Uptake and speciation of selenium in garlic cultivated in soil amended with symbiotic fungi (mycorrhiza) and selenate |
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Authors: | Erik H Larsen Ryszard Lobinski Karin Burger-Meÿer Marianne Hansen Rafal Ruzik Lena Mazurowska Peter Have Rasmussen Jens J Sloth Olga Scholten Chris Kik |
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Institution: | 1. Department of Food Chemistry, Danish Institute for Food and Veterinary Research, 2860, S?borg, Denmark 2. CNRS UMR 5034, Hélioparc, 2, Av. Angot, 64053, Pau, France 3. Department of Analytical Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland 4. Plant Research International (PRI), Wageningen University and Research Centre, P.O. Box 16, 6700 AA, Wageningen, The Netherlands 5. Centre for Genetic Resources, The Netherlands (CGN), Wageningen University and Research Centre, P.O. Box 16, 6700 AA, Wageningen, The Netherlands
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Abstract: | The scope of the work was to investigate the influence of selenate fertilisation and the addition of symbiotic fungi (mycorrhiza)
to soil on selenium and selenium species concentrations in garlic. The selenium species were extracted from garlic cultivated
in experimental plots by proteolytic enzymes, which ensured liberation of selenium species contained in peptides or proteins.
Separate extractions using an aqueous solution of enzyme-deactivating hydroxylamine hydrochloride counteracted the possible
degradation of labile selenium species by enzymes (such as alliinase) that occur naturally in garlic. The selenium content
in garlic, which was analysed by ICP–MS, showed that addition of mycorrhiza to the natural soil increased the selenium uptake
by garlic tenfold to 15 μg g−1 (dry mass). Fertilisation with selenate and addition of mycorrhiza strongly increased the selenium content in garlic to around
one part per thousand. The parallel analysis of the sample extracts by cation exchange and reversed-phase HPLC with ICP–MS
detection showed that γ-glutamyl-Se-methyl-selenocysteine amounted to 2/3, whereas methylselenocysteine, selenomethionine
and selenate each amounted to a few percent of the total chromatographed selenium in all garlic samples. Se-allyl-selenocysteine
and Se-propyl-selenocysteine, which are selenium analogues of biologically active sulfur-containing amino acids known to occur
in garlic, were searched for but not detected in any of the extracts. The amendment of soil by mycorrhiza and/or by selenate
increased the content of selenium but not the distribution of detected selenium species in garlic. Finally, the use of two-dimensional
HPLC (size exclusion followed by reversed-phase) allowed the structural characterisation of γ-glutamyl-Se-methyl-selenocysteine
and γ-glutamyl-Se-methyl-selenomethionine in isolated chromatographic fractions by quadrupole time-of-flight mass spectrometry. |
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Keywords: | Selenium speciation Garlic HPLC– mass spectrometry Selenium enrichment Mycorrhiza |
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