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Specification and bio availability of selenium from processed and tailor-made fishery products


The objectives of this project were:

- Speciation of selenium in fishery products by hyphenated analytical techniques in order to achieve a better understanding of the behaviour of selenium in fish as a nutritious food.
- Study the effect of various processing and farming methods on the speciation of selenium in fishery products in order to achieve an optimal tailor-made fishery product.
- To investigate the human bioavailability of selenium from a selected number of tailor-made fishery products in order to optimise the nutritional selenium status of the consumer.
The results show that selenium is present in a water-soluble protein fraction. In flatfish species the speciation of selenium seems to be different than in other fish species. Selenocompounds in flatfish are better soluble in water and occur mainly in low molecular weight fractions.
Farming trials with fish species like salmon, eel and catfish with selenium supplemented results in the incorporation of selenium in the various water soluble selenoprotein fractions. Selenium enrichment in farmed fish species like Atlantic salmon, cod, rainbow trout, eel and African catfish is possible by an appropriate selection of the selenium source in the feed. A linear increase in the selenium content in the muscle tissue of eel and African catfish was observed with the applied selenium concentration in the feed. Uptake of selenium by eel was lower than by catfish. Furthermore it was shown that the selenium content in African catfish was decreased after finishing the supplementation with selenomethionine due to growth related dilution of the internal selenium pool. A sevenfold increase in the selenium content of the muscle of African catfish could be obtained with selenomethionine in six weeks. Seleno-methionine and selenium enriched yeast are the best sources. The outcome of this part of the project shows the potential of farming selenium enriched tailor-made species as functional food.

The main aim of the bioavailability study was to assess the bioavailability of selenium from cooked and processed (salting) trout compared with the bioavailability of selenium from yeast by measuring the apparent absorption of selenium and estimation of the retention of the absorbed stable isotopes by measuring urinary excretion of selenium. For this purpose, two parallel studies were carried out in The Netherlands and the United Kingdom. The design is a parallel, randomised, reference substance controlled study in which six healthy men consumed 74Se biosynthetically labelled cooked trout, six men consumed 74Se biosynthetically raw salted trout and six men consumed 77Se biosynthetically labelled brewers yeast. Absorption was measured by faecal monitoring technique and the results were corrected for individual variation by expressing the absorption of the labelled food against the absorption of 82Se labelled sodium selenate drink in water. Calculation of the retention of the absorbed dose was based upon the measurements of the isotope label in the faeces and urine. Therefore hydride ICP-MS and GC-MS methods for the measurement of stable selenium isotope ratios in urine and faeces were developed and validated among the analytical centres involved in the project.

The outcome of these studies showed that fish is a good bioavailable selenium source. The bioavailability is not affected by the type of processing (cooked or salt treatment).
The mean absorption of selenium from fish (85-90%) compared well with the selenate absorption but is better than from yeast (50%). These results indicates also that selenium absorption from fish is as good as that from other foods of plant origin.

Linked to the human bioavailability research a study was carried out to evaluate if specific plasma selenoproteins can be used as markers of selenium status or selenium bioavailability in short term meal studies. Nearly all of the selenium present in animals, plants and micro-organisms is associated with proteins, several protein-bound forms have been identified. A large part of the total selenium in mammals is specifically incorporated into specific proteins with different biological functions. In human plasma, two selenoproteins have been identified so far: extracellular gluthatione peroxidase (eGSHPx) and selenoprotein P (SeP). For the first time it has been possible to study changes in plasma selenoprotein P levels in meal studies. No significant responses in extra cellular gluthatione peroxidase were observed indicating that selenoprotein P is the preferred biochemical marker for these types of studies. It was not possible to demonstrate significantly different effects on selenoprotein P concentrations related to test-meal composition.
Dissemination activities

* Plasma levels of selenium, selenoprotein P and glutathione peroxidase and their correlation to fish intake and serum levels of thyrotropin and thyroid hormones: A study on Latvian consumers. Hagmar, L, M. Persson-Moschos, B. Akesson and A. Schutz. European Journal of Clinical Nutrition 52(1998)796-800.

* Speciation and in vitro bioavailability of selenium in fishery products, L.H. Shen, M. Hoek-van Nieuwenhuizen and J.B. Luten. In "Seafood from producer to consumer, integrated approach to quality". Developments in Food Science 38. Eds: J.B. Luten, T. Borresen and J. Oehlenschlager. Elsevier, Amsterdam, 1998, 653-663.

* Speciation of selenium by FPLC-ICP-MS in seafood and farmed African catfish (Clarias goriepinus) with selenium enriched feed. Smink, N.V.H. M. Hoek-van Nieuwenhuizen and J.B. Luten. Proceedings 28th WEFTA meeting, October 4-7, 1998, TromsO, Norway.

* CE-ICP-MS publication: Design and characterisation of a microcentric nebuliser interface for capillary electrophoresis-inductively coupled plasma mass spectrometry. Tayler, K.A. Sharp, B.L. Lewis, D.J. Crews, H.M. JAAS., 1998, (13), 10, 1095.

* The use of HPLC-ICP-MS and CE-ICP-MS to investigate elemental speciation in human nutrition studies. D. John Lewis. Invited lecture presented at "Biological and Environmental Applications of ICP-MS", Robert Gordon University, June 24th 1998.

* The potential of Capillary Electrophoresis Coupled to ICP-MS. D. John Lewis, Karen A. Taylor, Helen M. Crews and Barry L. Sharp. Lecture presented at "5th International Symposium on Hyphenated Techniques in Chromatography and Hyphenated Chromatographic analysers", Bruges, February 11-13th 1998.

* Selenium against cancer, interview national Dutch journal Telegraaf and TV-broadcasting, February 1999

* The Development of an Interface for Coupling Capillary Electrophoresis and Inductively Coupled Plasma Mass Spectrometry and its Application to Elemental Speciation in Human Nutrition Studies. D. John Lewis, Karen A. Tayler, Barry L. Sharp and Helen M. Crews. Lecture presented at "5th International Symposium on Capillary Electrophoresis". York University, August 26-28th 1998.

* Fractionation of soluble selenium compounds from fish using Size-exclusion chromatography with on-line detection by inductively coupled plasma mass spectrometry. Lecture at TEMA 10 (Trace Elements in Man and Animals), Evian, France in May 1999, and at an Analytical Chemical Conference, Uppsala, Sweden in June 1999.

* Speciation of soluble selenium compounds form fish using size-exclusion chromatography with on-line detection by inductively coupled plasma spectrometry, Onning G. and Bergdahl, I.A. Analyst 1999; 124;1435-1439.

* Speciation of soluble selenium compounds from fish using size-exclusion chromatography with on-line detection by inductively coupled plasma spectrometry, Onning G. Lectures at TEMA 10, Evian, France, May 1999 and at Swedish Analytical Chemistry Conference, Uppsala, June 1999.

* Selenium speciation in yeast and dietary supplements. Winter Conference on Plasma Spectrochemistry, Crews, H.M. Fort Lauderdale, Florida, USA, January 10-15th January, 2000.

* The effect of selenium speciation on the bioavailability towards cultured fish. Kotterman, M.J.J. M. Hoek-van Nieuwenhuizen, J.B. Luten. Proceedings 30th WEFTA meeting, June 2000, Faroe Islands.

* Bioavailability of selenium from fish. Kotterman, M.J.J. M. Hoek-van Nieuwenhuizen, E. van den Heuvel. Proceedings 30th WEFTA meeting, June 2000, Faroe Islands.

* Interlaboratory trials on selenium stable isotope ratio analysis in biological material with hydride generation - Inductively Coupled Plasma Mass Spectrometry and GC-MS, J.B. Luten, P. Van Dael., M. Hoek-van Nieuwenhuizen, Th. Muijs, D.J. Lewis and H.M. Crews. Submission in 2000 to JAAS.

* Speciation of selenium by FPLC-ICP-MS in seafood. Kotterman, M.J.J. N.V.H. Smink, M. Hoek-van Nieuwenhuizen and J.B. Luten. Resubmitted for publication in Food Chemistry in 2000.

* Separation of soluble selenium compounds in different fish species. Onning G. Food Chem 1999; 68:133-139.

* Short-term changes of plasma selenoprotein levels after intake of defined fishmeals. Marie Persson, Gunilla Onning, Caroline Atherton, Tom Fox, Ellen van den
Heuvel, Mette Lorentzen, 7th International Symposium on Selenium in Biology and Medicine, Venice, 2000.

* Fisk ar en god selenkalla. Onning G & Persson M. Livsmedelsteknik 2000(42)6-7:42.
Fish is generally rich in selenium but is debated whether selenium from fish has the same bio availability to human beings as that from most other sources. Bioavailability is in turn associated with the question on the occurrence of different forms (speciation) of selenium in fish.

In this project various methods for the speciation of selenium have been developed and validated. Extraction procedures in combination with HPLC/FPLC for chromatographic separation coupled to ICP-MS or AAS for (on-line) detection of selenium have been applied to various fish species to study the selenium speciation.

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