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Analytical Chemistry Division (V)


Number: 2005-041-2-500

Title: Determination of selenomethionine in selenized yeast supplements

Task Group
Zoltan Mester

Members: Chunying Chen, Heidi Goenaga-Infante, Joanna Szpunar, and Wayne Wolf

To provide the analytical, nutrition- and health- science community with clear guidelines on the determination of selenomethionine (the most abundant Se species) in yeast and yeast-based products.

Consumption of Se enriched food and feed supplements has increased dramatically as a result of the numerous health benefits reported, including protection of cells against the effects of free radicals, the normal functioning of the immune system and thyroid gland as well as protection against various forms of cancers. Yeast based supplements have emerged as an acknowledged means of alleviating selenium nutrient deficiencies, but it is evident from earlier studies that they are inconsistent in their makeup relative to label indications. Production of yeast-supplements, both animal and human, is a rapidly growing industry. IUPAC had already addressed the methodology of selenium speciation in biological materials in a report (Pure Appl. Chem., Vol. 72, No. 3, pp. 447-461, 2000). The report had a decent impact on the research community having obtained over 60 citations (Source: ISI)

Since then the concerns have focused around the determination of selenomethionine (SeMet) which is the dominant Se species in yeast based Se supplements. It is easier bioavailable and less toxic than selenite. Significant efforts have been made in the development of analytical methods for the speciation of Se in yeast in five recent years. Extraction procedures used are of paramount importance for the accurate determination of SeMet in yeast or other solid samples. Numerous extraction techniques have been developed for the extraction of SeMet in yeast. Despite this recent round-robin exercises show huge discrepancies among the results obtained by different methods published in peer-review literature. As much as 10-fold difference in the measured amount of SeMet was observed which is an amazingly poor performance for the measurement of a nutritional supplement ingredient. There is still a lack of consensus regarding whether there are forms of selenium other than selenomethionine in yeast but any of the procedures accounted for more than 80% of selenomethionine so far. Consequently, the major 4 industrial companies producing selenized yeast boast their selenomethionine content as a proof of the quality of their yeast without that a consensus exists on the methodology used and the validity of the measurements supplied.

The purpose of this project is to examine critically the existing methodology published in peer reviewed journals, and issue recommendations on the determination of this extremely important nutritional supplement. The task group is composed of scientists having a considerable experience in the field and a record of collaborations with different industrial companies interested in this issue. The work is going to be carried out in close collaboration with the potential stakeholders: the four major companies on the market: Alltech, Lallemand, Lesaffre and PharmaNord.



Last Update: 6 June 2006

<project announcement published in Chem. Int. Sep-Oct 2006>

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