Selenium enriched edible plants

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1 Selenium enriched edible plants Krystyna Pyrzynska University of Warsaw, Department of Chemistry, Poland Abstract Selenium is an important element from environmental and biological point of view In the world, deficiency of Se in a diet is more common and nutritional supplements have been recommended. The ability of several plants to accumulate and transform inorganic selenium forms into bioactive its organic compounds has important implications for human nutrition and health.. This work gives a brief overview of the studies carried out to characterize selenium species produced by different enriched edible plants which were grown in the presence of different Se species. Keywords Selenium species; enriched edible plants; selenium accumulation and transformation Introduction Selenium (Se) is one of the minor but biologically essential element for humans and animals, needed for the activity of anhtioxidative enzymes, such as glutathione peroxidise and thioredoxin reductase [1]. In addition, several studies have suggested that its optimal status could protect against oxidative stress and prevent cancer and cardiovascular disease [2, 3]. Recommended Se dietary intake is not standardised among different countries. The recommended dietary allowance (RDA) for Se in the USA is 55 μg/day for men and women, while the WHO recommends a intake of 40 and 30 μg/day for men and women, respectively. Selenium intake, especially in southern and eastern European countries, is below the RDA level [4]. Thus, consumption of Se supplements has been the most widespread approach to prevent its deficiency. Selenized yeast (generally, Saccharomyces cerevisiae) is used as a main source of selenium in most food supplements. Yeast grown in a broth containing inorganic selenium incorporates the selenium in place of sulfur in amino acids, such as methionine and cysteine. Selenomethionine (SeMet) has been found to be the major form in selenized yeast [5,6]. This form of selenium has been found to be more bioavailable and less toxic than inorganic selenium species (selenite or selenate). The ability of SeMet to be incorporated into the body proteins in place of methionine furthermore provides a means of reversible selenium storage in organs and tissues. This property is not shared by any other naturally occurring selenoamino acid and thus could be associated with a specific physiological function of SeMet. Several authors have reported preparation of Se-enriched foods by means of fermentation processes [7-9]. The proposed products - selenized white wine [8] or sauerkraut [9] - could become a dietary source of bioavailable and physiologically relevant selenium forms. Diet is the major source of selenium for the general population and its intake depends on the kind and amount of food consumed and the Se concentration in food products. The main source of selenium intake in some courtiers is different [10-13]. For example in Spain meat and fishes participate to a great extent, while in Egypt 70% of total dietary selenium is provided by bread (Fig. 1). Evaluation of the relationship between serum total selenium Greek adults with their major food groups and beverages revealed that serum selenium was positively correlated with the consumption of red meat, while the consumption of other selenium-containing foods (i.e. fish, cereals, dairy products, vegetables) did not demonstrate such a relationship [13]. Moreover, principal component analysis revealed that the adoption of a vegetarian type of diet is inversely correlated with total selenium.

2 Spain Bread stuffs; Meat; Fishes; Fruits and vegetables; Dairy products; Others Figure 1. Participation of different foods in daily intake of selenium. Based on [10-12]. Selenium occurs in foods through uptake by plants from the soil, in the form of the selenoamino acids, thereby entering the food chain. The Se content in plants is highly dependent on the amount of Se in the soil, which varies from country to country as well as from region to region. Selenium in soils is mainly present in inorganic forms as selenides, selenites and selenates. The distribution of these species depends on soil properties such as acidity, oxidizing conditions, the mineral and organic matter contents and the microbiological activity. Selenates dominate in the water-soluble extracts of soil. The ability of several plants to accumulate and transform inorganic forms of selenium into bioactive organic compounds has important implications for human nutrition and health [14,15]. Some plants when grown in selenium-rich soils may accumulate large amounts of selenium (up to thousands of mg/kg dry mass) without showing symptoms to toxicity and they could be applied for phytoremediation of polluted soils [16]. A member of the Brassicaceae family, Indian mustard (Brassica juncea) is one of the most studied plants in terms of selenium accumulation because of its fast growing cycle and high biomass [17]. The resistance to excessive Se has been related to the formation of selenium organic compounds that cannot be incorporated into proteins and also the ability of these plants to convert selenium into volatile species. An ideal nutritional supplement would be a selenium-enriched edible plant part wherein the selenium metabolically accumulates in the form of bioavailable organic selenium compounds. In the regions where the content of selenium in soil is low the use of Se-enriched fertilizers, spraying the crops with selenium salts or treatment the seeds with aqueous selenium inorganic salts is recommended in order to supply the population with sufficient selenium content. Plants that are consumed everywhere and naturally contain higher levels of the sulfurcontaining amino acids are preferred for enrichment, based on metabolic criteria. In this context, the present paper aims to provide an overview of the production of Se-enriched plants and distribution of selenium species. Selenium uptake by plants Selenium content in the growth mixture as well as time of exposition generally resulted in proportional increases of the Se content in plants [18,19]. Several authors have reported that different plants grown in Seenriched environment did not apparently exhibit the symptoms of toxicity [18-20]. However, the growth of onion roots was inhibited with respect to the control plants; the more pronounced effect was observed in the presence of [21]. The uptake of selenium by plants is highly dependent on its chemical form present in the growth medium (Table 1). Fortification with selenate resulted with higher accumulation of Se compared with selenite. This could be attributed to the fact that species are more available in soil. The transportation of selenium from root to shoot in plants is also highly dependent on its form of supplementation. is much more easily transported than Se(IV) using the sulfate path through the plants. Se(IV) is rapidly converted to organic forms such as SeMet, which is retained in the roots. Thus, total selenium content in onion leaves was much higher than in the bulbs [21]. Similar results were obtained for broccoli [19], red cabbage [20] and lentil [23].

3 Table 1: Examples of Se uptake by different plants Plant Treatment Total Se μg/g Ref. Kale (Brassica oleracea var. Hydroponically, 5-45 mg/l as Se(IV) Alboblabra L.) Broccoli (Brassica oleracea) Hydroponically, 1 mg/l as Se(IV) Red cabbage (Brassica oleracea Fertilization, 0.5 mg/l as Se(IV) var. capitata L. F. rubra) Onion bulbs (Allium cepa) Hydroponically, 5 mg/l as Se(IV) Potatoes Solanum tuberosum L.) Foliar spray, 10 mg/l as Lentil (Lens esculenta) Chives (Allium schoenoprasum) Buckwheat sprouts (Fagopyrum esculentum) Hydroponically, 1 mg/l as Se(IV) Se(IV) Fertilization, 10 mg Se/L as Se(IV) Soaking seeds, 20 mg/l as Se(IV) Selenium content in some edible sprouts grown in the same Se-enriched media increased in the order: lentil (98 μg/g) < alfalfa (132 μg/g) < soy (158 μg/g) [26]. Lentil sprouts contained the highest natural selenium concentration of 2.4 μg/g. These plants can be grown in hydroponic media containing inorganic selenium at up to 2 mg Se/L without there being signs of damage or growth inhibition in the plants [26]. Selenium species in plants Estimation of diets for selenium adequacy requires information not only on its total content but also on the amount of Se species accessible in a given sample. It should be mentioned that the results of selenium speciation in plants are strongly depended on the extraction conditions employed. Typical pretreatments for low molecular weight compounds involved hot water extraction (100 0 C, 1-2 h) or enzymatic digestion with protease, proteinase or driselase at room temperature for h. The use of proteolytic enzymes ensured liberation of Se species contained in peptides or proteins. In the case of enzymatic extraction the ph of the leaching solution and temperature should be maintained in the preferred range for the specific enzyme being used. Literature data show that the distribution of this element among its species is remarkably different depending on the selenium media used for plant treatment [20,23-25]. Fig. 2 presents as an example, the distribution of selenium species in Se-enriched green onions (Allium fistulosum) treated with Se(IV) and salts [24]. 90% of the total selenium content in this plant enriched with became available due to the proteolytic digestion. About 60% was present as selenate and 30% was metabolized into selenoamino acids. The organic compounds included selenocystine (SeCys 2 ) and Se-methyl selenocysteine (MeSeCys). When Se(IV) was applied as enrichment medium, the identified species of the plant were exclusively organic species. The main compound was MeSeCys Treatment with Treatment with Se(IV) SeCys 2 Uknown MeSeCys Residue Residue Uknown MeSeCys SeMet Figure 2. Distribution of selenium species in enriched green onion after proteolytic digestion. Based on [24]. However, accurate determination of selenium compounds in edible plants is not straightforward due to the low concentration of Se in samples and low extraction efficiency. Moreover, during extraction, liberated matrix components can react with extracted selenium species. The results obtained for buckwheat seeds showed a decrease

4 in Se(IV) response during sample preparation (24 h incubation at 37 o C) and storage 4 days at 4 o C), comparable to the one obtained with the experiments performed in the presence of tannin and rutin as the most common phenolic substances in plant parts [29]. Conclusion Se-enriched edible plants represents an important source of this element in the human diet. Allium and Brassica plants such as onion or cabbage are consumed everywhere and sufficient enrichment of these plants with selenium could provide a good source of supplementation, using them as seasoning in our diet. An adequate dietary intake of selenium would not necessarily mean that human body could absorb the whole amount ingested. During ingestion, food components are exposed to different conditions (e.g., change in ph between the gastric and the intestinal track), which may affect the distribution of initial species. Another topic is the stability and distribution of selenium species after different food treatments such as cooking, drying or heating. It could be interesting to know whether these plants can be consumed raw in a fresh salad or cooked in the soups. References 1. Behne, D., Alber, D., and Kyriakopoulos, A., Long-term selenium supplementation of humans: Selenium status and relationships between selenium concentrations in skeletal muscle and indicator materials. Journal of Trace Elements in Medicine and Biology, 24, Navarro-Alarcon, M., and Cabrera-Vique, C., Selenium in food and the human body: A review. Science of the Total Environment, 400, Rayman, M. P, Selenium in cancer prevention: A review of the evidence and mechanism of action. Proceedings of the Nutrition Society, 64, Rayman, M. P., Food-chain selenium and human health: Emphasis on intake. British Journal of Nutrition, 100, Połatajko, A., Śliwka-Kaszyńska, M., Dernovics, M., Ruzik, R., Encinar, J. R., and Szpunar, J., A systematic approach to selenium speciation in selenized yeast. Journal of Analytical Atomic Spectrometry, 19, Bierła, K., Szpunar, J., Yiannikouris, A., and Lobinski, R., Comprehensive speciation of selenium in selenium-rich yeast. Trends in Analytical Chemistry 41, Alzate, A., Fernández-Fernández, A., Pérez-Conde, C., Gutiérrez, A. M., and Cámara, C., 2008). Comparison of biotransformation of inorganic selenium by Lactobacillus and Saccharomyces in lactic fermentation process of yogurt and kefir. Journal of Agricultural and Food Chemistry, 56, Pérez-Corona, M. T., Sánchez-Martínez, M., Valderrama, M. J., Rodríguez, M. E., Cámara, C., and Madrid, Y., 2011). Se biotransformation by Saccharomyces cerevisiae and S. bayanus during white wine manufacture: Labscale experiments. Food Chemistry, 124, Peńas, E., Martinez-Villaluenga, C., Frias, J., Sánchez-Martínez, M.J., Pérez-Corona, M.T., Madrid, Y., Cámara, C., and Vidal-Valverde, C., Se improves indole glucosinolate hydrolysis content, Se-methylselenocysteine content, antioxidant capacity and potential anti-inflammatory properties of sauerkraut. Food Chemistry, 132, Barclay M.N., Macpherson A., and Dixon J., Selenium content of a range of UK food, Journal of Food Composition and Analysis, 8, Hussein L., and Bruggeman J., Selenium analysis of selected Egyptian foods and estimated daily intakes among a population grow, Food Chemistry, 65, Diaz-Alarcon J.P., Navarro-Alarcon M., Lopez-Gade la Serrano H., and Lopez-Martinez M.C., Determination of selenium in meat products by HG AAS; selenium levels in meat, organ meats and sausages in Spain, Journal of Agriculture and Food Chemistry, 44, Letsiou, S., Nomikos, T., Panagiottakos, D., Pergantis, S.A., Fragopoulou, E., Antootonopoulou, S., Pitsavos, C., and Stefanadis, C, Dietary habits of Greek adults and serum total selenium concentration: the ATTICA study. European Journal of Nutrition, 49, Zayed, A., Lytle, C. M., and Terry, N., Accumulation and volatilization of different chemical species of selenium by plants. Planta, 206, Ellis, R. D., and Salt, E. D., Plants, selenium and human health. Current Opinion in Plant Biology, 6,

5 16. Terry, N., Zayed, A. M., de Souza, M. P., and Tarun, A. S., Selenium in higher plants. Annual Review of Plant Physiology and Plant Molecular Biology, 51, Mounicou, S., Shah, M., Meija, J., Caruso, J. A., Vonderheide, A. P., and Shann, J., Localization and speciation of selenium and mercury in Brassica juncea Implication for Se Hg antagonism. Journal of Analytical Atomic Spectrometry, 21, Maneetong, S., Chookhampeaeng, S., Chantiratikul, A., Chinrasti, O., Thosakham, W., Sittipout, R. And Chantiratikul, P., Hydroponic cultivation of selenium-enriched kale (Brassica oleracea var. Alboblabra L.) seedling and speciation of selenium with HPLC-MS. Microchmical Journal, 108, Pedrero, Z., Elvira, D., Camara, C., and Madrid, Y., Selenium transformation studies during Broccoli (Brassica oleracea) growing process by liquid chromatography inductively coupled plasma mass spectrometry. Analytica Chimica Acta, 596, Mechora, S., Germ, M., and Stibilj, V Selenium compounds in selenium-enriched cabbage. Pure and Applied Chemistry 84, Wrobel, K., Wrobel, K., Kannamkumarath, S.S., Caruso, J.A., Wysocka, I.A., Bulska, E., Światek, J., and Wierzbicka, M., HPLC-ICP-MS speciation of selenium in enriched onion leaves a potential dietary source of Se-methylselenocysteine. Food Chemistry, 86, Cuderman, P., Kreft, I., Germ, I., Kovaĉeviĉ, M., and Stibili, V., Selenium species in selenium-enriched and drought-exposed potatoes. Journal of Agricultural and Food Chemistry, 56, Pedrero, Z., Encinar, J.R., Madrid, Y., and Camara, C., Identification of selenium species in seleniumenriched Lens esculenta plants by using two-dimensional liquid chromatography-inductively coupled plasma mass spectrometry and [ 77 Se]selenomethionine selenium oxide spikes. Journal of Chromatography A, 1139, Kapolna, E., and Fodor, P., Bioavailability of selenium from selenium-enriched green onions (Allium fistulosum) and chivs (Allium schoenoprasum) after in vitro gastrointestinal digestion. International Journal of Food Science and Nutrition, 58, Cuderman, P., Ožbolt, L., Kreft, I., and Stibilj, V., Extraction of Se species in buckwheat sprouts grown from seeds soaked in various Se solutions. Food Chemistry, 123, Funes-Collado, V., Morell-Garcia, A., Rubio, R., and Lopez-Sanchez, J.F., Study of selenocompounds from selenium-enriched culture of edible sprouts. Food Chemistry 141, Pyrzynska, K., Selenium speciation in enriched vegetables. Food Chemistry, 114, Thirty, C., Ruttens, A., De Temmerman, L., Schneider, Y.J., and Pussemier, L., Current knowledge in species-related bioavailability of selenium in food. Food Chemistry, 130, Cuderman, P., and Stibilj, V., Stability of Se species in plant extracts rich in phenolic substances. Analytical and Bioanalytical Chemistry, 396,

Selenium and its speciation in plant and animal. Vekoslava Stibilj Ana Jerše Ana Kroflič

Selenium and its speciation in plant and animal Vekoslava Stibilj Ana Jerše Ana Kroflič Selenium properties Discovered in 1817 by Berzelius and Gaham 4 oxidation states & numerous compounds selenide Se