Scientific Alert Note

How to retain functional components during cooking of seafood

Heat treatment of fish muscle generally leads to losses of water soluble components, some of which may have beneficial health effects. As a part of the project 4.4 CONSUMERPRODUCTS, consequences of various household methods of preparing fish (baking, boiling and deep-frying) have been determined. Changes in the selected components selenium, n-3 polyunsaturated fatty acids and the free amino acids have been examined when cooking African catfish fillets. Main results show that selenium is retained well by all cooking methods, whereas losses were observed for the other components, but to a varying degree depending on the cooking method.




Sabine Mierke-Klemeyer and Jörg Oehlenschläger, FRCNF, Germany

Rune Larsen, Hanne Maehre and Edel Elvevoll, UiT, Norway

Narcisa Bandarra and Maria Leonor Nunes, IPIMAR, Portugal

Edward Schram, IMARES, The Netherlands



Fish contains many health beneficial components like vitamins, minerals and n-3 polyunsaturated fatty acids (PUFA). These components make fish a unique form of human nutrition. N-3 PUFA of marine origin has been associated with a reduced risk of developing coronary heart disease (CHD). Selenium is incorporated in enzymes to form selenoproteins which are involved in cell antioxidant systems. Other components like taurine, glycine and alanine are also shown to have health beneficial effects.


While cooking seafood products some water soluble components might leak out. This is not desired and therefore it has become of great interest to try and develop functional, tailor-made seafood products which could better retain the nutritional health benefits of the functional components during household preparation.  As part of the research, the content of the beneficial components in fillets of African catfish was compared before and after cooking, while also considering the weight loss occurring during processing.  In order to get comparable results, the retention of the beneficial components was calculated and documented according to Murphy et al. (1975).


The retention of selenium was 91 % for baking, 97 % for boiling and 104 % for deep-frying. According to the method of calculation it was concluded that no significant loss was found for selenium when comparing the household preparation procedures.


Losses of taurine, glycine and alanine during preparation were 25 – 40% for baking, 30 – 40% for boiling and 20 – 30% for deep-frying. Generally, there was no significant difference in retention of free amino acids between baking and boiling. However, deep frying resulted in significantly lower retention of taurine compared to baked samples. The fatty acid profiles were similar for baked and boiled fillets, but were significantly different from deep-fried seafood, due to absorption of saturated vegetable frying oil. Baking was the best preparation technique retaining more than 80 % of both the essential fatty acids EPA (20:5n-3) and DHA (22:6n-3), whereas boiling was only able to retain approximately 54% and deep-frying 56%.


In conclusion, there is no significant loss of selenium during various household preparations, thus making Se-enriched African catfish a good candidate for a tailor-made, functional seafood product which may contribute to consumer’s health and well being. For the other beneficial components investigated, further results are shown in the table below.


Retention of taurine, glycine, alanine and selenium before and after household preparation



Murphy EW, Criner PE, Gray BC (1975) J Agr Food Chem 23:1153-1157