Viscosity studies on the polysaccharide gum from Rhizobium strain CB744

The apparent viscosity of aqueous solutions of polysaccharide gum from the nitrogen‐fixing bacteria Rhizobium strain CB744 has been determined to ascertain the gum's potential in commercial applications as a food conditioner. Solutions of the rhizobium gum had a viscosity that was dependent on the shear rate and showed thixotropic behaviour. The rhizobium gum solutions had an apparent viscosity of 0·05 Pa s at a concentration of 0·4% and 0·16 Pa s at a concentration of 1·0% when measured at 60 rev min −1 with a Brookfield Synchro‐Lectric viscometer at 15°C. The viscosity of the gum solution showed a moderate decrease with decreasing pH, while Sn 2+ and Ca 2+ did not have any effect. Interaction with other common food components was examined by adding sucrose, salt and polysaccharide food additives. Addition of sucrose (15%, w/v) reduced the viscosity by about 30%. Up to 2% NaCl had little effect but 3% NaClgave a considerable reduction in the viscosity of the gum. Addition of guar or xanthan gum did not produce a synergistic effect. Pasteurisation and slow freezing had a pronounced and irreversible effect on the viscosity of gum solutions.