| Selenium (Se) is an essential nutrient in the human diet and metabolism. Selenium deficiency may lead to heart disease, hypothyroidism and immune malfunction. In recent years, Se compounds have been internationally recognized to have the ability of anti-cancer. The average total human Se intake in China, as reported by the Chinese Nutrition Association, is only 26μg/d, and this is substantially lower than Chinese Preventive Medicine Center's recommended intake of 50-240μg/d. Epidemiological studies indicate if adults are supplemented with 200μg/d selenium, the cancer morbidity and mortality may reduce about 50%. Different sources and the chemical form of selenium compounds have different safety and biological functionality levels. Se of plant origin is mainly in the form of selenium amino acids that have higher bioavailability and will not easily cause toxic accumulation in the human body. Therefore, the use of vegetable as a vector of organic selenium enrichment is a appropriate choice. This thesis studied the Selenium bioconversion in vegetables, the formation mechanism of organic selenium, and the processing effects of selenium enriched. The results can provide the basic knowledge for application and the guidance in the industrialization of functional food containing this trace elements.First, flowering Chinese cabbage (Brassica campestris L. ssp. Chinensis (L.), cabbage (Brassica oleracea var. capitata L.) edamame(Glycine Max (L.) Merrill.) and asparagus (Asparagus officinalis L.) were selected as the selenium enrichment test materials for studying inorganic selenium uptake and transfer pattern in vegetables and effects of selenium treatment on nutritional ingredients for the vegetables. The results show that selenium was a transportable and recyclable element in vegetables. Within certain ranges of spraying concentration, selenium content enriched was linearly correlated with the concentration of NaSeO32-. Twice spraying with lower concentration of NaSeO32- and adequate adjustment of pH improved selenium absorption in vegetables. Spraying of selenium on cabbage at a later growth phase led to higher selenium accumulation in vegetables. Selenium treatment with appropriate concentrations increased protein, vitamin C and chlorophyll synthesis, whereas decreased soluble sugar content. Selenium enrichment did not change the amino acid type and distribution, However, the molecular weight distribution tests and electrophoresis showed that high molecular weight protein in edamame (100kDa) decreased, whereas medium and small molecular weight protein increased. Selenium enriched edamame had a decreased oil content, in which unsaturated fatty acids rate reduced and saturated fatty acids rate increased.Second, selenium component extraction method and speciation were studied. Through HCl buffer and ultrasound-assisted extraction method, selenium component in cabbage and soybean can be extracted. Results show that the main selenium form in cabbage is in free state, and main selenium form in edamame is protein binding. Using 0.01 HCl buffer, assisted with 120 sec ultrasonic probe, most selenium in cabbage can be extracted. For edamame selenium extraction, it is necessary to adopt proteolytic processing. Ultrasound can be used to deal with selenium soybean protein to shorten the enzyme process to 180s. Derivative of selenium amino acid in cabbage and edamame was done with ethyl chloride formate. Then, they were detected with gas chromatography mass mass spectrometry. Chemical analysis of selenium showed that main selenium species in cabbage was Se-methyl-selenocysteine although selenomethionine and selenocystein were also detected. For edamame, the main selenium species was selenomethionine.Further, effect of the cabbage and soybean juice process and the dehydrate process on selenium content were studied. When fresh cabbage and edamame were stored under 4℃for 4 weeks,the selenium degradation rate in cabbage was up to 30-45% and soybean selenium was relatively stable, with a degradation rate at about 10%. Blanching and seasoning could reduce the browning degree, and maintain the green color. But blanching process caused the loss of selenium in cabbage at about 20-30%. Edamame selenium was more stable than cabbage during the dehydrated processing. Comparing different dehydration process, freeze-drying had the highest preservation rate for organic selenium. Selenomethionine is a heat-labile component, and the spray drying process resulted in the highest loss of selenomethionine. Met-Secysteine had a certain extent loss even in the freeze-drying process. In the drying process, temperature and time were the most significant factors for the degradation of selenium but the latter had even greater impact . Fitting equation is Y=1.24321-0.00276X1-0.00075X2 (X1 is temperature , X2 is time). Se degradation agreed with a dynamic model of the Boltzmann equation: with the apparent activation energy (Ea) of 44,027 J/mol.Finally, the extrac of selenium cabbage was used to study in-vitro antitumor activity and the antidiabetic mechanisms in type II diabetic mice. A long-term intake of selenium enriched products for mice was done to study the antioxidant enzymes and physiological and biochemical indicators. Cytotoxic bioactivity study on H446 cell line showed that selenium extract had stronger inhibition in vitro. The cell morphology sticked to the bottle wall showed bigger change and the sum of cells was decreased distinctly than the control treated under microscope. The higher concentration the samples had, the more obvious phenomenon of cell apoptosis was. Selenium cabbage extract had no significant effect on normal mice, but could reduce blood glucose levels in diabetic mice. After gastric perfusion of selenium, mice index of SOD, GSH-Px increased and MDA reduced, blood physiological and biochemical indicators of the control group of mice and selenium-enriched group had no significant difference. Teratogenic toxicity and genetic toxicity of selenium enriched juice showed that selenium vegetable products were safe and reliable to be used as functional food.
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