Rheological properties of gellan, κ-carrageenan and alginate polysaccharides: effect of potassium and calcium ions on macrostructure assemblages

The effect of added ions (0.5 mM K+ or 0.25 mM Ca2+) on the critical overlap (C*) and gelation (Co′) concentrations for gellan, κ-carrageenan and alginate polysaccharides were investigated using steady shear rheometry. Both C* and Co′ decreased for all solutions with added salts, a trend more pronounced for gellan and alginate with added Ca2+, and κ-carrageenan with added K+. Aggregation near the sol–gel transition was modeled as a percolation-type transition. In addition, the frequency dependence of the viscoelastic storage (G′) and loss (G″) moduli for bulk and localized areas within a 0.7% (w/w) gellan sol were measured using a controlled stress and oscillating magnetic bead rheometer, respectively. Flow behavior of the bulk was in the terminal and plateau relaxation regions of the viscoelastic spectrum, whereas localized behavior was in the plateau and rubber–glass transition regions.