Abstract
Nile tilapia (Oreochromis niloticus) was grown in Bangladesh with four different feeding treatments as part of a project that aims to produce fish in a cost-effective way for low-income consumers in developing countries. Fillet and head tissue was analysed because both tissues were destined for human consumption. Gas chromatography with mass spectrometry (GC/MS) analyses of transesterified fatty acid methyl ester extracts indicated the presence of ~ 50 fatty acids. Major fatty acids in fillet and head tissue were palmitic acid and oleic acid. Both linoleic acid and polyunsaturated fatty acids with three or more double bonds were presented in quantities > 10% of total fatty acids in fillet, but lower in head tissue. Erucic acid levels were below the newly proposed tolerable daily intake in the European Union, based on the consumption of 200 g fillet per day. Moreover, further analysis produced evidence for the presence of the dicarboxylic fatty acid azelaic acid (nonanedioic acid, Di9:0) in head tissue. To verify this uncommon finding, countercurrent chromatography was used to isolate Di9:0 and other dicarboxylic acids from a technical standard followed by its quantification. Di9:0 contributed to 0.4–1.3% of the fatty acid profile in head tissue, but was not detected in fillet. Fish fed with increasing quantities of flaxseed indicated that linoleic acid was the likely precursor of Di9:0 in the head tissue samples.
Highlights
Fish is a rich source of digestible proteins, omega-3 fatty acids and essential micronutrients
The remaining share of 26% originated from dienoic fatty acids (~ 13%, Fig. 1a) with main contributions of linoleic acid (18:2n-6; ~ 12%) and polyunsaturated fatty acids (PUFAs) with more than two double bonds (~ 14%), including 3.5% docosahexaenoic acid (DHA, 22:6n-3) (Fig. 1a; Table 2)
Di9:0 was not detected in tilapia fillet, which pointed rather to the formation of Di9:0 in head tissue a selective transfer and enrichment in this tissue could not be fully ruled out
Summary
Fish is a rich source of digestible proteins, omega-3 fatty acids and essential micronutrients. Various dietary recommendations suggest the regular intake of 1–2 servings of fish and seafood per week [1]. About 20 kg of fish per capita is annually consumed worldwide [2]. To satisfy this high marked demand, aquaculture has significantly increased since the 1970s [2]. After carp (Cyprinidae), the production of Nile tilapia (Oreochromis niloticus) (8.3% of total finfish production in 2018) established as second largest mass of farmed finfish in the last decade [2].
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