Aggregation and disaggregation of Aeromonas gum in an aqueous solution under different conditions

Abstract

The aggregation and disaggregation ofAeromonas (A) gum, an acidic heteropolysaccharide, were investigated by viscometry, a fluorescent probe, and gel permeation chromatography combined with laser light scattering techniques in aqueous solutions containing desired NaCl at different temperatures. The A gum had a strong tendency of aggregation and high viscosity in the aqueous solutions. The weight-average molecular weight, z-average radius of gyration, weight-average molar number (w ag ), and apparent aggregation number (N ap ) of the aggregates were investigated and discussed. The results indicated that there were three regions that corresponded to three kinds of aggregates and two transition temperatures at about 35 and 75 °C in the disaggregation course. When the temperature was higher than 75 °C, the w ag hardly changed, and there was still a certain amount of aggregates even at 100 °C, indicating that the aggregates were difficult to disrupt completely. Moreover, the aggregation was thermally irreversible. Decreasing polysaccharide concentration reduced the content of the aggregate. However, N ap remained constant around 20, independent of the polysaccharide concentration in a 0.5 M NaCl aqueous solution at 25 °C. At a salt concentration greater than or equal to 0.05 M, the aggregation was almost independent of the salt concentration used here.