Stability of Se species in plant extracts rich in phenolic substances |
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Authors: | Petra Cuderman Vekoslava Stibilj |
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Institution: | (1) Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia; |
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Abstract: | Since there is growing awareness of the strong dependence of the antioxidative function of selenium (Se) upon its chemical
form, the stability of Se species during sample preparation is an important factor in obtaining qualitative and quantitative
results. Many plant samples are rich in phenolic compounds (antioxidants), but data about their effect on specific Se species
in extracts of plant samples are scarce. Therefore, the aim of this study was to investigate the effect of the most common
phenolic substances in plant parts, namely tannin and the flavonoid rutin, on the concentration and/or transformation of several
Se species (SeMet, SeCys2, SeMeSeCys, Se(VI) and Se(IV)) during sample preparation (24 h incubation at 37 °C) and storage (4 days at 4 °C). Moreover,
the effect observed was then studied in a real sample, buckwheat, because this plant is known as a rich source of phenolics,
especially tannin and rutin. Se speciation was carried out by on-line coupling of ion-exchange HPLC-ICP-MS after water and
enzymatic (protease) hydrolysis. The results showed that the ratio between the two antioxidants has an important role. When
the antioxidants were present together, the response for Se(IV) was observed to start to decrease only at a ratio of rutin
to tannin of 1:100 (w/w), indicating the ratio between antioxidants in buckwheat seeds. After water extraction, only 40% and after enzymatic extraction
80% of Se(IV) remained, but no other Se compound was detected with the system used. Furthermore, the extracts were not stable
during storage at 4 °C. Signals for other Se species were stable. The results obtained for buckwheat seeds showed a decrease
in Se(IV) response during sample preparation and storage, comparable to the one obtained with the experiments performed in
vitro. However, Se species in extracts of other buckwheat parts (leaves, stems and sprouts) were stable. These results indicate
that reactions in the extraction process and during storage may affect Se speciation and may result in misidentifications
and inaccurate values. |
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