Isolation,Purification And Structure Analysis Of Extracellular Polysaccharides From Lactic Acid Bacteria

Exopolysaccharides(EPS)can exist in two types:attached to the cell wall to form a capsule,and secreted into the medium to form mucus.These polysaccharides are indispensable conditions for improving the brightness and texture of products.Gelation is one of the important properties of whey protein(WP).It is used as thickener,microcapsule wall material,edible film and fat substitute.The gelation property of whey protein is affected by many factors.In this paper,the structure and rheological properties of exopolysaccharides isolated from Streptococcus thermophilus 6063 were analyzed.The results are as follows:1.The crude EPS was separated by cellulose gel chromatography and obtained two kinds of EPS.Two kinds of EPS were purified by the special polysaccharide gel purification system.One was neutral polysaccharide,named as ST 1-EPS,the other was acidic polysaccharide,named as ST2-EPS.2.Through the detection and analysis of gas chromatography-mass spectrometry,ST1-EPS was mainly composed of galactose,glucose and rhamnose,accounting for more than 80%,and also contained a little amount of mannose.ST2-EPS was mainly composed of galactose,mannose and glucose.The molecular weight of ST 1-EPS was 2.197×103kDa,and that of ST2-EPS was 1.419×102 kDa.3.Through the detection of infrared spectroscopy,the ST1-EPS and ST2-EPS all contained functional groups-OH,-CH2,-COOH,amide group,C-O-C and C-C-O.In addition,ST2-EPS contains glucuronic acid.4.Through the detection and analysis of nuclear magnetic resonance(NMR),ST1-EPS has five sugar residues,four of which are pyranose residues in the alpha configuration and one is a pyranose residue in the beta configuration.ST2-EPS has five sugar residues,three of which are pyranose residues in the alpha configuration and two are pyranose residues in the beta configuration.5.The results of rheological properties of EPS/WP system show that both EPSs can increase the apparent viscosity of EPS/WP system,and the rheological properties of two EPS/WP systems can be treated by different metal ions,pH and temperature.Both have a big impact but not the same.