| Selenium is one of the essential trace elements in human body.With the in-depth study on the function and mechanism of selenium in food,selenium-rich food has attracted more and more attention.Pleurotus ostreatus has a strong ability to enrich selenium.With liquid fermentation and culture technology,organic selenium,such as selenium protein and selenium polysaccharide can be extracted,and can be used as effective components in health drinks.In this thesis,Pleurotus ostreatus strains suitable for selenium-rich culture were screened for optimizing the fermentation conditions of selenium-rich liquid.The formula composition of selenium-rich drinks was explored,which provided a reference basis for the development of selenium-rich food.Specific research contents are as follows:(1)Screening of Pleurotus ostreatus strains and optimization of fermentation conditions in selenium-rich liquid.Six media with sodium selenite gradient concentration were designed to measure the colony diameters of 10 different kinds of Pleurotus ostreatus strains at different concentrations every 24 h.Then the average daily increase of diameters were calculated for selecting the optimal selenium-rich strains in combination with sensory evaluation,which were used in the optimization experiment of selenium-rich liquid culture.The dry weight of mycelia was taken as the index.The single factor and orthogonal experiment were carried out on the three main influencing factors of sodium selenite mass concentration,p H value and shaker speed.RESULTS: Pleurotus djamor P043 had the best growth under different concentrations,and the average daily growth of colony diameter reached 17.83 mm when the concentration was 8.0 mg/L.The optimal conditions for culture in selenium-enriched liquid were as follows: mass concentration of sodium selenite 7.5 mg/L,p H 7.0 and speed 200 r/min.(2)Determination of selenium content,total sugar content,selenium polysaccharide content and antioxidant capacity of Pleurotus djamor P043 under optimal conditions of liquid fermentation with selenium enrichment.RESULTS: The organic selenium content and total sugar content of hyphae cultured in liquid selenium group were 22.24 mg/kg and 88.60 g/100 g,which was significantly higher in Se-enriched group than that in Se-free group(P<0.05).Ultrasound-assisted enzymatic extraction and determination of selenium polysaccharide content of 5.36%.The total antioxidant capacity of selenium polysaccharide was between that of common polysaccharide and Vc,which indicated that selenium polysaccharide had good antioxidant capacity.(3)Optimization of selenium polysaccharide drink formula.Using P043selenium-rich polysaccharide lyophilized powder as the main material,adding clarifying agent,correcting agent and preservative as auxiliary materials,the single factor and orthogonal tests of the ratio of the main and auxiliary materials were conducted.To clarify degrees,selenium polysaccharide content and total antioxidant composite scores,in combination with sensory evaluation,get the best formula: solid-liquid ratio 1:30,6%clarifying agen,2%Xylitol,0.05% Citri Acid Anhydrous,0.3% potassium sorbate.After filling and sterilization,the finished product(10 m L/piece)was obtained.Microbial limit,physical and chemical index were determined in accordance with the national food standard.Se content in drink was 3.15 ?g/piece.(4)Pleurotus djamor P043 is suitable for Se-enriched culture and has good Se-enriched ability and polysaccharide conversion ability.Under the optimal liquid culture conditions,Se-enriched products with antioxidant ability superior to common hyphae can be obtained to the greatest extent,and can be used as food raw materials for processing.By optimizing the formula of selenium polysaccharide drink,functional selenium rich food with both selenium and antioxidant ability was prepared. |
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