| Selenium (Se) is an essential micronutrient element and has a major nutritional and biological role for living organisms. Se was discovered by chemistrist J. J. Berzelius, Sweden in 1817. It is component of the human enzyme glutathione peroxi- dase (GSH-Px). As a necessary nutritional element for organism, Se perform many important biochemical function in the body including anti- oxygenic property, improvement of immunity, prevention of human aging etc. Lack of selenium can results of cureing the keshan disease and Kashin. forthmore, nomal functions of cardiac muscle, liver and hypothyroid were affected. In nature, Se has organic and inorganic selenium two forms. Compared with organic selemium, inorganic selenium is high toxicity and low bioavailability. In recent years, organic selenium-enriched products including selenized– yeast, selenized-garlic and selenized-onion etc. Selenized-yeast is becoming increasingly popular as a food supplement for human and animals. It is attractive as a supplementary source of selenium owing to its ability to act as a precursor for selenoproteins synthesis and its high content of selenomethi- onine (SeMet), which is a highly bioavailable form and lower toxicity than inorganic selenium of Se found in most foods. Since the bioavailability and the toxicity of Se are closely correlated with its chemical form. Consequently, it is very critical that chemical forms and biochemical funtion evaluated correctely. in rencent years, many techniques for the separation, detection, determination and identification of selenocom -pounds in selenized–yeast were developed. For example, atom absorption spectrome try (AAS), atom fluorescence spectrometry (AFS), gas phase chromatography (GC), high pressure liquid chromatography (HPLC), mass sepectrum (MS).In this work, a novel comprehensive approach was developed to evaluated selenium speciation in selenium-enriched yeast. The distribution of selenium- containing proteins in the yeast was investigated by a combined technique of 2- Dimensional gel electrophoresis and synchrotron radiation X-ray fluorescence after a one step solubilized extract procedure. The small Se-containing species (Mr<5KD) in the water extract (water-soluble ) were analyzed by a hyphened technique of reversed -phase ion-pairing high performance liquid chromatography coupled with ICP–MS (RP–IP– HPLC -ICP-MS). The hyphened technique was also used for investigating the selenoaminoacid incorporated into the proteins after an enzymatic hydrolysis with pronase E (protease XIV). Selenium content in the two extracts and yeast material measured by ICP–MS. In addition, comparation between one step solubilized and sequential extraction procedures for the extraction yields of se- containing proteins and recovery of Se in Se-containing proteins. The result shows that, Selenium content in the yeat measured by ICP-MS was 1411.42±10.75μg g-1. About 157 Se-containing proteins were identified. The Se recovery of the water-soluble extract procedure (water-soluble selenium-conteining species) is 15.1%, Among them, inorganic Se species (selenite, selenate) only account for less than 0.52 %, above 99% is organic selenium in slenized-yeast by subtraction .Leaching with proteolytic enzymolysis led to a Se recovery of 81.2 %, the majority Se form in proteins was selenomethionine (SeMet), which comprised 65.26% of total selenium. One step solubilized and sequential extraction procedures for the extraction yields of seleno- proteins are 12.8% and 17.6%, respectively (yeast protein content is approxi mately 40% dry mass).A system study for selenium species in selenized-yeast in this paper, it can provide the valuable reference about further studying selenized-yeast as a selenium supplementary food.
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