Chiral separation and identification of selenoamino acids in brazil nuts by HPLC-ICP-MS and ES-MS: A racemization study of selenoamino acid species

WUILLOUD, RODOLFO G.; KANNAMKUMARATH, SASI S.; ALTAMIRANO, JORGELINA C.; CARUSO, JOSEPH A.

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Simposio; 5th INTERNATIONAL SYMPOSIUM ON SPECIATION OF ELEMENTS IN BIOLOGICAL, ENVIRONMENTAL AND TOXICOLOGICAL SCIENCES 2004 WINTER CONFERENCE ON PLASMA SPECTROCHEMISTRY; 2003

University of Oviedo

Increasing evidence suggests that nut consumption can make beneficial contributions to human health1, 2. This is understandable considering that nuts have bioactive constituents such as plant proteins, dietary fiber, and micronutritients. High concentration levels of selenium have been found in Brazil nuts (Bertholletia excelsa)3. Moreover, studies on absorption and excretion of selenium in humans who consumed Brazil nuts confirmed that only about 54% of the total selenium present in these nuts was eliminated in urine. Therefore, nuts containing appreciable amounts of Se could be considered as a possible supplement. Initial studies have begun in order to identify and determine the selenoamino acids naturally occurring in nuts4, 5.Additionally, it is well known that the biochemistry of living organisms exhibits enantioselectivity and it is possible to establish differences between D- and L-selenoamino acids showing different absorption kinetics and somewhat different metabolic pathways. In fact, some reports indicate that L-SeMet and L-SeCys are more toxic than D-SeMet and D-SeCys, respectively. Therefore, separation and determination of these selenoamino acids by their enantiomeric form is of interest. Racemization of amino acids is a phenomenon than can occur during sample preparation prior to the analysis6. Despite these possibilities, racemization studies of the selenium species during the several analytical steps (mainly extraction and hydrolysis) have not been carried out.In the present work, the enantiomeric presence of selenoaminoacids in Brazil nuts was studied. The underivatized selenoamino acids were determined by coupling on-line high-performance liquid chromatography (HPLC) to inductively coupled plasma mass spectrometry (ICP-MS). An HPLC column with a chiral crown ether stationary phase [CROWNPAK CR(+)] and a mobile phase containing HClO4 were used. A study to evaluate possible conversion of selenoamino acids enantiomers during different conventional hydrolysis sample pretreatments was undertaken. The enantiomeric conversion and possible decomposition of selenomethionine and selenocystine species that may be present in nut samples were determined under different hydrolysis conditions. The enantiomeric selenoamino acids species and their possible decomposition products were effectively identified by using electrospray-mass spectrometry (ES-MS). (1) Kris-Etherton, P. M.; Zhao, G. X.; Binkoski, A. E.; Coval, S. M.; Etherton, T. D. Nutrition Reviews 2001, 59, 103-111.(2) Fraser, G. E. Asia Pacific Journal of Clinical Nutrition 2000, 9, S28-S32.(3) Ip, C.; Lisk, D. J. Nutrition and Cancer-an International Journal 1994, 21, 203-212.(4) Vonderheide, A. P.; Wrobel, K.; Kannamkumarath, S. S.; B'Hymer, C.; Montes-Bayon, M.; De Leon, C. P.; Caruso, J. A. Journal of Agricultural and Food Chemistry 2002, 50, 5722-5728.(5) Kannamkumarath, S. S.; Wrobel, K.; Vonderheide, A.; Caruso, J. A. Analytical and Bioanalytical Chemistry 2002, 373, 454-460.(6) Liardon, R.; Hurrell, R. F. Journal of Agricultural and Food Chemistry 1983, 31, 432-437.