Preliminary Study On Screening/identification,Applications Of Expolysaccharide And Fermentation Technology Of Expolysaccharide-producing Lactobacillus

Lactobacillus plantarum is a type of multifunctional lactic acid bacteria,which can be used as a food starter.Its metabolites contain a variety of biologically active substances,among which extracellular polysaccharide(EPS)has great application value and development potential.Studies have found that EPS has probiotic functions such as anti-oxidation,anti-tumor,and immune regulation.In this thesis,we aim at isolating the EPS hyper-production Lactobacillus plantarum strain from kimchi,carrying out scale-up cultivation and EPS production quantification,characterizing and analyzing the monosaccharide composition and morphology structure of the produced EPS,applying the EPS in the biosynthesis of selenium nanomaterials and the methylene blue(MB)adsorption.The main findings are as follows:(1)Lactobacillus plantarum R040 with high EPS yield was isolated from Fuyuan Kimchi.In shaking flask test,when Lactobacillus plantarum R040 was cultured at 31?,pH 6,and initial inoculation of 3%for 18 h,the yield of EPS-R040 was the highest,which reached1.8 g×L^-1.Further we carry out the scale-up/mass production research of EPS-R040 in a 5L fermentor.In fed-batch fermentation,the maximum output of EPS-R040 was 2.27 g×L^-1;Biocatalytic,the output of EPS-R040 reached 3.34 g×L^-1 at the 9th hour,which has been greatly improved,and cost savings,improve production efficiency.(2)EPS-R040 shows a rough porous network structure with pores or holes.It is composed of galactose,glucose,mannose and glucuronic acid,with a molar ratio of1.4(25)9.4(25)3.4(25)1.0.Moreover,EPS-R040 is not a homogeneous polysaccharide,but a mixture of sugars with different relative molecular masses(1.8x10⁴,1.9x10⁶Da).(3)E-SeNPs with good dispersibility and stability were successfully prepared by using EPS-R040 as reducing and stabilizing agent.The average particle size of the prepared E-SeNPs is 45.17±11.9 nm,with a negative charge(-31.3m V).Meanwhile,the E-SeNPs can be stable in the aqueous solution for 20 days.It was found by FT-IR analysis that the stability was due to the coating effect of EPS-R040.Finally,at the same concentration,the reducing power and ABTS⁺radical scavenging rate of E-SeNPs were significantly higher than those of EPS-R040 and selenium nanoparticles(SeNPs).(4)The adsorption capacity of EPS-R040 toward MB is affected by contact time,temperature,initial MB content and pH.Its maximum adsorption capacity is 1853.0 mg×g^-1.Moreover,EPS-R040 also exhibits excellent desorption capacity,which can be recycled three times with little loss of adsorption capacity.The experimental results show that hydrogen bonding is the main adsorption mechanism of MB.EPS-R040 can not only synthesize selenium nanoparticles with good stability,but also has excellent adsorption performance.The results of this paper provide an important reference and knowledge reserve for the potential application of EPS-R040 in synthetic materials and solving water pollution.