Scaling Behavior of Physical Properties of Food Polysaccharide Solutions: Dielectric Properties and Viscosity of Sodium Alginate Aqueous Solutions

The dielectric properties of a typical ionic food polysaccharide, alginates with different chemical compositions and molecular sizes, were investigated with special relevance to the solution viscosity. The dielectric relaxation around 1 MHz due to the fluctuation of bound counterions was analyzed. The polymer concentration, C, dependence of the dielectric increment, Δε, and that of the relaxation time, τ, are summarized as Δε ∝ C 1/3 and τ ∝ C - 2/3 at the dilute region and as Δε ∝ C 0 and τ ∝ C - 1 at the semidilute region for all of the samples, in good agreement with the scaling relations predicted by polyelectrolyte solution theories. The crossover concentration, C *, from the dilute to the semidilute region was determined as the concentration at the intersection of the two regions. The concentration dependence of the relative viscosity, η rel, was also expressed by two scaling equations: (η rel − 1) ∝ C 1 at low concentration and η rel ∝ C 1/2 at high concentration. The crossover concentration, C *, determined by the viscosity agreed with that determined by the dielectric measurement. These results suggest that the behavior of the physical properties of the food polysaccharide solutions would be understandable on the basis of the scaling concept, the dielectric relaxation measurement being an effective method for analyzing the polyelectrolyte solution structure contributing to the physical properties of the systems.