Optimization And Microencapsulation Of Antioxidant Lactic Acid Bacteria In Xinjiang Traditional Cheese

Oxidative stress is a risk factor for cardiovascular diseases,chronic diseases and degenerative diseases.Antioxidant is extremely important for human body.As probiotics,the antioxidant capacity of lactic acid bacteria has been confirmed by many studies.In this thesis,161 lactic acid strains isolated and purified from cheese samples in Ili,Hami and Tacheng,Xinjiang were selected as the research object.Lactic acid bacteria with antioxidant activity were screened through antioxidant experiment and in vitro simulation experiment,identified by 16S r DNA homology analysis,optimized the culture medium,obtained the optimum culture conditions and microencapsulated the antioxidant lactic acid bacteria,Sodium alginate and chitosan were used as wall materials to encapsulate the lactic acid bacteria.The solubility of microcapsule gastrointestinal fluid was determined.At the same time,electrospinning the lactic acid bacteria fermentation supernatant with high antioxidant activity for the development of new food antioxidant activity packaging materials.The main conclusions are as follows:(1)The initial screen:Taking 161 strains of lactic acid strains in cheese samples as the research objects and 41 strains with good tolerance were obtained through hydrogen peroxide tolerance test;hydroxyl radical scavenging ability,supernatant scavenging ability,superoxide anion scavenging ability,reducing ability,metal ion chelating ability and DPPH free radical scavenging ability were measured in the fermentation supernatant,bacterial suspension and cell crushing liquid respectively.A total of 12 lactic acid bacteria with strong comprehensive ability were screened out.The results of 16S r DNA homology analysis showed that:There were 8 strains of Lactococcus,S5-7,E3-2,B5-8,S4-7,B3-3,S4-9,B2-1 and T2-10,one strains of Lactobacillus casei:S5-11;2 strains of Lactobacillus fermentum:T1-4,S2-7;one strains of Enterococcus faecalis:S4-14.(2)Tolerance of digestive fluid and optimization of culture medium:The 12 strains were subjected to artificial simulated gastrointestinal tolerance test and bile salt tolerance test.Finally 8 strains with good tolerance were obtained:S5-7,E3-2,B5-8,S4-7,B3-3,S4-9,B2-1 and T2-10.The 8 strains of lactic acid bacteria were optimized from the initial p H of the medium,culture time,culture temperature,and inoculum amount to obtain the optimal culture conditions for each strain.(3)Microcapsule production:Sodium alginate and sodium alginate chitosan microcapsules were prepared for the above 8 strains.The embedding rate was above 70%,the particle size was between 1.5 mm and 2.9 mm,the number of viable bacteria was about 10~9CFU/m L.In the continuous dissolution experiment of simulated gastrointestinal fluid,the solubility of microcapsules is between 82%and 96%.The fermentation supernatants of strains B5-8,S4-9,S5-11,and T2-10 were selected to make nanofiber membranes by electrospinning,and the DPPH free radical scavenging rate decreased by only about 10%.