Structure characterization and cryoprotective activity of an exopolysaccharide from Pseudoalteromonas sp. LP6-12-2

Non-toxic natural antifreeze agents are urgently needed in many fields. Exopolysaccharides produced by psychrophilic bacteria from harsh habitats, such as Antarctica, to battle cold environments are a significant source of biological antifreeze agents. In this study, a homogeneous exopolysaccharide (EPS0-1) was extracted from Antarctica Pseudoalteromonas sp. LP6-12-2. Using High-performance gel permeation chromatography and High-efficiency anion chromatogram, respectively, the homogeneity, molecular weight, and monosaccharide composition of EPS0-1 were examined. EPS0-1 with a molecular weight (Mw) of 4351.31 kDa was an α-configuration polysaccharide containing uronic acid, amino and sulfuric acid groups, and composed of galactosamine hydrochloride, rhamnose, glucosamine hydrochloride, galactose, glucose, mannose, galacturonic acid, and glucuronic acid with rates of 1.40:9.40:4.90:32.0:37.2:6.50:4.10:4.40, respectively. Congo red test and I2-KI reaction found that the triple helix structure of EPS0-1 polysaccharide chain was weakly bound internally, with a longer side chain and/or more branches. The smooth and dense surface of EPS0-1 under Atomic force microscopy and Scanning electron microscopy revealed that it was large polysaccharide particles. Freeze-thaw cycle and freezing point determination experiment showed that EPS0-1 may significantly increase E. Coli's freezing resistance and decrease the solution's freezing point, respectively. EPS0-1 was capable of increasing the viscosity of the solution and displaying a high degree of thermal stability, which was proved by the rheological properties. And it was not hazardous to human normal liver cell line (LO2) in a specific concentration range. Therefore, the findings of this investigation established the basis for EPS0-1 as a potential antifreeze and food functional component.