SPONSORED BY ALLTECH

By SHEENA FAGAN

Selenium occurs in different chemical forms that determine its bioavailability, function and toxicology to human and animal health.

Selenized yeast, in which selenium is taken up by the yeast during a controlled fermentation process, is the most bioavailable organic selenium source. However, there are a number of companies around the world that produce organic selenium yeast products, with each manufacturer claiming superior performance for livestock. Yet the form and content of selenium in selenium-yeast supplements depends on the manufacturer, and variation in product quality may occur due to factors such as yeast strain, media composition and feed processing (Weekley and Harris, 2013).

Thus, as one begins to select a yeast product for dietary organic selenium supplementation for food-producing animals, it is important to know the availability of the selenium in that product.

Characterization and comparison of selenium-enriched yeast products has traditionally been made by quantifying total selenomethionine (SeMet) content, the major component of selenium-yeast. A disadvantage of this approach, however, is that it does not consider the effects of selenium deposition on subsequent digestive availability and instead assumes all selenium yeast products to have the same bioequivalency.

In a recently published article, researchers at Alltech used state-of-the-art methodologies to examine commercially available selenium-yeast products and determine the true incorporation of SeMet into yeast proteins (Fagan et al., 2015). Overall, the study indicated that significant differences exist between selenium yeast products in terms of selenium localized deposition into proteins. To further address the effects of subcellular compartmentalization of selenium, the scientists assessed the same products for potential bioavailability using an in vitro approach.

Selenium bioavailability is defined as the fraction of selenium that reaches the blood system from the gastrointestinal (GI) tract and is available to the organism’s metabolism. In other words, in order to exert a health benefit, the compound of interest needs to withstand feed processing, be released from the food matrix post-ingestion and be bio-accessible in the GI tract (Rein et al., 2013).

In vitro digestion models are widely used to study the structural changes, digestibility and release of food components under simulated gastrointestinal conditions. Our analysis demonstrated that while some products appears to contain a larger number of selenium-containing proteins, many of these survive in vitro digestion and so the incorporated selenomethionine/selenocysteine residues will be less bioavailable (Figure). Product 1 contains the lowest number of selenium-containing proteins following digestion and, furthermore, those detectable after digestion show a considerable decrease in abundance.

Sel-Plex represents the sample with the largest amount of selenium-containing protein digested and by inference, the largest bioavailability of selenomethionine/selenocysteine. As subcellular deposition of selenium within selenium-yeast is so widely different, it is reasonable to expect that these preparations will also differ in parameters such as shelf-life, bioavailability and indeed, toxicology. Rather than viewing these commercial products in exactly the same light, it is clear that they must be seen as very distinct preparations.

1. In vitro digestibility of Selenium yeast products.

References

Fagan, S., R. Owens, P. Ward, C. Connolly, S. Doyle and R. Murphy. 2015. Biochemical comparison of commercial selenium yeast preparations. Biol. Trace Elem. Res. 166(2):245-259.

Rein, M.J., M. Renouf, C. Cruz-Hernandez, L. Actis-Goretta, S.K. Thakkar and M. da Silva Pinto. 2013. Bioavailability of bioactive food compounds: A challenging journey to bioefficacy. Br. J. Clin. Pharmacol. 75(3):588-602.

Weekley, C.M., and H.H. Harris. 2013. Which form is that? The importance of selenium speciation and metabolism in the prevention and treatment of disease. Chem. Soc. Rev. 42(23):8870-8894.