Separation, purification and characterisation of extracellular polysaccharides produced by slime-forming Lactococcus lactis ssp. cremoris strains

摘要

Five slime-forming Lactococcus lactis subsp. cremoris strains (ARH53, ARH74, ARH84, ARH87 and B30) isolated from Finnish cultured milk viili produced viscous exopolysaccharides (EPS) in skim milk cultures. The EPS were separated and purified by treatment with trichloroacetic acid, ethanol precipitation and dialysis. All EPS were anionic and composed of galactose, glucose and rhamnose of similar ratios. The 1H nuclear magnetic resonance spectrum of the EPS of strain ARH 74 showed high similarity with that of strain SBT 0495 EPS, previously reported to consist of pentasaccharide repeating units with a phosphodiester structural element. In dilute aqueous solutions (up to 0.1 g/dl EPS), the EPS showed polyelectrolyte effects, and they differed in viscosity. At a higher concentration of EPS (1%, w/v), the EPS solution showed a shear thinning behaviour, and the viscosity was temperature, pH and salt dependent. Addition of 1% EPS (w/v) to skim milk resulted in a significant increase in viscosity, and agel formed at 40deg C.