated content was found to contribute only 10% of the total fatty acids. Most of the monounsaturated fat was present as oleic acid (C18:1) and palmitoleic acid (C16:1) with 2.5% and 1.5% respectively. The presence of arachidonic acid in substantial proportions with an omega 3 to omega 6 ratios of 3.9 to 1 is of special interest because of the role of cephalopods in the traditional Mediterranean diet.