Saloua Sadok

Enzymatic Hydrolysis of Shrimp Head Waste: Functional and Biochemical Properties

Shrimp head of Penaeus kerathurus obtained from industrial processing, were hydrolyzed by commercial trypsin (0.1%). Hydrolysis reaction was terminated by heat inactivation of the enzyme (95°C) followed by centrifugation. The produced protein hydrolysates were characterized by biochemical analysis for protein content, total free amino acids (FAA), total volatile basic nitrogen (TVB-N) and electrophoresis SDS-PAGE profile. Functional properties such as emulsifying capacity, fat adsorption and foaming property were assessed. Compared to the raw shrimp head protein, results from enzymatic hydrolysis showed a significant increase (p < 0.05) in protein content and FAA (17.22%). The low level of trypsin used in this study was sufficient to solubilize the substrate, resulting in substantial protein contents and TVB-N levels (< 6mg/100g), which was significantly lower than the acceptable limits established for marine 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 (SEA) 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 SEA 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; C22:6ω3), eicosapentaenoic (EPA; C20:5 ω3) 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.

Nutritional value of the Tunisian mussel Mytilus galloprovincialis with a special emphasis on lipid quality

This study reports, for the first time, data on nutritional quality parameters in Tunisian mussels, Mytilus galloprovincialis, with an especial emphasis on lipid compounds. Mussel condition index (CI), proximate composition and fatty acid profiles were investigated for a one year period in order to identify the best harvesting period. Analysis revealed that polyunsaturated fatty acids (PUFA) were the dominant fatty acids with a prevalence of n-3 over n-6 forms. Pearsons correlation indicated a strong relationship between CI and PUFA compound and Principal Components Analysis suggested that, from winter to summer, the product maintained a condition sufficiently good for marketing. The best CI and lipid quantity/quality occurred during summer and this may be used as criteria for product labelling. The study also included a thorough literature review that allowed data comparison on mussels from various Mediterranean sites and allowed the mussels from the Bizerte lagoon (North of Tunisia) to be differentiated.

Lipids and Fatty Acids Composition in the Tissues and By-Products of Two Tunisian Shrimp Species from the North and South Regions

Total lipid and fatty acid composition was determined in the muscle and by-products (heads, shells and tails) of Penaeus kerathurus and Metapenaeus monoceros caught off the North and South coasts of Tunisia. Shrimp total lipid levels in by-products ranged between 2 to 3.15% (p < 0.05) and were higher than fat tissue levels in both groups. No significant difference was found between tissue and by-product lipid contents of M.monoceros from both regions. However, significantly higher lipid content was found in P.kerathurus from the South than the North area. The percentage of polyunsaturated fatty acids were important in the tissues and by-products of both species from both regions. Thus, polyunsaturated fatty acids constitute the major fraction followed by saturated fatty acids and monounsaturated. The main fatty acids in both shrimp species muscle and by-products were C16:0, C20:5n–3, C22:6n-3, C18:ln–9, C18:0, C16:l, C20:4 and C18:ln–7.

TISSUE PARAMETERS OF THE SEA URCHIN (PARACENTROTUS LIVIDUS) : THE EFFECTS OF MAGNESIUM AND TRANSPORT STRESS

The present study investigates some biochemical and biological variables in sea urchins (Paracentrotus lividus) that were stressed in the course of collection, transportation and laboratory conditioning and the effect thereon of pre-treatment with a test compound; magnesium chloride (MgCl2). Handling and transportation for 5h resulted in significantly decreased gonadal indices due to unplanned spawning. The pre-treatment of sea urchins with 5 mmol l−1 MgCl2 reduced unplanned spawning during all of the experiments. Protein content and humidity were significantly higher (p < 0.05) in sea urchins treated with Mg than in the control group, these differences between groups were maintained throughout the experimental period. The analyses of gonad mineral compounds (Na+, K+, P, Ca2+ and Mg2+) showed a significantly higher (p < 0.05) Na+ and K+ tissue contents in the Mg-treated group than the control group throughout the conditioning period. Phosphorus with initial similar levels in both groups, however, showed a significantly higher gonad level (p < 0.05) in the Mg-treated group towards the end of the experiment (> 9 days).