Effect of hot smoking on proximate, fatty acid and amino acid composition of the European eel (Anguilla anguilla)

Abstract

The effects of hot smoking on the proximate composition, amino acid profile, and fatty acid composition of European eel (Anguilla anguilla) were investigated. Hot smoking significantly reduced moisture content (from 65.67 to 56.78 g/100 g) while increasing protein (17.76 to 21.45 g/100 g), lipid (14.17 to 18.16 g/100 g), and ash (1.26 to 2.74 g/100 g) concentrations (p<0.05), consistent with a moisture-driven concentration effect amplified by mineral absorption during brining. Glutamic acid, leucine, and aspartic acid were the dominant amino acids in both groups. Total amino acid content increased significantly from 15.50 to 20.51 g/100 g following smoking (p<0.05), with essential amino acid scores exceeding FAO/WHO/UNU (2007) reference values for all quantified EAA in both raw and smoked samples. The TEAA/TAA ratio remained stable at approximately 52.5% across treatments, and the predicted protein efficiency ratio did not differ significantly between groups (p>0.05), confirming the preservation of relative protein quality following processing. Regarding fatty acid composition, oleic acid (C18:1n–9) and palmitic acid (C16:0) were the dominant fatty acids in both groups. Smoking caused a significant increase in total saturated fatty acids (SFA: 31.23 to 41.18%) and significant decreases in total monounsaturated (MUFA: 47.14 to 40.75%) and polyunsaturated fatty acid (PUFA: 21.62 to 18.04%) fractions (p<0.05). However, when expressed on a wet-weight basis (g/100 g), absolute EPA+DHA content was nutritionally equivalent between groups (raw: 1.24 vs. smoked: 1.29 g/100 g), reflecting the concentration effect of lipids following moisture loss. The omega 3/omega 6 (n‒3/n‒6) ratio was 3.19 in raw and 3.33 in smoked eel, with no significant difference between groups. These findings indicate that while hot smoking alters the relative fatty acid distribution, European eel retains its nutritional value as a high-quality protein and n–3 fatty acid source following processing.

Keywords

• European eel
• Hot smoking
• Proximate composition
• Amino acids
• Fatty acids
• Nutritional quality

Supporting Institution

The study was not supported by any institution.

Ethical Statement

The authors declare that formal consent is not required for this type of study.

References

1. Ackman, R. G. (1990). Seafood lipids and fatty acids. Food Reviews International, 6(4), 617–646. https://doi.org/10.1080/87559129009540896
2. Adeyeye, E. I. (2009). Amino acid composition of three species of Nigerian fish: Clarias anguillaris, Oreochromis niloticus and Cynoglossus senegalensis. Food Chemistry, 113(1), 43–46. https://doi.org/10.1016/j.foodchem.2008.07.007
3. Alsmeyer, R. H., Cunningham, A. E., & Happich, M. L. (1974). Equations to predict PER from amino acid analysis. Food Technology, 28(7), 34–40.
4. Altın, A., & Ayyıldız, H. (2024). Assessing the status and management of European eel, Anguilla anguilla (Linnaeus 1758) fisheries in Türkiye: Trends, challenges, and conservation strategies (2019–2023). Marine and Life Sciences, 6(2), 58–63. https://doi.org/10.51756/marlife.1540493
5. AOAC International. (2000). Official methods of analysis of AOAC International (17th ed., Vol. 2).
6. Badawy, A. A.-B., Morgan, C. J., & Turner, J. A. (2008). Application of the Phenomenex EZ:faast™ amino acid analysis kit for rapid gas-chromatographic determination of concentrations of plasma tryptophan and its brain uptake competitors. Amino Acids, 34(4), 587–596. https://doi.org/10.1007/s00726-007-0012-7
7. Bligh, E. G., & Dyer, W. J. (1959). A rapid method of total lipid extraction and purification. Canadian Journal of Biochemistry and Physiology, 37(8), 911–917. https://doi.org/10.1139/o59-099
8. Bote, A., Trigo, M., Martínez, S., & Aubourg, S. P. (2024). The presence of bioactive compounds in European eel (Anguilla anguilla) skin: A comparative study with edible tissue. Marine Drugs, 22(3), 105. https://www.mdpi.com/1660-3397/22/3/105

9. Can Tunçelli, İ., Özden, Ö., & Erkan, N. (2022). Seasonal differences in lipid and fatty acid composition of European eels (Anguilla anguilla, Linnaeus 1758) from Orontes River, Turkiye. Aquatic Sciences and Engineering, 37(3), 169–174. https://doi.org/10.26650/ASE202221110462
10. Chi, Z., Yan, K., Gao, L., Li, J., Wang, X., & Wang, L. (2008). Diversity of marine yeasts with high protein content and evaluation of their nutritive compositions. Journal of the Marine Biological Association of the United Kingdom, 88(7), 1347–1352. https://doi.org/10.1017/S0025315408001938
11. Cieślik, I., Migdał, W., Topolska, K., Mickowska, B., & Cieślik, E. (2018). Changes of amino acid and fatty acid profile in freshwater fish after smoking. Journal of Food Processing and Preservation, 42(1), e13357. https://doi.org/10.1111/jfpp.13357
12. Colakoglu, F., Ormanci, H., & Cakir, F. (2011). Effect of marination and smoking on lipid and fatty acid composition of thornback ray (Raja clavata) and spiny dogfish (Squalis acanthias). European Food Research and Technology, 232(6), 1069–1075. https://doi.org/10.1007/s00217-011-1477-x
13. El-Obeid, T., Yehia, H. M., Sakkas, H., Lambrianidi, L., Tsiraki, M. I., & Savvaidis, I. N. (2018). Shelf-life of smoked eel fillets treated with chitosan or thyme oil. International Journal of Biological Macromolecules, 114, 578–583. https://doi.org/10.1016/j.ijbiomac.2018.03.125
14. Ersoy, B. (2011). Effects of cooking methods on the proximate, mineral and fatty acid composition of European eel (Anguilla anguilla). International Journal of Food Science & Technology, 46(3), 522–527. https://doi.org/10.1111/j.1365-2621.2010.02546.x
15. European Commission, Directorate-General for Maritime Affairs and Fisheries, & European Market Observatory for Fisheries and Aquaculture. (2021). Smoked eel in the EU: Price structure in the supply chain—Focus on the Netherlands, Germany and Denmark. Publications Office of the European Union. https://doi.org/10.2771/2362
16. Gómez-Limia, L., Carballo, J., Rodríguez-González, M., & Martínez, S. (2022). Impact of the filling medium on the colour and sensory characteristics of canned European eels (Anguilla anguilla L.). Foods, 11(8), 1115. https://doi.org/10.3390/foods11081115
17. Gómez-Limia, L., Cobas, N., & Martínez, S. (2021). Proximate composition, fatty acid profile and total amino acid contents in samples of the European eel (Anguilla anguilla) of different weights. International Journal of Gastronomy and Food Science, 25, 100364. https://doi.org/10.1016/j.ijgfs.2021.100364
18. Gómez-Limia, L., Franco, I., Blanco, T., & Martínez, S. (2019). Changes in amino acids content in muscle of European eel (Anguilla anguilla) in relation to body size. International Journal of Nutrition and Food Engineering, 13(2), 38–41. https://doi.org/10.5281/zenodo.2576930
19. International Union of Pure and Applied Chemistry. (1979). Standard methods for the analysis of oils, fats and derivatives (C. Paquot, Ed.; 6th ed.). Pergamon Press.
20. Kale, A., Kale, E., Akdeniz, N., & Canoruc, N. (2006). Elevated amniotic fluid amino acid levels in fetuses with gastroschisis. Brazilian Journal of Medical and Biological Research, 39(8), 1021–1025. https://doi.org/10.1590/s0100-879x2006000800004
21. Łuczyńska, J., Nowosad, J., Łuczyński, M. J., & Kucharczyk, D. (2023). Evaluation of chemical elements, lipid profiles, nutritional indices and health risk assessment of European eel (Anguilla anguilla L.). International Journal of Environmental Research and Public Health, 20(3), 2257. https://doi.org/10.3390/ijerph20032257
22. Morzel, M., & Van De Vis, H. (2003). Effect of the slaughter method on the quality of raw and smoked eels (Anguilla anguilla L.). Aquaculture Research, 34(1), 1–11. https://doi.org/10.1046/j.1365-2109.2003.00754.x
23. Mozaffarian, D., & Rimm, E. B. (2006). Fish intake, contaminants, and human health: Evaluating the risks and the benefits. JAMA, 296(15), 1885–1899. https://doi.org/10.1001/jama.296.15.1885
24. Ormanci, H. B., & Colakoglu, F. A. (2015). Nutritional and sensory properties of salted fish product, lakerda. Cogent Food & Agriculture, 1(1), 1008348. https://doi.org/10.1080/23311932.2015.1008348
25. Özogul, Y., Özyurt, G., Özogul, F., Kuley, E., & Polat, A. (2005). Freshness assessment of European eel (Anguilla anguilla) by sensory, chemical and microbiological methods. Food Chemistry, 92(4), 745–751. https://doi.org/10.1016/j.foodchem.2004.08.035
26. Özogul, Y., Ucar, Y., Takadaş, F., Durmuş, M., Köşker, A. R., & Polat, A. (2018). Comparision of green and conventional extraction methods on lipid yield and fatty acid profiles of fish species. European Journal of Lipid Science and Technology, 120(12), 1800107. https://doi.org/10.1002/ejlt.201800107
27. Paul, A. A., & Southgate, D. A. T. (Eds.). (1978). McCance and Widdowson’s The composition of foods (4th rev. and extended ed., Medical Research Council Special Report Series No. 297). H.M. Stationery Office.
28. Sato, K., Ohashi, C., Ohtsuki, K., & Kawabata, M. (1991). Type V collagen in trout (Salmo gairdneri) muscle and its solubility change during chilled storage of muscle. Journal of Agricultural and Food Chemistry, 39(7), 1222–1225. https://doi.org/10.1021/jf00007a005
29. Sikorski, Z. E., & Kołakowska, A. (1994). Changes in proteins in frozen stored fish. In Z. E. Sikorski, B. S. Pan, & F. Shahidi (Eds.), Seafood proteins (pp. 99–112). Springer. https://doi.org/10.1007/978-1-4615-7828-4_8
30. Srivastava, A., Hamre, K., Stoss, J., Chakrabarti, R., & Tonheim, S. K. (2006). Protein content and amino acid composition of the live feed rotifer (Brachionus plicatilis): With emphasis on the water soluble fraction. Aquaculture, 254(1–4), 534–543. https://doi.org/10.1016/j.aquaculture.2005.11.014
31. Suryati, M. A., Azrina, A., Ismail, A., & Nor-Khaizura, M. A. R. (2022). Review on retention of long-chain omega-3 polyunsaturated fatty acids (EPA and DHA) in fish as affected by cooking methods. International Food Research Journal, 29(5), 975–990. https://doi.org/10.47836/ifrj.29.5.02
32. van Boekel, M. A. J. S. (2001). Kinetic aspects of the Maillard reaction: A critical review. Nahrung, 45(3), 150–159. https://doi.org/10.1002/1521-3803(20010601)45:3<150::AID-FOOD150>3.0.CO;2-9
33. World Health Organization, Food and Agriculture Organization of the United Nations, & United Nations University. (2007). Protein and amino acid requirements in human nutrition: Report of a joint WHO/FAO/UNU expert consultation (WHO Technical Report Series No. 935).