| Extracellular Polysaccharide(EPSs)of lactic acid bacteria refers to the polysaccharide secreted by lactic acid bacteria in the process of growth and metabolism outside the cell and in the matrix in which it is located.Studies have found that EPSs of lactic acid bacteria has been widely used in the fields of food,pharmacy and chemical industry as bioflocculant,biosorbent,heavy metal remover,drug releasing agent,etc.In this paper,an L.plantarum NM8 strain isolated and screened from sour mare milk is used as the starting strain,and the EPSs produced by the strain is subjected to separation,purification,extraction,purity identification,primary structure analysis,secondary structure analysis,electron microscope picture analysis,and the addition of purified polysaccharide to fermented milk to measure and study its apparent viscosity by using rotational rheometer.The main research results are as follows:1.The crude polysaccharide produced by L.Plantarum NM18 is 354.90 mg/L by ethanol extraction.After decoloration,the crude polysaccharide is turned into white flocculent solid.Six components of EPS-1 A,EPS-1B,EPS-2,EPS-3,EPS-4 and EPS-5 were purified by DEAE-Cellulose 52 and Sepharose CL-6B chromatography column.2.The first-order mechanism of EPS-1B was analyzed by NMR.It was found that there was an alpha configuration and a beta configuration in EPS-1B,five sugar residues in EPS-2,four sugar residues in EPS-3,five sugar residues in EPS-5,and no obvious peaks in other components such as EPS-1A and EPS4.According to the secondary structure analysis of EPS-1B,there are six H-H bonds and one C-H bond in EPS-1B,nine H-H bonds and two C-H bonds in EPS-2,four H-H bonds and two C-H bonds in EPS-3,eight H-H bonds and three C-H bonds in EPS-4,five H-H bonds and four C-H bonds in EPS-5.3.The antioxidant activity of CEPS and EPS was determined by chemical method.The results showed that when the concentration of polysaccharides was 40 mg/ml,the combined rates of CEPS,EPS-1,EPS-2,EPS-3,EPS-4 and EPS-5 were 53.42%,35.78%,32.98%,56.78%,24.67%and 43.74%respectively,and the clearance rates were 9.56%,8.34%,7.46%,9.85%,6.45%and 8.89%,respectively.The total antioxidant activity of EPS-3 was the strongest,which was 0.167,0.154,0.142,0.176,0.134 and 0.158.4.Lactobacillus plantarum Z23 with low EPS production was used as the control group,EPS with 20.0 mg/L was added as the experimental group 1,and Lactobacillus plantarum NM18 was used as the experimental group 2 to determine its rheological properties.The results showed that the apparent viscosity of control group was 0.113 Pa.s;the apparent viscosity of fermented milk with strain NM18 as starter was 0.43 Pa.s;while the apparent viscosity of fermented milk added with EPS-1,EPS-2,EPS-3,EPS-4 and EPS-5 were 0.5434 Pa.s,0.4265 Pa.s,0.383 Pa.s,0.3475 Pa.s and 0.3208 Pa.s,respectively;the apparent viscosity of fermented milk added with extracellular polysaccharide and fermented milk added with strain NM18 was higher than that of control.The stability of fermented milk added with exopolysaccharide was better at 5??15? when EPS-1,EPS-2,EPS-4 and EPS-5 were added,the stability of fermented milk was better;when EPS-1,EPS-3,EPS-4 and EPS-5 were added at 30?,the stability of fermented milk was better;so the storage of fermented milk was better.The storage temperature should be 5?.In conclusion,the EPS produced by strain NM18 has good antioxidant activity and enhanced the viscosity of fermented milk.This paper provides a theoretical basis for the research and application of extracellular polysaccharides from Lactobacillus. |
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