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Rheology and microstructure of κ-carrageenan under different conformations induced by several concentrations of potassium ion

Núñez-Santiago, M.C., Tecante, Alberto, Garnier, Catherine, Doublier, Jean Louis
Food hydrocolloids 2011 v.25 no.1 pp. 32-41
gels, ions, microstructure, polymers, potassium, potassium chloride, rheology, salt concentration, viscoelasticity, viscosity
Rheology, micro-DSC and confocal microscopy were used to study the effect of potassium ion on the viscoelastic behavior, disorder–order transition and microstructure, respectively, of κ-carrageenan in solution under different conformations at 60, 25 and 9°C. At 60 and 25°C the rheological behavior of 0.5% κ-carrageenan with 0–80mmol/dm³ and 0–5mmol/dm³ KCl, respectively, was typical of viscoelastic solutions of random coiled polymers. At 9°C and below a critical ionic concentration of about 7.0mmol/dm³, κ-carrageenan adopted an ordered conformation in which helical structures did not aggregate and hence did not form self-supporting gels. Changes in polysaccharide stiffness were estimated from intrinsic viscosity variations as a function of ionic content. In the ordered state, the stiffness was higher than in the disordered state, whereas a liquid-like viscoelastic behavior was still exhibited. In 0.5% κ-carrageenan at 25°C, increasing KCl from 0 to 300mmol/dm³ produced gels of increasing rigidity. However, above 100mmol/dm³ such increase was marginal. Confocal images evidenced a three-dimensional network whose continuity depends on polysaccharide and salt concentrations. These observations are consistent with the rheological behavior of the self-supporting gels obtained with κ-carrageenan concentrations in the range of 0.05–1%.