Characterization Of Exopolysaccharide Produced By Lactobacillus Plantarum KX041 And Strain Probiotic Properties Analysis Along With Applications

Exopolysaccharides(abbreviated as EPS in this paper)are important metabolites of Lactic acid bacteria.They can be secreted to the external environment in the form of slime EPS or adhere to the bacterial surface forming capsular EPS.EPS have been usually used as natural and safe thickeners,emulsifiers or stabilizers to improve food texture.In addition,EPS also possess several functional characteristics,such as antioxidant,anticancer,immune modulatory,antibacterial,hypoglycemic,antihypertensive,cholesterol-lowing activities and the ability of promoting the colonization of probiotics in the intestine of host.Lactobacillus plantarum KX041 was screened from pickle(Kaixian,Chongqing).Our previous studies showed that this strain could produce EPS with strong antioxidant capacity and also produce bacteriocins with good bacteriostatic ability,indicating that this strain has a good utilization value.In this paper,the EPS was further decolorized and purified.The structures and functions of the purified EPS fractions were studied.In addition,the probiotic properties of L.plantarum KX041 and fermentability of the strain in the skim milk and soybean milk were researched.Results are as follows:(1)The technical parameters for decolorization of EPS from L.plantarum KX041 by macroporous resin were explored.In addition,effects of decolorization process on polysaccharide content,molecular weight distribution,monosaccharide composition and FTIR spectrum were studied.Furthermore,immune regulation,anti-tumor and antioxidant properties of decolored EPS were also analyzed.The results showed that macroporous resin D4020 provided optimal decolorization of EPS.The optimum conditions for static decolorization of resin D4020 were as follows: the amount of D4020 macroporous resin was 3 g/20 mL,sample concentration was 5 mg/mL,and decolorization time was 5 h.The decolorization rate was 81.2%,and the polysaccharide retention rate was 69.77%.Moreover,some protein and EPS fraction with smaller molecular weight were also absorbed by macroporous resin D4020,increasing the content of sugar.The protein content of EPS decreased from 9.4% to 0.4%,and the polysaccharide content increased from 46.17% to 80.04%.The type of monosaccharides has not changed,but the proportion has changed.In addition,the result showed that decolored EPS behaved shear-thinning patterns with its increasing concentration and exhibited flocculation and emulsifying abilities.Furthermore,it could also promote the proliferation of RAW264.7 macrophages and neutral red phagocytosis.What's more,EPS had DPPH/ABTS radicals scavenging activities.(2)The further purifications were conducted to obtain EPS fractions,which were called as EPS-1-1,EPS-2-1 and EPS-3.Their structures and conformational characterizations were determined through FT-IR,UV,GC,HPLC,NMR,SEM and Congo red test analysis.The Mw of EPS-1-1,EPS-2-1 and EPS-3 were estimated to be 57201,70734,and 26387 Da,respectively.EPS-1-1 and EPS-2-1 had the similar structure,composed of arabinose,mannose,glucose and galactose with a ratio of 1.09:88.53:3.99:6.39 and 0.58:94.11:3.55:1.76,respectively and were both ?-type configurations.Whereas,EPS-3 contained rhamnose,fucose,arabinose,xylose,mannose,glucose,galactose and galacturonic acid in a molar ratio of 2.01:2.65:10.95:4.62:4.07:27.81:44.16:3.73 and possessed a triple helical structure.SEM results indicated EPS-1-1 and EPS-2-1 appeared flake shapes piling up into compact structures with a rough surface.In addition,these purified EPS fractions all possessed the immune activity,DPPH/ABTS radicals scavenging activities and plasmid DNA damage protective effect.(3)L.plantarum KX041 was able to resistance to high osmotic pressure(8 % NaCl),pH 2.0 and 0.25% cholate environment,indicating it could survive in human gastrointestinal tract.The strain was proved to have good surface hydrophobic ability,demonstrating that it had a good adhesion ability to intestinal epithelial cells.At the same time,it was also proved that the cell suspension had DPPH/ABTS,hydroxyl radicals scavenging activities and reducing capacity.L.plantarum KX041 had poor fermentability in the skim milk,but it could be used as an adjunct culture,and had no adverse effects on the texture,acidity and flavor of yogurt.During 21 days of cold storage,it could maintain the bacteria activity,and the postacidification ability was weak.L.plantarum KX041 had better fermentability in the soymilk,and it could be used as a single starter in fermented soymilk.The soya-yogurt fermented by strain KX041 had better texture characteristics and water hold capacity than one fermented by commercial bacteria.The reason may be related to the rate of acid production and the produced EPS.At the same time,the soya-yogurt fermented by L.plantarum KX041 maintained stable bacterial activity and had a weak post-acidification ability during cold storage period,so it could be used as a good starter culture in soya-yogurt.