Combined speciation analysis by X-ray absorption near-edge structure spectroscopy, ion chromatography, and solid-phase microextraction gas chromatography-mass spectrometry to evaluate biotreatment of concentrated selenium wastewaters

In this study we evaluate the potential of anaerobic granular sludge as an inoculum for the bioremediation of selenium-contaminated waters using species-specific analytical methods. Solid species formed by microbial reduction were investigated using X-ray absorption near-edge structure (XANES) spectroscopy at the selenium K-edge. Furthermore, dissolved selenium species were specifically determined by ion chromatography (IC) and solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). Least-squares linear combination of the XANES spectra for samples incubated with the highest selenate/selenite concentrations (10(-3) M) show the predominance of elemental selenium and a Se(-I) selenide, such as ferroselite, the thermodynamically most stable iron selenide. In contrast, elemental selenium and Se(-II) selenides are the main species detected at the lower selenate/selenite concentrations. In each repeated fed batch incubation, most aqueous selenite anions were converted into solid selenium species, regardless of the type of electron donor used (acetate or H(2)/CO(2)) and the selenium concentration applied. On the other hand, at higher concentrations of selenate (10(-4) and 10(-3) M), significant amounts of the oxyanion remained unconverted after consecutive incubations. SPME-GC-MS demonstrated selenium alkylation with both electron donors investigated, as dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Selenite was even more alkylated in the presence of H(2)/CO(2) (maximum 2156 μg of Se/L of DMSe + DMDSe) as compared to acetate (maximum 50 μg of Se/L). In contrast, selenate was less alkylated using both electron donors (maximum 166 and 3 μg of Se/L, respectively). The high alkylation potential for selenite limits its bioremediation in selenium laden waters involving H(2)/CO(2) as the electron donor despite the fact that nontoxic elemental selenium and thermodynamically stable metal selenide species are formed.     

Critical evaluation of the ability of sequential extraction procedures to quantify discrete forms of selenium in sediments and soils

Sequential extraction procedures (SEPs) have been widely used to characterize the mobility, bioavailibility, and potential toxicity of trace elements in soils and sediments. Although oft-criticized, these methods may perform best with redox-labile elements (As, Hg, Se) for which more discrete biogeochemical phases may arise from variations in oxidation number. We critically evaluated two published SEPs for Se for their specificity and precision by applying them to four discrete components in an inert silica matrix: soluble Se(VI) (selenate), Se(IV) (selenite) adsorbed onto goethite, elemental Se, and a metal selenide (FeSe; achavalite). These were extracted both individually and in a mixed model sediment. The more selective of the two procedures was modified to further improve its selectivity (SEP 2M). Both SEP 1 and SEP 2M quantitatively recovered soluble selenate but yielded incomplete recoveries of adsorbed selenite (64% and 81%, respectively). SEP 1 utilizes 0.1 M K2S2O8 to target "organically associated" Se, but this extractant also solubilized most of the elemental (64%) and iron selenide (91%) components of the model sediment. In SEP 2M, the Na2SO3 used in step III is effective in extracting elemental Se but also extracted 17% of the Se from the iron selenide, such that the elemental fraction would be overestimated should both forms coexist. Application of SEP 2M to eight wetland sediments further suggested that the Na2SO3 in step III extracts some organically associated Se, so a NaOH extraction was inserted beforehand to yield a further modification, SEP 2OH. Results using this five-step procedure suggested that the four-step SEP 2M could overestimate elemental Se by as much as 43% due to solubilization of organic Se. Although still imperfect in its selectivity, SEP 20H may be the most suitable procedure for routine, accurate fractionation of Se in soils and sediments. However, the strong oxidant (NaOCl) used in the final step cannot distinguish between refractory organic forms of Se and pyritic Se that might form under sulfur-reducing conditions.     

Speciation of selenium in vitamin tablets using spectrofluorometry following cloud point extraction

Selenium is one of the trace and essential elements for good health but required only in a very narrow range. Hence, determination of selenium in trace level is important. In this work, cloud point extraction (CPE) with non-ionic surfactant Triton X-114 and the fluorometric ligand, 2,3-diaminonaphtalene (DAN) were used for extraction of trace amounts of organic and inorganic selenium species prior to their determination by spectrofluorometry. CPE parameters affecting complexation and phase separation were optimised. The limit of detection calculated by using nine replicate measurements of 0.020 mg/L Se solution after complexing with DAN and 10-fold CPE preconcentration was 2.1 μg/L. Accuracy of the method was checked using EnviroMat Waste Water, EU-L-2 as CRM and result was found to be in good agreement with the certified value. The suggested method can be used for selenium species of selenite, selenate, and total organic selenium at μg/L level.     

Uptake and distribution of added selenite and selenate by barley and red clover as influenced by sulphur

The uptake of added Se from selenite and selenate by barley and red clover was investigated in a pot experiment. Much more of selenate than of selenite was taken up but the Se concentrations in the plants declined more with time when selenate was the source. Increasing sulphate addition to the soil decreased the uptake of Se from selenate greatly and from selenite to a lesser extent. The ratio Se in the roots/Se in the tops shows that Se is more readily translocated from the roots when taken up from added selenate than from selenite. On the basis of these and other investigations it is concluded that selenite is a better source than selenate when the Se concentration in the plants has to be raised to a level sufficient for livestock nutrition.     

Bioavailability Assessment of Copper,Iron, Manganese,Molybdenum, Selenium,and Zinc from Selenium‐Enriched Lettuce

Cu, Fe, Mn, Mo, Selenium (Se), and Zn bioavailability from selenate‐ and selenite‐enriched lettuce plants was studied by in vitro gastrointestinal digestion followed by an assay with Caco‐2 cells. The plants were cultivated in the absence and presence of two concentrations (25 and 40 µmol/L of Se). After 28 days of cultivation, the plants were harvested, dried, and evaluated regarding the total concentration, bioaccessibility, and bioavailability of the analytes. The results showed that biofortification with selenate leads to higher Se absorption by the plant than biofortification with selenite. For the other nutrients, Mo showed high accumulation in the plants of selenate assays, and the presence of any Se species led to a reduction of the plant uptake of Cu and Fe. The accumulation of Zn and Mn was not strongly influenced by the presence of any Se species. The bioaccessibility values were approximately 71%, 10%, 52%, 84%, 71%, and 86% for Cu, Fe, Mn, Mo, Se, and Zn, respectively, and the contribution of the biofortified lettuce to the ingestion of these minerals is very small (except for Se and Mo). Due to the low concentrations of elements from digested plants, it was not possible to estimate the bioavailability for some elements, and for Mo and Zn, the values are below 6.9% and 3.4% of the total concentration, respectively. For Se, the bioavailability was greater for selenite‐enriched than selenate‐enriched plants (22% and 6.0%, respectively), because selenite is biotransformed by the plant to organic forms that are better assimilated by the cells.     

Grain accumulation of selenium species in rice (Oryza sativa L.)

Efficient Se biofortification programs require a thorough understanding of the accumulation and distribution of Se species within the rice grain. Therefore, the translocation of Se species to the filling grain and their spatial unloading were investigated. Se species were supplied via cut flag leaves of intact plants and excised panicle stems subjected to a ± stem-girdling treatment during grain fill. Total Se concentrations in the flag leaves and grain were quantified by inductively coupled plasma mass spectrometry. Spatial accumulation was investigated using synchrotron X-ray fluorescence microtomography. Selenomethionine (SeMet) and selenomethylcysteine (SeMeSeCys) were transported to the grain more efficiently than selenite and selenate. SeMet and SeMeSeCys were translocated exclusively via the phloem, while inorganic Se was transported via both the phloem and xylem. For SeMet- and SeMeSeCys-fed grain, Se dispersed throughout the external grain layers and into the endosperm and, for SeMeSeCys, into the embryo. Selenite was retained at the point of grain entry. These results demonstrate that the organic Se species SeMet and SeMeSeCys are rapidly loaded into the phloem and transported to the grain far more efficiently than inorganic species. Organic Se species are distributed more readily, and extensively, throughout the grain than selenite.     

Selenite reduction by mackinawite, magnetite and siderite: XAS characterization of nanosized redox products

Suboxic soils and sediments often contain the Fe(II)-bearing minerals mackinawite (FeS), siderite (FeCO3) or magnetite (FesO4), which should be able to reduce aqueous selenite, thereby forming solids of low solubility. While the reduction of selenate or selenite to Se(O) by green rust, pyrite and by Fe2+ sorbed to montmorillonite is a slow (weeks), kinetically limited redox reaction as demonstrated earlier, we show here that selenite is rapidly reduced within one day by nanoparticulate mackinawite and magnetite, while only one third of selenite is reduced by micrometer-sized siderite. Depending on Fe(II)-bearing phase and pH, we observed four different reaction products, red and gray elemental Se, and two iron selenides with structures similar to Fe7Se8 and FeSe. The thermodynamically most stable iron selenide, ferroselite (FeSe2), was not observed. The local structures of the reaction products suggest formation of nanoscale clusters, which may be prone to colloid-facilitated transport, and may have a higher than expected solubility.     

烟株对不同价态硒的吸收与分配

为了开发富硒烟叶生产技术和了解烟叶对硒的富集机理,采用水溶性Se（Ⅳ）（亚硒酸钠）和Se（Ⅵ）（硒酸钠）盆栽试验,探讨了烟株对硒的吸收和分配规律,以及不同价态和用量的硒对烟株生长发育的影响。结果表明,土壤施用适当浓度的两种价态硒（1～10 mg/kg）均有改善烟株形态性状和提高生物量的作用,高浓度硒（20～30 mg/kg）则有负面影响,且Se（Ⅵ）处理抑制效果大于 Se（Ⅳ）。相同浓度下,两种价态的硒均能有效提高烟株各部位硒含量,Se（Ⅵ）处理较 Se（Ⅳ）提高了3～30倍。土壤中的硒优先富集和分布于叶片中,其次是根系,茎秆最小。Monod方程拟合结果表明,Se（Ⅵ）处理烟株叶片、茎秆和根系最大硒含量分别是Se（Ⅳ）处理的1.83、15.81和20.98倍,烟株对Se（Ⅵ）的亲和能力显著大于Se（Ⅳ）,说明Se（Ⅵ）对烟株的生物有效性明显高于Se（Ⅳ）。     

Bioavailability of selenium in the defatted dark muscle of tuna

The content and bioavailability of selenium (Se) in the dark muscle of tuna (DMT) were studied. Fluorometric analysis showed that DMT contained 2.0-4.7 µg g^-1 Se. A large part of Se of the DMT was recovered in the dry powder of the defatted fraction prepared by successive treatment with acetone and n-hexane/ethanol. On trypsin digestion of the defatted DMT, release of Se paralleled that of nitrogen and about 70% of Se was released within 4 h. Male weanling ddY mice were fed a Torula yeast-based Se-deficient diet (basal diet) for 3 weeks, and then fed the basal diet or a diet supplemented with a 0.05-0.25 µg g^-1 Se as either sodium selenite or the defatted DMT for a further 1 week. Se contents and GSHPx activities in the liver increased gradually with increases in the amount of supplemented Se. No differences were observed between selenite and defatted DMT in the effect on Se content. At low Se levels, the effect of Se in the defatted DMT on the liver GSHPx activities was inferior to that of selenite, but at a high Se level, Se in the defatted DMT showed a greater effect. The bioavailability of Se in the defatted DMT, as assessed by slope ratio analysis using selenite as the reference Se, was 87% for the liver Se content and 168% for the GSHPx activity. The results indicate that the defatted DMT contains high levels of Se in a nutritionally available form.     

Physiological function of Se‐enriched tea fertilised with sodium selenite and naturally high‐Se tea in rats

In order to increase food selenium (Se) content, Se‐enriched tea was produced by fertilising with sodium selenite in low‐Se soil. Five groups of rats were fed a low‐Se diet supplemented with either water (Se‐deficient), sodium selenite or an aqueous extraction of low‐Se tea, Se‐enriched tea or naturally high‐Se tea. The chemical form of Se in Se‐enriched tea and the physiological function in rats fed the different Se sources were determined after 8 weeks. The results showed that organic Se accounted for 80% or more of the Se in Se‐enriched tea fertilised with sodium selenite and naturally high‐Se tea, but no significant differences in the proportion of organic Se and protein Se were found between Se‐enriched tea and naturally high‐Se tea. The Se biological utilisation rates were 65.41, 68.05 and 70.49% for sodium selenite, Se‐enriched tea and naturally high‐Se tea respectively. The Se content of blood and liver and the glutathione peroxidase (GSH‐Px) activity were significantly increased by feeding Se‐enriched tea and sodium selenite compared with low‐Se tea, but a more efficient increase in liver GSH‐Px activity was obtained with Se‐enriched tea than with sodium selenite. No significant differences were found between Se‐enriched tea fertilised with sodium selenite and naturally high‐Se tea, which proved that the biological effectiveness of Se in Se‐enriched tea was higher than that of sodium selenite in increasing liver GSH‐Px activity. Se‐enriched tea fertilised with sodium selenite in low‐Se soil gave the same biological function as naturally high‐Se tea. Therefore Se‐enriched tea is a safe and effective means of increasing the Se intake of both humans and animals in low‐Se areas. © 2000 Society of Chemical Industry     

Speciation of Se and DOC in soil solution and their relation to Se bioavailability

A 0.01 M CaCl(2) extraction is often used to asses the bioavailability of plant nutrients in soils. However, almost no correlation was found between selenium (Se) in the soil extraction and Se content in grass. The recently developed anion Donnan membrane technique was used to analyze chemical speciation of Se in the 0.01 M CaCl(2) extractions of grassland soils and fractionation of DOC (dissolved organic carbon). The results show that most of Se (67-86%) in the extractions (15 samples) are colloidal-sized Se. Only 13-34% of extractable Se are selenate, selenite and small organic Se (<1 nm). Colloidal Se is, most likely, Se bound to or incorporated in colloidal-sized organic matter. The dominant form of small Se compounds (selenate, selenite/small organic compounds) depends on soil. A total of 47-85% of DOC is colloidal-sized and 15-53% are small organic molecules (<1 nm). In combination with soluble S (sulfur) and/or P (phosphor), concentration of small DOC can explain most of the variability of Se content in grass. The results indicate that mineralization of organic Se is the most important factor that controls Se availability in soils. Competition with sulfate and phosphate needs to be taken into account. Further research is needed to verify if concentration of small DOC is a good indicator of mineralization of soil organic matter.     

Mineral substance in human nutrition. Selenium: absorption and bioavailability

In the review there are discussed results of selenium absorption studies in human and animals gastrointestinal tract. According to plenty of experimental data selenate-anion is rapidly and quantitatively absorbed upstream concentration gradient the site of absorption being predominantly ileum. This process is Na+ and energy dependent. On the contrary seleniteanion is absorbed mostly in jejunum, the rate of uptake is less than for selenate in model systems and absorption does not occur toward concentration gradient. Under physiological conditions the most part of selenite is transported as mixed thiols with glutathione and some other tissue thiol compounds. Selenium amino acids are transported by corresponding transfer systems with specificity for analogous sulfur containing amino acids. Whereas bioavailability of transition al metals salts rarely exceeds 10-20%, selenium food sources (both organic and inorganic origin) are typically high absorbable predominantly on 60% or more and in some cases almost on 100%. From this point of view selenium food sources bioavailability evaluation must take into account their metabolic retention and toxicity indicies rather than absorption ratio (such is for zinc, chromium and other metal ions).     

Dietary selenium reduces retention of methyl mercury in freshwater fish

Adverse effects from organic mercury transported along aquatic food chains are health issues in humans and other top predators. Methyl mercury in organisms at the lower food chain levels is eliminated slowly, and laboratory studies have not clarified the role of selenium in the retention of methyl mercury in fish. Here, we investigated the effects of dietary selenium on the retention of organic and inorganic mercury in freshwater fish. Addition of selenite to the food augmented elimination of methyl mercury (but not inorganic mercury) from goldfish Carassius auratus in a dose dependent manner; selenite caused methyl mercury to be lost from the general body rather than from any specific organ. Seleno-cystine and seleno-methionine (but not selenate) likewise promoted elimination of methyl mercury from goldfish. The threshold for the augmenting effect of selenite on the elimination of methyl mercury in the zebra fish Danio rerio was 0.95 μg Se g(-1) food; higher concentrations reduced retention of methyl mercury in a dose dependent manner. Selenium concentrations in the food approaching natural background levels increase the elimination of methyl mercury from fish. Thus, selenium levels in a given aquatic food chain may affect mercury contamination along the food chain.     

Speciation of selenium in selenium-enriched seeds,buckwheat (<Emphasis Type="Italic">Fagopyrum esculentum</Emphasis> Moench) and quinoa (<Emphasis Type="Italic">Chenopodium quinoa</Emphasis> Willdenow)

Buckwheat (Fagopyrum esculentum Moench) and quinoa (Chenopodium quinoa Willdenow) are widely used as food ingredients. The nutritional characteristics of these plants, i.e., high contents of proteins and amino acids suggest that selenium (Se) is preserved as selenoamino acid derivatives, in particular, selenomethionine (SeMet) in proteins, similar to selenized yeast. Therefore, buckwheat and quinoa are expected to be a good nutritional source of Se. Selenized buckwheat and quinoa were cultivated on Se-fortified soil using sparingly soluble Se salts, such as barium selenate and barium selenite. Se concentration in the edible parts of these plants was determined, and Se extraction efficiency with enzyme or alkali was evaluated. In addition, the chemical species of Se in the low molecular weight fraction of these plants were determined by HPLC-ICP-MS. Total Se concentrations in the edible parts of selenized buckwheat and quinoa were 170.4 ± 2.9 μg/g and 102.7 ± 2.4 μg/g wet weight, respectively. Thus, these selenized seeds were found to be Se accumulators. The results indicate that Se in selenized buckwheat exists mainly as SeMet, while Se in selenized quinoa exists not only as SeMet but also as selenate (Se(VI)) and non-protein forms.     

Soil selenium treatments to ameliorate selenium deficiency in herbage

Sodium selenite, sodium selenate, and sodium selenate in a pill formulation were applied to three soils known to produce Se-deficient herbage ( < 100 μg Se kg^?1 dry matter (DM)). The ability of the salts, applied in spring 1985, to ameliorate Se deficiency was followed over 3 years by taking four harvests each year. Selenate treatment at 10 g Se ha^?1 and selenate prill treatment at 20 g Se ha^?1 produced herbage with Se levels (geometric means) of between 0.57-0.86 and 1.79-1992 mg kg^?1 DM respectively in the first spring harvest after treatment. Selenite was less potent and selenite at 100 g Se ha^?1 produced a response in herbage closely similar to that of selenate at 10 g Se ha^?1. Even at 300 g Se ha^?1 the selenite treatment produced herbage with only 1.00-1.36 mg Se kg^?1 DM at the first harvest. Application of selenate in the prill form at 60 g Se ha^?1 produced herbage potentially toxic to grazing animals with 4.81-4.94 mg Se kg^?1 DM. The addition of fertiliser N to Se-treated plots increased total Se uptake at the first harvest by a factor of 4 and had a small effect on Se concentration. The Se concentration levels in herbage from Se-treated plots declined exponentially (t_1/2 = 21-43 days). On one soil derived from Lower Old Red Sandstone and lava, selenite at 300 g Se ha^?1 gave herbage with Se contents significantly above background (P < 0.05) in all harvests over 3 years.     

转基因大豆对硒的富集作用和形态分布研究

目的研究转基因大豆对硒的富集作用以及富集前后转基因大豆中硒的形态分布和形态转化。方法 采用电感耦合等离子体质谱分析转基因大豆富集前后硒的总量,采用蛋白酶提取,高效液相色谱-电感耦合等离子体质谱(high performance liquid chromatography-inductively coupled plasma-mass spectrometry,HPLC-ICP-MS)联用技术分析转基因大豆中的硒酸盐(selenate,Se VI)、亚硒酸盐(selenite,Se IV)、硒代蛋氨酸(selenomethionine,Se Met)和硒代胱氨酸(selenocystine,Se Cys)等几种硒化合物。盆栽种植试验研究转基因大豆对硒的富集作用。通过对照试验,考察大豆植株不同部位总硒含量变化和形态分布的转化情况。结果转基因大豆对硒有较好的富集作用,吸收的亚硒酸盐在大豆植株中部分转化成了硒代蛋氨酸和硒代胱氨酸。结论 了解了转基因大豆的形态分布和转化情况,可以更好地评估转基因大豆的食用安全风险并进行生物利用开发。     

Isotope fractionation of selenium during fungal biomethylation by Alternaria alternata

The natural abundance of stable Se isotopes may reflect sources and formation conditions of methylated Se. We aimed at (1) quantifying the degree of methylation of selenate [Se(VI)] and (hydro)selenite [Se(IV)] by the fungus Alternaria alternata at pH 4 and 7 and (2) determining the effects of these different Se sources and pH values on 82Se/76Se ratios (δ82/76Se) in methylselenides. Alternaria alternata was incubated with Se(VI) and Se(IV) in closed microcosms for 11-15 days and additionally with Se(IV) for 3-5 days at 30 °C. We determined Se concentrations and δ82/76Se values in source Se(VI) and Se(IV), media, fungi, and trapped methylselenides. In Se(VI) incubations, methylselenide volatilization ended before the 11th day, and the amounts of trapped methylselenide were not significantly different among the 11-15 day incubations. In 11-15 days, 2.9-11% of Se(VI) and 21-29% of Se(IV) were methylated, and in 3-5 days, 3-5% of Se(IV) was methylated. The initial δ82/76Se values of Se(VI) and Se(IV) were -0.69±SD 0.07‰, and -0.20±0.05‰, respectively. The δ82/76Se values of methylselenides differed significantly between Se(VI) (-3.97‰ to -3.25‰) and Se(IV) (-1.44‰ to -0.16‰) as sources after 11-15 days of incubation; pH had little influence on δ82/76Se values. Thus, the δ82/76Se values of methylselenide indicate the source species of methylselenides used in this study. The strong isotope fractionation of Se(VI) is probably attributable to the different reduction steps of Se(VI) to Se(-II) which were rate-limiting explaining the low methylation yields, but not to the methylation itself. The shorter incubation of Se(IV) for 3-5 days showed a large Se isotope fractionation of at least -6‰ before the biomethylation reaction reached its end. This initial Se isotope fractionation during methylation of Se(IV) is much larger than previously published.     

Effects of selenium source and level of supplementation on the performance and meat quality of lambs

Objective of this study was to evaluate the performance, the quality and oxidative stability of meat, the total Se and specific selenoamino-acids content of muscle of lambs that were fed diets supplemented from different Se sources and at different levels. Forty-eight Apennine lambs 30 day old (12.78 ± 0.94 kg) received, during a 63 day period, a total mixed ration (TMR) which was either Se unsupplemented (Control group - background only- 0.13 mg/kg Se) or supplemented with Na selenite (0.30 mg/kg Se as sodium selenite) or selenium enriched yeast (0.30 mg/kg and 0.45 mg/kg Se as Se-yeast).Growth performance, feed to gain ratio, carcass and meat quality (pH, drip and cooking losses, colour, GSH-Px activity and chemical analysis) did not show any difference between the treatments. Meat colour and oxidative stability during 9 days of refrigerated storage were unaffected by dietary supplementation, suggesting that, at the levels of Se used in this experiment, dietary Se, even from an organic source, had limited potential for reducing lipid oxidation. Selenium supplementation raised the Se content in muscle (P < 0.001) with the greatest increase when Se-yeast was fed. Although selenite increased total Se, it did not influence total or specific selenoamino-acids in this tissue. On the contrary, Se-yeast supplementation led to an increase in muscle Se-methionine content. We conclude that Se supplementation can increase significantly muscle Se levels and produce, particularly when Se-yeast is fed, a source of Se enriched meat as Se-methionine.     

Effect of selenium and reducing agents on in vitro immunoglobulin M synthesis by bovine lymphocytes

A series of experiments was conducted to evaluate the effects of inorganic and organic forms of Se with or without reducing agents on in vitro IgM production by bovine lymphocytes. Peripheral mononuclear cells were isolated from nonlactating Jersey cows fed a diet with adequate Se. Cells were stimulated with pokeweed mitogen and, in addition, were cultured with various Se compounds at a concentration of 100 ng Se/ml. Mercaptoethanol (50 microM) and glutathione (1 mM) were included in cultures of cells stimulated by pokeweed mitogen with and without inorganic Se. Sodium selenite was less effective than selenomethionine and selenocystine in augmenting pokeweed mitogen-induced Ig synthesis. The addition of mercaptoethanol to pokeweed mitogen-stimulated control cultures enhanced in vitro IgM production, whereas the addition of glutathione had a negligible effect, but addition of either in combination with sodium selenite dramatically depressed IgM production. These results suggest that Se in inorganic or organic forms enhances B-cell function in vitro.     

The effect of heat treatment on intrinsic and fortified selenium levels in cow's milk

The effects of two heat processing methods (pasteurisation and spray drying) routinely used in the processing of cow's milk and the production of infant formula powder on the selenium (Se) content of liquid milk, milk fortified with sodium selenite and sodium selenate were studied. Pasteurisation reduced intrinsic Se and selenate levels by 7.9% and 6.2% at p < 0.05 level and selenite levels by 7.0% at p > 0.05 level. Se losses following spray drying were 44.8% (p < 0.001), 11.4% (p < 0.01) and 10.0% (p < 0.01) for intrinsic selenium, selenite and selenate fortified milk, respectively. Total Se losses from unprocessed milk following processing (pasteurisation and spray drying) were 49.2% (p < 0.001), 17.6% (p < 0.001) and 15.6% (p < 0.001) for intrinsic selenium, selenite and selenate fortified milk, respectively.