Structure-Function Relationship of a Gellan Family of Polysaccharide, S-198 Gum, Produced by Alcaligenes ATCC31853

The structure-function relationship of a gellan family of polysaccharides, S-198 gum produced by Alcaligenes ATCC31853 was investigated in terms of rheological aspects. The flow curves of S-198 gum showed plastic behavior above 0.3%. Gelation did not occur in S-198 gum solution at low temperature (0 ̊C), even at 0.8%. Both the viscosity and the elastic modulus remained constant with increasing temperature up to 80 ̊C. The elastic modulus decreased a little with the addition of CaCl2 (6.8 mM), but then once again remained constant up to 80 ̊C. The highest elastic modulus was observed for deacylated gellan gum with the addition of CaCl2 and increased slightly with increasing temperature up to 80 ̊C, which was considered to be a transition temperature, after which it decreased rapidly. The elastic modulus of S-198 gum in the presence of urea (4.0 M) was lower than that in aqueous solution at low temperature (0 ̊C), but remained constant with increasing temperature up to 80 ̊C. The intramolecular associations, (hydrogen bonding and van der Waals forces of attraction), of S-198 gum molecules in aqueous solutions were proposed. The gellan family of polysaccharides, S-198, S-88, S-657, rhamsan, welan and gellan gum, provided a good opportunity to investigate the structure-function relationship for polysaccharides.