Screening Of Streptococcus Thermophilus Strain With High Selenium Polysaccharide And Study On It's Fermentation Characteristics

Selenium is an important trace element of animal,plant and microbial.Since its biological function is found,the attention degree of selenium gradually is increasing.Because natural selenium content of food can not meet human needs,more and more research is committed to organic selenium-rich food,health products and medicines.Selenium polysaccharide is an organic selenium compounds with both activity of selenium and polysaccharide.The biological activity of Selenium polysaccharide is better than polysaccharide and selenium respectively.The character of easily absorbed and utilized reduce the side effects,so the research of Selenium polysaccharide is of great significance.In this paper,we use Streptococcus thermophilus S1 preservated by our lab as the original strain and subjected by ultraviolet and nitrite complex mutagenic treatment.After that we select a Streptococcus thermophilus strain with high selenium polysaccharide yield and its medium and culture conditions were optimized to determine the optimum fermentation conditions of mutant strain fermentation Selenium Polysaccharide.Finally,we use selenium polysaccharide and extracellular polysaccharide produced by fermentation of mutant strain as materials to compare the activity of anti-oxidation.1.We first Made bacterial suspension use Streptococcus thermophilus S1 saved by Laboratory then after treatment by 1mL 0.12mol/L of NaN02 and 1mL pH4.5 HAc-NaAc buffer for 15min,UV irradiation for 3min.After that we screen a strain S13,measured obtaining the polysaccharide yield and selenium content with 0.613g/L and 663?g/g,compared with the original strain,increased 0.215g/L and 241?g/g respectively.Subculture results showed intensity genetic stability.2.The S13 as the starting strain,polysaccharide and selenium content of polysaccharide production as testing index,using the single factor and orthogonal test method,to optimize the culture medium and culture conditions,the best fermentation condition is:in the case of inoculation amount of 4%,liquid volume of 100mL/250mL,speed 120r/min,lactose concentration of lOg/L,MnSO4 concentration of 0.4g/L,selenium concentrations of 30mg/L,for 30h of incubation time,incubation temperature for 42?,the initial pH of 7.Under the condition of the cultured from polysaccharide yield of 0.826g/L,selenium content in polysaccharide of 754 ug/g.3.Selenium polysaccharide and extracellular polysaccharide produced by fermentation S13 were compared to in vitro antioxidant activity test,the results show that at a concentration range within 50?500?g/mL,with the increase of solution concentration,oxidation resistance is rising,at the same time compared with thermophilic streptococcus extracellular polysaccharide,Streptococcus thermophilus selenium polysaccharide to considerably increase the clearance rate off·OH,O2-·,a significant rise in the total reducing power,indicates that organic selenium plays an important role in improving the antioxidant activity of thermophilic streptococcus extracellular polysaccharide.