Research Of Selenium Enrichment Characteristic And Speciation Distribution In Soybean

Selenium is an essential trace element for human health, which not only plays an antioxidant role, but also enhances the immunity of the body. It is known that one of the safest ways to get organic selenium is to supplement cultivated plants with inorganic selenium during growth. Soybeans are widely planted in China which have nutritional and economic value. In our study, Selenium enriched soybean was cultivated in experimental fields for four months in which the manure-based growth medium contained different concentrations of sodium selenite. We have studied selenium enrichment characteristic of soybean and the chemical forms of selenium. We draw the following conclusions:1, As the increasing concentration of selenium in the soil, the selenium content in the soybean show the increasing trend in the first, then slow down. The change of selenium concentration effect on the protein little. 40 mg/kg concentration of selenium in the soil is the proper content for the growth of soybean.2, The selenium content in soybeans were determined by Microwave Digestion-Graphite Furnace Atomic Absorption Spectrometry(GF-AAS). The effects of digestive reagent and digestion conditions on sample preparation were discussed and the determination conditions by GF-AAS were optimized.The sample was ingested with high-pressure closed vessel using nitric acid-hydrogen peroxide as solvent. The best Microwave Digestion procedure:(1)1 min、 0.5 Mpa;(2)2 min、 1.0 Mpa;(3) 3 min、1.5 Mpa; 3 μL 1% Ni(NO3)2 were selected as chemical modifiers to increasing the thermostability of selenium, and the pyrolysis temperature and the atomization temperature were seted at 800 ℃ and 2300 ℃, respectively. under the optionmal condition, the calibration curve showed a good linear relationship between the adsorption peak area and selenium concentration in the range of 0~250 μg/L with a detection limit of 1.20 μg/L. The relative standard deviation( n= 10) of blank sample was 3.86 % and recovery varied from 96.46 % to 103.7 %.3, The study of speciation of selenium in the soil showed that the order of selenium content in four type of extraction was:Na OH>HCl>Tris-HCl>H2O>Na Cl.. It showed that different species of selenium exist in the soil.4, We have selected Na OH、HCl、Tris-HCl、H2O、Na Cl as four type of extracts to dissolve the different forms of selenium in soybean. The result show that mostly of selenium was dissolved in Na OH, which account for about 35 % in the total selenium. The proportion of selenium in the HCl and Tris-HCl extraction were 25 % and 20 % respectively. The result show that the organic selenium is the main form in the soybean.5, According to the single factor experiments, the optimum extraction process for selenium-enriched soybean protein was determined through Box-Behnken central composite design and response surface methodology. Selenoamino acids were obtained from soluble protein under the optimized extraction conditions. Selenomethionine was qualitatively and quantitatively analyzed by liquid chromatography with mass spectrometry. The result showed that the optimal condition forextraction was: liquid/material ratio,11:1; extraction temperature, 44 ℃; extraction time, 96 min.The yield of soluble selenium-containing protein was 76.03 %. This study provides a scientific approach for soybeans to be selenium-enriched as a functional organic food. 6, Enzymatic hydrolysis was used to study the speciation of selenium in the soluble proteins of soybean. Parameters for high performance liquid chromatography-electrospray ionization tandem mass spectrometry(HPLC-ESI-MS) measurements were optimized. Se-methyselenocysteine(Se-Me Se Cys) and selenomethionine( Se-Met) were monitored by selecting the multiple reaction monitoring(MRM) mode. The results showed that inorganic selenium was absorbed by soybean and biotransformed mainly into Se-Me Se Cys. Se-Me Se Cys represented 66.4 % of the selenium in Se-protein and 29.2 % of the total selenium. HPLC-ESI-MS was proven to be a sensitive and accuracy method for the identification and quantification for the speciation of selenium in soybean. The content of Se-Me Se Cys and Se-Met were more than 113 μg/kg and 12.1 μg/kg.