Lipid composition of selected tissues and milk of phocid seals of eastern Canada

Durnford, Edward A. D. (1998) Lipid composition of selected tissues and milk of phocid seals of eastern Canada. Masters thesis, Memorial University of Newfoundland.

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Abstract

Marine oils and seafoods have received much attention since their consumption has been associated with beneficial cardiovascular effects. Much of the research, however, has focused on fish oils and oily fish with some recent reports on harp and grey seal blubber oils. This study investigated the lipid composition of several tissues from all six species of Eastern Canadian Phocid seals. The position of fatty acids of the triacylglycerol (TAG) backbone also has important dietary and biochemical implications. Therefore, the positional distribution of fatty acids of the TAG of harp seal milk was also investigated. -- Proximate composition of the samples indicated that blubber, followed by milk, had the highest lipid content and the lowest levels of moisture and protein. Muscle tissues had the highest protein content and milk had the lowest amount of ash. -- Thin layer chromatography-flame ionization detection (TLC-FID) studies indicated that lipid class composition was primarily dependent on the tissue as compared to species of seal. Furthermore, some tissues had a very unique composition. Blubber and milk lipids were found to be mainly composed of TAG while brain had undetectable levels of TAG. Brain lipids were high in cholesterol and cerebrosides, the latter being a polar lipid class not found in any other tissue examined. -- The fatty acids of all tissue lipids contained relatively high proportions of polyunsaturated fatty acids (PUFA) of the ω3 type (12- 23%) and these were composed of eicosapentaenoic acid (EPA, 0.3-13%), docosapentaenoic acid (DPA, 0-5%), and docosahexaenoic acid (DHA, 3-16%). Multivariate analysis showed that fatty acid composition varied more from tissue to tissue than species to species. Several unique features in the fatty acid compositions of various tissues were also identified. Blubber was found to be high in monounsaturated fatty acids (MUFA), but low in arachidonic acid and dimethyl acetals. Brain lipids, on the other hand, were high in dimethyl acetals. Brain lipids were also high in DHA. Lung tissue lipids were very high in saturated fatty acids, especially palmitic acid, and heart lipids had a higher content of linoleic acid than lipids of other tissues examined. -- Multivariate analysis also indicated clear differences in the neutral and polar lipid fractions of corresponding tissues. The polar lipid fraction tended to be higher in dimethyl acetals, saturated fatty acids and PUFA of the ω3 configuration. The neutral lipid fraction of corresponding tissues, however, tended to be richer in MUFA and PUFA of the ω3 configuration. -- The positional distribution of the fatty acids of the triacylglycerols of harp seal milk was very similar to that of harp seal blubber. The ω3 PUFA were concentrated in the sn-1 and sn-3 positions while the saturated fatty acids were preferentially esterified to the sn-2 position.

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