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United States Department of Agriculture

Agricultural Research Service

Title: Methylseleno-Amino Acid Content of Food Materials by Stable Isotope Dilution Mass Spectrometry

Authors
item Wolf, Wayne
item Zainal, Hanna - FCL COLLABORATOR

Submitted to: Food Nutrition Bulletin of the United Nations University
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 15, 2002
Publication Date: February 2, 2002
Citation: Wolf, W.R., Zainal, H. 2002. Methylseleno-amino acid content of food materials by stable isotope dilution mass spectrometry. Food Nutrition Bulletin of the United Nations University. 23(3):120-123

Interpretive Summary: Selenium, an important dietary nutrient, is found in many food products such as grains. Se occurs in various chemical forms including amino acids with methylselenium functional groups, such as selenomethionine (Semet) and Se- (methyl) selenocystine (Metsecys). We have developed a procedure for determining methylselenium amino acids in foods such as wheat, a significant source of Se in US diets. This method is based upon the reaction of CNBr to cleave the CH3Se-functional group of Semet and Metsecys to form the volatile compound, CH3SeCN. Addition of stable isotope enriched selenomethionine to an analytical sample allows direct determination of naturally occurring protein bound Semet by GC/MS (without a protein digestion step) using highly precise stable isotope dilution techniques. We found that a Wheat Gluten Reference Material (NIST RM 1818) contains 64% and commercial selenium yeast tablets contained 73% of total Se as methylSe compounds. This information will be of interest to Food Testing Analysis laboratories in the public, regulatory and private sectors interested in testing for Selenomethionine.

Technical Abstract: Selenium , an important dietary nutrient, is found in many food products such as grains. Se occurs in various chemical forms including amino acids with methylselenium (metse) functional groups, such as selenomethionine (Semet) and Se- (methyl)selenocystine (Metsecys). We have developed a procedure for determining methylselenium in foods such as wheat, a significant source of Se in US diets. This method is based upon the reaction of CNBr to cleave the CH3Se-functional group of Semet and Metsecys to form the volatile compound, CH3SeCN. Addition of stable isotope enriched selenomethionine to an analytical sample allows direct determination of naturally occurring protein bound Semet by GC/MS (without a protein digestion step) using highly precise stable isotope dilution techniques. We found that a Wheat Gluten Reference Material (NIST RM 1818) contains 64% methylselenium of its assigned value of 2.58 ug Setotal/g, and that commercial selenium yeast tablets contained 73% of total Se as methylselenium (147 + 1-10ug, n=9). These two materials would be good candidates for further study and characterization as reference materials for determining this important food component.

Last Modified: 7/25/2014
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