Stability of Se species in plant extracts rich in phenolic substances

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, SeCys(2), SeMeSeCys, Se(VI) and Se(IV)) during sample preparation (24 h incubation at 37 degrees C) and storage (4 days at 4 degrees 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 degrees 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.

Atomic spectrometry update. Elemental speciation

“…53 For buckwheat seeds, containing a ratio of rutin to tannin of 1 : 100 (w/w), the response for Se IV decreased during the extraction: only 40% remained after extraction with water, and 80% remained after protease extraction; however, no other Se compounds were detected by HPLC-ICP-MS. The extracts were unstable with respect to the Se IV content during refrigeration, whereas other Se species were stable.…”

Fagopyrin and rutin concentration in seeds of common buckwheat plants treated with Se and I / Vsebnost fagopirina in rutina v semenih navadne ajde tretirane s selenom in jodom

“…The role of rutin is scavenging free radicals and anti-fungal activity (Suzuki et al 2015). Besides flavonoids, buckwheat also contains trace elements, like Zn, Cu, Mn and Se (Cuderman & Stibilj 2010). Buckwheat has many favourable medicinal properties for humans, because of its antioxidative (Holasová et al 2002, Kreft 2016, anti-inflammatory and anticarcinogenic effects and it can also increase the strength of blood vessels (Brozmanová et al 2010).…”

Speciation of Selenium in Enriched Garlic Sprouts by High-Performance Liquid Chromatography Coupled with Inductively Coupled Plasma-Mass Spectrometry

“…An appropriate extraction method is the prerequisite for effective separation (Kápolna and Fodor 2006;Montes-Bayon et al 2006). Cuderman and Stibilj (2010) reported that only 40% of selenite in the extracts of plant samples remained after water extraction, and methylselenocysteine was not extracted by enzymatic hydrolysis, which may be due decomposition of this compound. A Tris-HCL extraction followed by acetone addition was found to be optimal for protein precipitation (Gergely et al 2006).…”