In order to assess the benefit or toxicity of chromium in dietary supplements, trivalent chromium and hexavalent chromium must be measured and verified with mass balance (sum of both species equaling total chromium). This is necessary because dietary supplements report trivalent chromium, an essential trace element, as an ingredient, but hexavalent chromium, a toxic carcinogen, may also be present. Because trivalent chromium is stable in acidic conditions and hexavalent chromium in alkaline conditions, interconversions between species occur and increase the difficulty of quantification. Therefore, EPA Method 3060A was first performed to extract hexavalent chromium. Then, EPA Method 3052 was performed on the residue to digest the remaining trivalent chromium. Speciated Isotope Dilution Mass Spectrometry (SIDMS) with Ion-Exchange Chromatography-Inductively Coupled Plasma-Mass Spectrometry (IC-ICP-MS) was used to account for interconversions as well as determination of trivalent and hexavalent chromium concentrations in the studied samples. Mass balance indicated that the analyzed supplements contained hexavalent chromium ranging from 0 to 16% of the total chromium content. / Bayer School of Natural and Environmental Sciences / Environmental Science and Management (ESM) / MS / Thesis

In order to assess the benefit or toxicity of chromium in dietary supplements, trivalent chromium and hexavalent chromium must be measured and verified with mass balance (sum of both species equaling total chromium). This is necessary because dietary supplements report trivalent chromium, an essential trace element, as an ingredient, but hexavalent chromium, a toxic carcinogen, may also be present. Because trivalent chromium is stable in acidic conditions and hexavalent chromium in alkaline conditions, interconversions between species occur and increase the difficulty of quantification. Therefore, EPA Method 3060A was first performed to extract hexavalent chromium. Then, EPA Method 3052 was performed on the residue to digest the remaining trivalent chromium. Speciated Isotope Dilution Mass Spectrometry (SIDMS) with Ion-Exchange Chromatography-Inductively Coupled Plasma-Mass Spectrometry (IC-ICP-MS) was used to account for interconversions as well as determination of trivalent and hexavalent chromium concentrations in the studied samples. Mass balance indicated that the analyzed supplements contained hexavalent chromium ranging from 0 to 16% of the total chromium content. / Bayer School of Natural and Environmental Sciences; / Environmental Science and Management (ESM) / MS; / Thesis;

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Thesis (M.S.) in Food Science and Human Nutrition--University of Maine, 2002. / Includes vita. Bibliography: leaves 43-48.

The influence of microbial phytase on growth performance, availability of macro and trace minerals, apparent ileal digestibility (AID) and apparent "fecal" digestibility (AFD) of amino acids (AA) and CP were investigated. The optimum level of dietary Ca and P for the maximum efficacy of supplemental phytase in broiler chickens was also studied. Phytase supplementation (600 U/kg) to a low P diet increased $(P 0.05)$ on feed efficiency in broiler chickens at 21 d. The efficacy of phytase, particularly in stimulating growth, was higher in male than female chickens. The relative retention of Ca, P, Cu, Zn and N increased by addition of phytase to a low P diet but phytase had no effect $(P >0.05)$ on the retention of Mg, Mn and Fe. Phytase supplementation increased $(P 0.05)$ on plasma Zn, Cu, and Mg. Phytase increased $(P 0.05)$ on mineral proportions in the tibia ash; however, it increased $(P 0.05)$ on AID of any of the AA in male chickens. Addition of phytase did not have any effect $(P > 0.05)$ on AFD of any of the AA in male chickens but increased $(P 0.05)$ on either AID or AFD of CP and AA at 21-d. In summary, phytase supplementation increased the growth performance, availability of P, Ca, Cu, Zn and N, plasma P, and tibia ash and reduced plasma Ca; it also increased the AID and AFD of most of the AA, particularly in female chickens at 28-d. The efficacy of microbial phytase was high when dietary P and Ca levels were low.

Selective isolation protocols of selenium (Se) species integrated to Se specific atomic absorption spectroscopy (AAS) detection were developed and optimized for Se speciation in food supplements, including selenized yeasts. By ultrafiltration, 69.18% of Se in the extract was found as a low molecular weight soluble form, the remaining 30.82% was bound to high molecular weight components. After a cation-exchange chromatography of the ultrafiltrate, 3.77% of the Se in the extract was found in the aqueous washings of the column indicating the presence of free inorganic anions of Se; the 65.41% of Se retained on the column corresponded to the free organic Se cations. The limit of detection for the HPLC-THG-AAS system was 1.85 ng of Se. Se was shown to be widely distributed over all the proteins with one sharp peak corresponding to the free forms of Se. Four major peaks were found at MW $>$ 250 000 Da (15.97% of Se recovered), between 102 330 and 117 490 Da (7.06%), between 48 977 and 53 703 Da (12.71%) and close to the dye migration band (17.25%). / Selective isolation and HPLC-AAS protocols were also developed and optimized for the determination of free organic forms e.g. selenomethionine (SeMet), selenocystine (SeCystine) and inorganic forms of selenium in aqueous solutions, and in complex matrices such as nutritional supplements and mixtures of free amino acids. The selenoamino acid in alkaline solution was first derivatized with 1-fluoro-2,4-dinitrobenzene. After removal of excess of reagent by partitioning with diethyl ether, the N-dinitrophenyl (DNP)-derivatized selenoamino acid was acidified and extracted with diethyl ether. Inorganic Se(IV) was extracted from the acidic aqueous phases by complexation with 1,2-phenylenediamine, forming a piazselenol. Se derivatives were determined selectively by HPLC-THG-AAS. A selective chromatographic mechanism based on $ pi$-electron interactions was optimized using a silica stationary phase derivatized with p-nitrophenyl moieties. Co-injections of DNP-SeMet, DNP-SeCystine and piazselenol save retention times of 3.7, 4.0 and 4.9 min, respectively, using a methanolic mobile phase containing 1.5% triethylamine and 0.013M acetic acid. Primary analytical validation parameters including stability, linearity and limits of detection were obtained using purified DNP-SeMet, DNP-SeCystine and piazselenol standards which were characterized by $ sp1$H-, $ sp{13}$C- and $ sp{77}$Se-NMR analysis and/or fast atom bombardment MS techniques. The calibration graphs for sequential dilutions of these Se standards were linear and the limits of detection from the resultant calibration graphs were 17 ng, 0.21 ng and 18.53 ng of Se, respectively. The purified DNP-SeMet and DNP-SeCystine were found to be photosensitive. The recovery of SeMet, SeCystine and inorganic Se from the stock solutions and/or nutritional supplements was virtually quantitative. In the presence of a 500-fold excess of other amino acids, the recovery of SeMet and SeCystine (96.1 $ pm$ 3.9% and 98.08 $ pm$ 4.2%, respec

Two trials were conducted in order to assess the efficacy of microbial phytase supplementation in improving the bioavailability of certain nutrients in the diet of early weaned piglets. In trial I, a low-phosphorus, corn-soybean meal diet supplemented with phytase significantly improved the apparent digestibilities of phosphorus (P, p = 0.0004) and calcium (Ca, p = 0.04). The average daily gain (ADG) and feed conversion ratio (FCR) were also improved by supplemental phytase. In trial II, addition of acetic acid to the low-P plus phytase diet further improved the apparent digestibilities of P and Ca (gp = 0.01, p = 0.02, respectively). Furthermore, the apparent digestibility of copper was also significantly improved by acetic acid addition. As a consequence, the piglets fed this treatment showed the best growth performance. Acidification of a diet which provided the NRC recommended levels of available P significantly improved the apparent digestibilities of protein and most of the minerals (P, Fe, Zn, Cu and Mn) but it was not reflected in improved growth performance. These results indicate that microbial phytase not only released P from the phytic acid molecule but it also cleaved other minerals bound to this complex.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references.

Thesis (Ph.D.)--Baylor University, 2007. / Includes bibliographical references (p. 134-146).

Thesis (Ph.D.)--Baylor University, 2007. / Includes bibliographical references (p. 145-152).