Changes in Selenium Speciation Associated with Increasing Tissue Concentrations of Selenium in Wheat Grain

Abstract

Wheat (Triticum aestivum) collected in the Nawanshahr-Hoshiarpur Region (Punjab, India) showed the highest selenium concentrations ever recorded in cereal grains (29-185 microg g(-1)). There was a strong positive relationship between the selenium content in shoots and that in kernels, showing that grain selenium concentration can be predicted from that in the vegetative tissues of the plant. The identity and content of the selenocompounds in the grain samples and in wheat-based reference materials were investigated by HPLC-ICP-dynamic reaction cell-MS. Reversed-phase, cation exchange, and anion exchange HPLC were used to separate the selenium species after ultrasound-assisted enzymatic extraction with an ultrasonic probe. Selenomethionine and selenate accounted for 72-85% and 2-6% of the sum of the selenium species, respectively. The proportion of organic Se species varied with increasing Se content; namely, SeMet showed a relative reduction whereas the other organoselenium compounds increased up to 18-22% of the total chromatographed selenium. Se-methyl-selenocysteine was detected as a minor compound (0.2-0.5%) in high-Se wheat by both reversed-phase and cation exchange HPLC using retention time matching with the standard substance spiked to the sample extracts. Regular consumption of locally produced wheat-based food items may lead the population of the study area to an excessive intake of selenium. On the other hand, the large predominance of selenomethionine shows that local wheat can be a promising raw material for naturally enriched products to be used to supplement human and animal diets in low selenium areas.

Characterization of selenium-enriched wheat by agronomic biofortification

“…As shown in Table 3, SeMet was the major Se species found in all samples, which is in agreement with Cubadda et al (2010) and Hart et al (2011), who have stated that about 75 and 60 %, respectively, of the total Se present in wheat flour is in the form of SeMet. Even if the matrix material of our samples cannot be strictly viewed as typical (commercial) wheat flour, 70 to 100 % of their total Se is in the form of SeMet.…”

Bioaccessibility of selenium from Se-rich food grains of the seleniferous region of Punjab, India as analyzed by instrumental neutron activation analysis

“…The Se concentrations of the samples investigated in this study appear to be the highest ever recorded in cereal grains for human consumption, similar to wheat reported earlier by our group (Cubadda et al, 2010;Sharma et al, 2009). These levels of intake might be leading to chronic toxic effects of Se accumulation in human through Se-rich food grains and livestock fed on rice and maize straw as fodder.…”

“…The uncertainties quoted in Table 1 are the standard deviations at + 1 s confidence limits obtained from three independent sample analyses and the percentage relative standard deviations are in the range of 1.5-5%. INAA quantification of Se in cereal grains, as reported by this group (Sharma et al, 2009), was found to agree with quantification by ICP-MS in the case of wheat (Cubadda et al, 2010).…”

“…It is worth noting that since tolerance to Se toxicity varies depending on several factors, notably soil properties and sulphate supply (Lyons, Stangoulis, & Graham, 2005;Terry, Zayed, De Souza, & Tarun, 2000) threshold, Se concentrations may not be the same in other areas with different soil conditions. However, risk characterization of dietary Se exposure based on intake calculations, using realistic consumption figures of wheat-based products, showed that the population of the seleniferous belt of the NawanshahrHoshiarpur region may largely exceed the tolerable TUL for Se (Cubadda et al, 2010).…”

“…However, majority of the studies are associated with low Se food sources, with limited studies on naturally enriched sources such as cereals. We have recently reported the bioaccessibility and the speciation of Se-rich wheat from the Seleniferous region of Punjab, India (Cubadda et al, 2010). It is to be noted that SeMet was the major Se species in the wheat grains and this compound has a lower chronic toxicity compared to other selenocompounds, such as selenocysteine (SeCys 2 ) or selenate (Se IV ), in animal studies (Barceloux, 1999).…”