4. Conclusions
A HPLC–ESI–MS-based method for the speciation of selenium in soybean
was described. For Se-MeSeCys and Se-Met, the fragmenting voltage
and collision energy were optimized. All species were monitored by
the selected MRM mode in which the precursor ions and product ions
were selected: MRM of ion pairs with m/z values of 184–167 were characteristic
of Se-MeSeCys while those with m/z values of 198–181 were
characteristic of Se-Met. The result showed that Se-MeSeCys was the
main selenoamino acid in the soluble fraction of soybean protein, and
accounted for 66.4% of the selenium in Se-protein. Se-Met was detected
at a much lower concentration than Se-MeSeCys. Thus, soybean could
be a valuable dietary source of Se-MeSeCys, the species associated
with cancer-preventive properties. Further study is in progress to
study the speciation of organic selenium using other extraction and purification
methods.