2006 Annual Report
The essential nature of genetically coded amino acids containing sulfurs (methionine and cysteine) and selenium (Se)(selenocysteine) is well established. However, the health promoting effects of non-genetically coded sulfur and selenium amino acids (i.e., amino acid secondary metabolites) is unproven. The lack of conclusive proof is largely due to a lack of data on the levels of these compounds in commonly consumed plant materials. A method, or series of methods, is needed to determine all S and Se amino acids and amino acid secondary metabolites in plant materials. More complete data is needed for methionine and cysteine in the National Nutrient Database for Standard Reference (NNDSR) and a provisional database is needed for selenocysteine, selenomethionine, and selected non-protein, amino acid secondary metabolites.
The field of nutrition and public health will benefit from a better understanding of the distribution of S and Se in proteins, free amino acids, and amino acid secondary metabolites in foods. New data in the National Nutrient Database will provide the public with accessible information on the specific S and Se components of foods. There will be improved knowledge of the exchange of S and Se in biological systems. The field of analytical chemistry will have more accurate and comprehensive methods for the determination of S and Se compounds in foods.
Year 2 (FY 2005) *Continue development of in-house standards. *Continue development of methods for free amino acids. *Continue evaluation of the CNBr method for methylselenoamino acids (selenomethionine).
Year 3 (FY 2006) *Continue development of in-house standards. *Continue development of methods for free amino acids. *Initiate development of a total sulfur method. *Continue evaluation of the CNBr method for methylselenoamino acids.
Year 4 (FY 2007) *Continue development of in-house standards. *Complete evaluation of the CNBr method for methylselenoamino acids. *Complete development of methods for free amino acids. *Continue development of a total sulfur method. *Initiate development of method for determination of S and Se amino acids in proteins. *Determine methylselenoamino acids in yeast and other materials using CNBr Methods.
Year 5 (FY 2008) *Continue development of a total sulfur method. *Continue development of method for determination of S and Se in proteins. *Continue determination of S and Se in foods for database. *Continue to apply CNBr method to determine methylselenoamino acids to develop database for these components in selected foods and dietary supplements.
Free amino acid content of garlic and of broccoli: the free amino acid composition was reported for 11 examples of 2 garlic sub species and in selenium enriched broccoli florets, harvested from plants grown on soil fertilized with 4 levels of sodium selenate. Glutamine was the predominate amino acid in all except one sample of garlic, with hardneck garlic having greater methiin, alliin and total free amino acids, compared to softneck garlic. Total selenium in broccoli ranged from 178 mmol/kg (dry wt) for the control to 479 mmol/kg(dry weight) for the highest of four levels of selenate fertilization. The highest level of fertilization (with the highest level of broccoli Se content) had extremely high levels of glutamine (and higher levels of serine), compared to the other treatments. This is the first report of the influence of selenium fertilization on free amino acid composition of broccoli, and will direct attention of scientists interested in the influence of fertilization treatments on content of free amino acids in broccoli.
Data to assign values for the selenomethionine (Semet) content in a new Certified Reference Material (CRM)- Selenized Yeast (SELM-1; available since December 2005, by the National Research Council of Canada) was generated using the unique Food Composition Laboratory (FCL) methodology to determine Semet in foods by reaction with cyanogen bromide (CNBr), incorporating isotope dilution mass spectrometry with a 74Se labeled Semet. Biological availability, metabolism, and potential health benefits of the essential element Se is highly dependent upon its chemical form in the diet. Selenium is of growing nutritional interest; diets augmented with Semet have been shown to reduce the risk of prostate cancer, and a major National Institutes of Health (NIH) clinical trial (SELECT Trial) is evaluating the efficacy of Semet in cancer prevention. Appropriate standards to assure accuracy of the determination of these chemical forms of selenium in foods have not previously been available. Availability of this CRM with Se species information will greatly assist the general food analysis community to assure accuracy of their results.
Initiated the development of a method for analysis of protein bound amino acids, using the free amino acid method described above, following digestion/acid hydrolysis of the protein.
Evaluated a pulsed flame photometric detector as a S- and Se-specific detector in gas chromatography.
The CNBr method was applied to the determination of selenomethionine (Semet) in a variety of wheat flour reference materials from the National Institute Standards and Technology (NIST) (wheat gluten, Durum wheat, hard red spring wheat, and soft winter wheat). Despite total Se concentrations differing by as much as a factor of 45, the Semet content was consistently about 55% of total Se. If this consistency can be confirmed in a variety of wheat cultivars commonly on the market, it will be significantly easier to evaluate total Semet dietary intake from wheat (a major source of Se in the diet) by simply measuring Se content of wheat.
FCL developed a routine method for the determination of free sulfur- and selenium- containing primary and secondary amino acids in foods. Secondary metabolite amino acids are not incorporated into proteins, are precursors for a wide variety of bioactive compounds that may have a significant impact on human health, and are not quantified in commonly consumed foods. A method was developed, based on a commercial kit (using ethylchloroformate derivatization and gas chromatography), that can determine methionine, cysteine, selenomethionine, selenocysteine, methyl selenocysteine, and alliin (the active sulfur component in garlic). This method will allow the FCL to rapidly survey foods for the free amino acids and establish a database and will allow others to evaluate the efficacy of these compounds in enhancing human health.
Wolf, W.R., Goldschmidt, R.J. 2006. Determination of selenomethionine by digestion with methanesulfonic acid, reaction with CNBr and analysis by GC-isotope dilution mass spectrometry [abstract]. 6th International Symposium on Speciation of Elements in Biological, Environmental, and Toxicological Sciences, Bialowieza, Poland. June 2006.
Mester, Z., Willie, S., Sturgeon, R., Caruso, J.A., Fernandez, M., Fodor, P., Goldschmidt, R.J., Goenaga-Infante, H., Lobindki, R., Wolf, W.R. 2006. Certification of a new selenized yeast reference material (selm-1) for methionine, selenomethinone and total selenium content and its use in an intercomparison exercise for quantifying of these analytes. Analytical and Bioanalytical Chemistry. 385(1):168-180.