Screening Of Probiotic Lactic Acid Bacteria Producing Extracellular Polysaccharide And Extracellular Polysaccharide Application

Probiotics are defined as the general term for beneficial microorganisms that can reach and colonize specific sites in the gastrointestinal tract of the body in a living state.As a representative of probiotics,lactic acid bacteria have probiotic and functional characteristics,and are an important branch of the probiotic family.The study of the probiotic characteristics of lactic acid bacteria is an indispensable research method for screening lactic acid bacteria with specific functions.Lactic acid bacteria are generally recognized as food-grade microorganisms,and their metabolites during growth and reproduction,such as:lactic acid bacteria extracellular polysaccharides,bacteriocins,organic acids,etc.,have attracted widespread attention.Extracellular polysaccharide is a general term for a group of high-molecular polymers that can be separated by some microorganisms during cell growth and metabolism and secreted out of the cell wall and penetrate into the culture.The extracellular polysaccharides of lactic acid bacteria have unique physical and chemical properties and biological activities,which has opened up research directions for the development of functional microbial resources.A large number of studies have shown that lactic acid bacteria extracellular polysaccharides are used as thickeners,emulsifiers,gelling agents,etc.in the food industry to improve the rheological properties,texture and mouthfeel of foods.In this study,strains with better probiotic properties were selected from the lactic acid bacteria isolated and stored in our laboratory,from which the screening and identification of extracellular polysaccharide-producing lactic acid bacteria,the isolation and purification of extracellular polysaccharides,physical and chemical properties,and extracellular polysaccharides in fermented milk Systematic research.The main findings are as follows:(1)Screening of lactic acid bacteria and research on probiotic characteristics.In this paper,we first selected 100 strains of fresh milk samples from the main mountain pastures in Hunan(including Nanshan pasture,Wangcheng and Ningxiang,etc.),and passed the acid and bile salt tolerance test(p H=2,3.0 g/L cattle Bile salt)9 strains of lactic acid bacteria(NS1904E,NS1905E,NS1911E,NS1912E,NS1924E,NS1928E,NS1932E,NS1937E,NS1938E)were selected to grow and reproduce in special environments.Using the strain LGG as a control,it was found that 5 strains of lactic acid bacteria(NS1904E,NS1905E,NS1912E,NS1924E,NS1932E)had better survival ability through simulated gastrointestinal juice experiment and aggregation ability experiment.The above 5 strains of lactic acid bacteria were tested for adhesion ability and all showed good adhesion ability,of which the strain NS1904E had the highest adhesion ability,up to(67.89±2.91 CFU/cell).After safety evaluation,all strains were preliminarily determined to be safe.(2)Screening and identification of extracellular polysaccharide-producing lactic acid bacteria and study of extracellular polysaccharides.Combining the colony drawing method with the quantitative determination of EPS,the strain NS1905E was determined to have the highest sugar yield,reaching 561.16±19.98 mg/L,and the strain was identified as Lactobacillus plantarum;Lactobacillus plantarum NS1905E was fermented,centrifuged,Ethanol precipitation,protein removal,dialysis,freeze-drying to obtain preliminary purified polysaccharide(L.plantarum NS1905E-EPS);physical and chemical molecular characterization of L.plantarum NS1905E-EPS:component analysis results showed that the protein content was 1.35±0.03%,total sugar The content is 84.44±0.01%,the ash content is 1.31±0.68%,the moisture content is 9.51±0.83%;the polysaccharide in the water phase is measured by gel permeation chromatography(GPC)and multi-angle laser light scattering(MALLS)The weight average molecular weight(Mw)is 2.658×10⁵Da;the analysis of monosaccharide composition shows that:glucose:arabinose:rhamnose:mannose:galactose=58.83:17.4:6.31:5.86:2.74;the average particle size is 191.9nm;L.plantarum NS1905E-EPS aqueous solution(0.1%w/w)of the original solution(p H=4.08)-19.43±0.59 m V,indicating that the polysaccharide is acidic anionic polysaccharide;scanning electron microscope(SEM)observation found that L.p lantarum NS1905E-EPS presents a fast structure with different sizes and smooth surfaces;AFM observed L.plantarum NS1905E-EPS in the form of chain polymers of varying lengths and different heights in aqueous solution,indicating L.plantarum NS1905E-EPS has gathered.Rheological characteristics analysis found that the L.plantarum NS1905E-EPS is a pseudoplastic fluid,which has good temperature tolerance in the range of-20?90?;it is not greatly affected by salt ions such as Ca²⁺,Na⁺,Mg²⁺;K⁺It will destroy the structure of polysaccharides;it has good resistance to acid and alkali in the p H range of 2 to 14,and the damage of strong base to its structure is stronger than strong acid.(3)The application of L.plantarum NS1905E extracellular polysaccharide in fermented milk was studied.By adding different concentrations of L.plantarum NS1905E-EPS to fermented milk,the effects on fermented milk quality,rheological properties and the stability of fermented milk during storage were studied.With no addition of L.plantarum NS1905E-EPS as a control,when the amount of L.plantarum NS1905E-EPS added increased to 0.1%,the viscosity increased from 1263.35 m Pa.s to 2115.14 m Pa.s;the water holding capacity increased from 52.01±4.09%to 57.15±0.91%;indicating that the addition of L.plantarum NS1905E-EPS can significantly improve the quality of fermented milk;analysis of the number of live bacteria in fermented milk shows that L.plantarum NS1905E-EPS can promote the growth of S.thermophilus during the fermentation process.The impact of bulgaricus is not significant;with the increase of L.plantarum NS1905E-EPS,the fermented milk shows better elasticity;during the storage of fermented milk,the fermented milk G'and G''show an increase and then decrease.The highest G'and G''values are shown on the 7th day of storage,...