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United States Department of Agriculture

Agricultural Research Service

Title: Selenomethionine Content of Candidate Reference Materials

Authors
item Wolf, Wayne
item Zainal, Hanaa - SELF EMPLOYEE
item Yager, Brian - STUDENT, FCL

Submitted to: Fresenius Journal of Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 2001
Publication Date: March 15, 2001
Citation: Wolf, W.R., Zainal, H., Yager, B. 2001. Selenomethionine content of candidate reference materials. Fresenius Journal of Analytical Chemistry. 370:286-290.

Interpretive Summary: Selenium is an antioxidant of importance in the diet, often occurring as the organic form of selenomethionine (Semet, bound to protein. We have developed a procedure for determining Semet in foods such as wheat (a good source of dietary Se) and its protein fraction, gluten. This method is based upon the reaction of CNBr to cleave the CH3Se-functional group and form the volatile compound, CH3SeCN. Addition of isotopically enriched 74Semet to an analytical sample, allows a determination of the naturally occurring protein bound 80 Semet by GC/IDMS without a protein digestion step. For this method to be widely useful, appropriate reference materials (RM) must be available. We have examined several candidates. Wheat Gluten (NIST RM 8418) contains 40-60% of its assigned value of 2.58 ug Setot/g as selenomethionine. We have also found that 73% of the total Se in a commercial Se yeast tablet (labeled to contain "organic selenium") was present as Semet [153 + 21 ug SeSemet/g (n=23)]. Thus, these two materials contain significant amounts of their total Se content as Semet and would be good candidates for further study and characterization as RMs. This information will be of interest to food testing and analysis laboratories in the private and governmental regulatory sectors that are interested in determining content of selenomethionine in food and dietary supplement products.

Technical Abstract: Selenium is an antioxidant of importance in the diet, often occurring as the organic form of selenomethionine (Semet, bound to protein. We have developed a procedure for determining Semet in foods such as wheat (a good source of dietary Se) and its protein fraction, gluten. This method is based upon the reaction of CNBr to cleave the CH3Se-functional group and form the volatile compound, CH3SeCN. Addition of isotopically enriched 74Semet to an analytical sample, allows a determination of the naturally occurring protein bound 80Semet by GC/IDMS without a protein digestion step. For this method to be widely useful, appropriate reference materials (RM) must be available. We have examined several candidates. Wheat Gluten (NIST RM 8418) contains 40-60% of its assigned value of 2.58 ug Setot/g as selenomethionine. We have also found that 73% of the total Se in a commercial Se yeast tablet (labeled to contain "organic selenium) was present as Semet [153 + 21 ug SeSemet/g (n=23)]. Thus, these two materials contain significant amounts of their total Se content as Semet and would be good candidates for further study and characterization as RMs. In addition to matrix standards for Semet, we have examined a candidate standard sample of pure Semet being prepared by the USP. We have also shown that this method will allow the determination of Se-(methyl) selenocysteine, whose biological role is of recent interest.

Last Modified: 10/24/2014
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