Effect Of Exopolysaccharides Produced By Lactobacillus On Rheological Properties Of Fermented Milk

In this paper,32 strains of lactic acid bacteria isolated from traditional fermented milk in Xilingol League of Inner Mongolia were used as experimental strains.Through determination of hydrophobicity and auto-aggregation,strains with potential adhesion abilities were screened out.And the high yield exopolysaccharides(EPS)strains were furtherly screened out through Phenol-sulfuric acid method.The types of EPS produced by strains were observed by microscope and staining.Then the EPS was extracted by cold 95% ethanol.And it was separated and purified by dextran gel column chromatography.The effect of purified EPS on rheological properties was determined by rheometer.And the structure and composition of EPS were analyzed by IR and GC-MS respectively.The results are as follows:1.8 strains with good adhesion were screened out as HS4,HS8,HS10,LX4,LX5,LX6,AS8 and AS9,respectively.And 3 strains with higher EPS yield were screened out through Phenol-sulfuric acid method,as HS4,LX5 and AS8,respectively.And the EPS production of them were 123.79±3.02 mg/L,43.60±8.59 mg/L,67.82±1.94 mg/L,respectively.Through microscopic observation,the EPS produced by all strains of lactic acid bacteria were all cohesive exopolysaccharides.2.The crude extraction of EPS of HS4,LX5 and AS8 were 1108.23±18.33 mg/L,1636.05±54.67 mg/L and 1655.67±59.37 mg/L,respectively.After separated and purified by dextran gel column chromatography,the purified EPS was higher,more than 98%.3.The rheological test results showed that AS8-1-EPS and AS8-2-EPS could increase the apparent viscosity,stability of fermented milk and maintain the thermal stability of fermented milk.LX5-2-EPS could increase the storage stability of fermented milk.HS4-2-EPS can increase the stability of fermented milk and maintain the thermal stability of fermented milk.LX5-1-EPS could maintain the thermal stability of fermented milk.4.It was found that all EPS contained functional groups C-O-C and–OH,which proved that these two functional groups were the main components of EPS.Except HS4-2-EPS and AS8-2-EPS,all EPS had functional group-CH2-,and except HS4-1-EPS,all EPS had functional group C-C-O and –COOH.Only the EPS separated from strain HS4 had functional groups –COO.HS4-1-EPS and LX5-1-EPS had amidogent.LX5-2-EPS and AS8-2-EPS all had functional group C-C-C,and only LX5-2-EPS had amidogen.5.It was found that HS4-1-EPS and LX5-2-EPS were mainly composed of glucose which accounted for more than 80%,and also contained mannose and galactose.AS8-1-EPS was mainly composed of mannose which accounted for more than 59%,and included a spot of glucose,galactose,rhamnose,Arabia and xylose.HS4-2-EPS,LX5-1-EPS and AS8-2-EPS were mainly composed of glucose,mannose and some other components.It was indicated that the composition and structural characteristics of different EPS had an influence on the rheological properties of fermented milk.