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W R Wolf

Publications and source records attributed to W R Wolf.

At least 19 recordsLinked to original sources
PubMed2001

Selenomethionine content of candidate reference materials.

Selenium has been identified as an antioxidant of importance in the diet. Accurate determination of its chemical forms depends on the availability of suitable reference materials (RMs). Two candidate reference materials for determination of selenomethionine (Semet) in food-related materials, a standard wheat gluten sample (NIST RM 8418 Wheat Gluten) and a commercial selenium enriched yeast, have been examined by use of a gas chromatography-isotope dilution mass spectrometry (IDMS) procedure, after treatment of the matrix with 0.1 mol L(-1) hydrochloric acid containing stannous chloride, addition of CNBr, and extraction with chloroform. This procedure results in cleavage of the CH3Se group to form volatile CH3SeCN. Addition of isotopically enriched 74Semet to an analytical sample enables estimation of the naturally occurring protein-bound 80Semet by IDMS without a protein-digestion process. We found that the Wheat Gluten RM contains a significant amount of Semet as a portion of its assigned value of 2.58 microg Se(total g(-1). Commercial selenium yeast tablets are labeled as containing an elevated level of "organic selenium", usually as Semet. The sample we investigated contained 210 microg Se(total) g(-1) sample as determined separately by IDMS, measuring elemental selenium after digestion. 73% of this total (153 +/- 21 microg Se(semet) g(-1); n = 23) was present as Semet. Thus, these two materials contain significant amounts of their total selenium content as Semet and would be good candidates for further study and characterization as reference materials for determining this important food component. The CNBr reaction used will also enable the determination of Se-(methyl)selenocysteine, the biological role of which is of recent interest. In addition to matrix RMs for Semet, it is important to have standard materials of the pure substance. We have examined a sample of a candidate standard material of selenomethionine being prepared by the USP. It was confirmed that this material is pure selenomethionine.

Cold Temperature↗
PubMed2001

Matching reference materials with AOAC International methods of analysis.

Proper implementation and use of validated analytical methodology with use of appropriate reference materials (RM) is a preferred means of helping to ensure equivalent analytical method performance in diverse laboratories. Choice of an appropriate RM that not only matches the analyte and matrix of the required determination, but also has been demonstrated to be within the applicability of a specific analytical method, are key factors. In response to numerous requests since its founding in 1993, the Technical Division on Reference Materials (TDRM), AOAC International is implementing a program for recognizing the matching of specific reference materials to specific AOAC methods of analysis. This recognition is accomplished by means of a thorough peer-reviewed selection system, under the auspices of the AOAC official methods board and the executive committee of the TDRM. Potential RM/method matching (RM/MM) proposals will be submitted to an RM/MM committee. After technical review of the suitability of the proposed RM by the RM/MM committee, acceptable matches are recommended for review by the current AOAC process responsible for review and recognition of new methods and modifications to existing AOAC methods of analysis. Several trial matches have been used to develop and test this system. The end product of this effort will ultimately be made available as either a stand-alone document, a section of the AOAC Official Methods of Analysis, or a site within the AOAC web site listing recognized matches.

Journal Article↗
PubMed1995

Synthesis of a selenomethionine peptide and a preliminary study of transport into Escherichia coli monitored by high-performance liquid chromatography.

The tripeptide Gly-SeMet-Gly has been synthesized by a combination of solution and solid-phase methods. Increase in weight of the resin was very nearly theoretical, and purification was straightforward. Its absorption was compared to that of the corresponding peptide, Gly-Met-Gly, in E. coli using HPLC ion-exchange separation and fluorometric determination of the disappearance of peptides in the culture medium and the appearance of methionine and selenomethionine in the same culture medium. As E. coli are not known to possess extracellular peptidases, and in fact have been shown to possess transport systems for peptides, this absorption is interpreted as transport of the peptide through the cell wall and membrane into the cytoplasm, endohydrolysis of the peptide, and efflux of the peptides' amino acids. Uptake of both peptides was approximately equal, but was slowed when both peptides were present simultaneously.

Amino Acid Sequence↗
PubMed1994

Optimization of an Escherichia coli formate dehydrogenase assay for selenium compounds.

A microbiological assay to detect different chemical compounds of selenium for potential future use in the study of the distribution of these chemical forms in foods is being developed. This assay is based on the detection, by infrared analysis, of CO2 in a culture of Escherichia coli when the bacteria are grown in the presence of various selenium compounds. The CO2 production is the result of selenium-dependent formate dehydrogenase activity, which catalyzes oxidation of formic acid produced during glucose metabolism. Smooth response curves were generated over several orders of magnitude for selenocystine, selenite, and selenomethionine. The assay detects selenium concentrations (above background) as low as 1.5 nM for selenocystine and selenite and 4 nM for selenomethionine in minimal medium. Detection of selenomethionine was enhanced (to a sensitivity of 1.5 nM) by the addition of methionine to minimal medium and was enhanced even further (to a sensitivity of 0.8 nM) by the addition of a defined mixture of amino acids. Selenomethionine could be assayed in the presence of an amino acid concentration which is proportional to the amino acid/elemental selenium ratio found in a wheat gluten reference material (NIST SRM 8418). This implies that the assay can detect selenium compounds in a variety of foods at low concentrations, avoiding the background CO2 production caused by high concentrations of non-selenium-containing amino acids. The observation that methionine enhanced selenomethionine availability for formate dehydrogenase synthesis supports studies in animals demonstrating that methionine controls selenomethionine incorporation into selenoenzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1987

Preparation of a mixed human diet material for the determination of nutrient elements, selected toxic elements and organic nutrients: a preliminary report.

Using 201 foods from the United States Food and Drug Administration's Total Diet Study (FDA TDS), a mixed diet composite (USDIET-I) was prepared to represent the intake of 25-30-year-old males in the United States. Proximate analyses, phytate determination, and assays for nutrient elements and selected toxic elements, as well as organic nutrients were carried out on this composite. As part of a quality control exercise for a coordinated research program, atomic absorption spectrophotometry, inductively coupled atomic emission spectrometry, colorimetry and neutron activation analysis were used to determine up to 30 elements in this diet material. A comparison of the daily intakes of As, Ca, Cd, Cu, Fe, Hg, K, Mg, Mn, Na, P, Se and Zn from the composite USDIET-I shows excellent to good agreement with FDA TDS values calculated from results of single food analyses. These USDIET-I results demonstrate the feasibility of the mixed diet concept as a viable approach for a reliable assessment of daily intakes, especially for a number of elements such as Cd, Cr, Hg and Mo that occur at low concentrations in individual food products. Simultaneously, stability of some organic nutrients during storage was also investigated. Initial findings suggest that this program may also be useful in the development of reference materials for organic nutrients, for which there is a great need. These aspects are discussed.

Adult↗
PubMed1987

Selenium content of a core group of foods based on a critical evaluation of published analytical data.

References published since 1960 that report analyses of selenium in foods were collected and evaluated according to criteria in five categories: number of samples, analytical method, sample handling, sampling plan, and analytical quality control. Data were grouped by food item and rated according to the criteria that had been developed specifically for evaluating the quality of selenium data. Ratings assigned to the data from each study yielded a Quality Index, indicating which data would be included in the calculation of the mean selenium value for each food item. The Quality Indexes for acceptable studies were summed to determine a Confidence Code, intended to indicate the relative degree of confidence the user can have in each mean selenium value. The selection of selenium core foods was based on their selenium concentration and frequency of consumption. Foods were ranked by multiplying selenium concentration by the amount consumed by the 36,255 individuals who provided 3-day dietary intake data in the U.S. Department of Agriculture's 1977-78 Nationwide Food Consumption Survey. Mean, minimum, and maximum selenium values, Confidence Codes, ranks, and references have been compiled for 114 food items. The five most highly ranked food aggregates (beef, white bread, pork, chicken, and eggs) provided half of the selenium accounted for in the diets of the survey respondents.

Diet↗
PubMed1981

Selenium in self-selected diets of Maryland residents.

The mean selenium level in six self-selected, daily diets chosen by each of 22 free-living Maryland residents was 81 +/- 41 microgram. per day. Diets that were higher in selenium also were significantly higher in copper, iron, magnesium, and manganese and slightly higher in zinc. However, in general, the levels of these minerals were low, probably because of low consumption of grains, legumes, and nuts. Diets higher in selenium contained more fish and less processed meat than other diets.

Diet↗
PubMed1979

Zinc and copper in self-selected diets.

Levels of zinc and copper in the self-selected diets of twenty-two men and women were determined by atomic absorption spectrophotometry. Sixty-eight per cent of the subjects consumed less than two-thirds of the recommended allowance for zinc (15 mg). Eighty-one per cent consumed less than two-thirds of the suggested level of copper (2.0 mg). Average daily intake of protein exceeded the recommended allowance. However, the mean zinc:calorie ratio for those subjects was only 4.19 mg. per 1,000 kcal. Using the recommended allowances for zinc and for energy, the zinc:calorie ratio would be 6.5 mg. per 1,000 kcal. For copper, the suggested nutrient density is 0.85 mg. per 1,000 kcal vs. the 0.50 mg. per 1,000 kcal observed in this study. These metallo:calorie ratios indicate that the nutrient density of these two trace elements in the diet is low and that diets supplying adequate amounts of energy and protein do not guarantee adequate levels of zinc and copper.

Adolescent↗
PubMed1977

Coupled gas chromatography-atomic absorption spectrometry.

The specific, precise detection of volatile metal chelates has been obtained by coupling the effluent from a gas chromatograph directly to the burner head of a commerical atomic absorption spectrometer (AAS). Quantitation of chromium in the nanogram range has been accomplished with a detection limit of 1.0 ng. The chelation-extraction-gas chromatographic separation procedure coupled with the selective detection by AAS gives a relatively interference-free system that has been used to quantitatively analyse for chromium in standard biological materials NBS SRM 1571 Orchard Leaves and SRM 1569 Brewers Yeast. Metal chelates of iron, copper and cobalt have also been detected by this system.

Chromatography, Gas↗