Profil et métabolisme des acides gras dans les tissus de la perche comme Perca fluviatilis L

Abstract : Perca fluviatilis L. (Eurasian perch) is characterized by a low intramuscular amount of lipids (<2%) and a high poly-unsatured fatty acid (PUFA) content. Docosahexaenoic acid (DHA, 22:6n-3) is present in a high proportion (40% of total fatty acid). The aims of this work are twofold: first to analyse the factors that could influence the lipid metabolism of Perca fluviatilis L. and second to identify factors that could explain the elevated contents of DHA in this fish. Assumptions, which have been tested to explain the high concentration of DHA, are a selective incorporation of this fatty acid and the ability of this fish to transform 18:3n-3 present in the diet into higher PUFA n-3, EPA and DHA; typical capacity of freshwater fish (bioconversion assumption). Three experiments have been conducted to test these assumptions. First, we described lipid composition of the different tissues, which play a role in lipid metabolism, by distinguishing total, neutral and polar lipids. Second, we identified and classified the factors influencing the lipid content and fatty acid composition by using a multifactorial approach. Third, we analysed the effect of diet fatty acid composition on PUFA n-3 tissues composition, enzymatic activity and genes expression, which code for enzymes implicated in fatty acid bioconversion. As Perca fluviatilis L. genome is not sequenced for the moment, the first work was to construct experiments for dosing enzymatic activity and gene expression in this species. Concentration of DHA was elevated in all the tissues we analysed, showing the good nutritional quality of Perca fluviatilis L. In the fillet, lipid content was stable. PUFA content was high (40-60% of total fatty acid), with elevated contents in DHA (35-45% of total fatty acid), which was the main fatty acid of this tissue. Lipid content in the liver and the fat tissue was variable according to the type of food. Adipose tissue, that is the lipid storage tissue in this species, was composed of 85-90% of lipid, of which 30-50% are mono-unsatured fatty acids (MUFA), mainly 18:1n-9. Liver fatty acid composition presented characteristics in an intermediate position between fatty acid composition of the fillet and the adipose tissue, but DHA was still the most abundant fatty acid. Our results were in accordance with literature. They added informations on the distribution and the concentration in neutral and polar lipids (NL and PL) of the tissues we studied (fillet NL/PL=50/50; Liver: NL/PL=60/40; adipose tissue: NL/PL=90/10), and on their composition in fatty acid (polar lipids are mainly composed of PUFA whereas neutral lipids are richer in saturated fat acids). Our results showed that the profile in fat acid depended on the tissue and the type of lipids. Our assumption of the ability of Perca fluviatilis L. to transform PUFA was verified because we were able to detect delta 6 desaturase in the liver, intestine, and brain. Moreover, the activity of this enzyme was put in evidence in the liver. Our assumption of selective incorporation of some fatty acids was also verified, MUFA being preferentially absorbed in the adipose tissue and PUFA in the fillet and the liver. Regarding the effect of factors we studied, our results showed that a differential determinism existed according to the type of fatty acid. The nature of lipids contained in the diet was the most important factor. This factor could influence the profile of fatty acid in the tissues through a direct effect or in interaction with other factors. Although the diet is the main factor of variation, our results showed that under condition of limited growth and for a fish with a commercial size, a content of 3% of DHA and 2% of EPA in the diet was sufficient to obtain, in the fillet, a composition in fatty acids of good quality for consumers with a limited bioconversion of PUFA
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Magali Peter. Profil et métabolisme des acides gras dans les tissus de la perche comme Perca fluviatilis L. Sciences agricoles. Institut National Polytechnique de Lorraine, 2008. Français. ⟨NNT : 2008INPL025N⟩. ⟨tel-01753047⟩

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