Quantification, Localization,
and Speciation of Selenium
in Seeds of Canola and Two Mustard Species Compared to Seed-Meals
Produced by Hydraulic Press
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Abstract
<i>Brassica</i> plants accumulate selenium
(Se) especially
in seeds when grown in soils laden with Se. We report a chemical analysis
of Se in <i>Brassica</i> seeds (canola, Indian mustard,
and white mustard) and in their hydraulically pressed seed meals,
which are used as a Se supplement in livestock animal feeds. Complementary
techniques were used to measure total Se concentrations, to map the
localization of Se, and to quantify different Se forms. Seeds and
hydraulically pressed seed meals contained an average of 1.8 and 2.0
μg Se g<sup>–1</sup> DW, respectively. Selenium was primarily
located in cotyledons and roots of seed embryos. Microfocused Se K-edge
XANES and bulk XANES showed that seeds contained 90% of Se as C–Se–C
forms. Hydraulically pressing seeds for oil caused changes in the
forms of Se as follows: 40–55% C–Se–C forms,
33–42% selenocystine, 5–12% selenocysteine, and 11–14%
trimethylselenonium ion. Aqueous extracts of seed and seed meals were
also analyzed by SAX-HPLC/ICPMS and found to contain mainly the C–Se–C
form SeMet, but also another C–Se–C form MeSeCys, which
is of dietary pharmacological interest for cancer inhibition. In addition,
SAX-HPLC/ICPMS also detected selenocystine and selenocysteine, further
confirming the results obtained by XANES analyses