Phase diagrams of hybrid carrageenans extracted from Ahnfeltiopsis devoniensis and Chondrus crispus

Abstract

NaCl and KCl phase diagrams of two kappa/iota-hybrid carrageenans (KI) are established, and the rheological properties of obtained solutions and gels are reported. KI were extracted from Ahnfeltiopsis devoniensis and Chondrus crispus seaweeds and showed different chemical composition, 48mol% of kappa carrageenan (K) and 52mol% of iota carrageenan (I), and 78mol% of K and 22mol% of I, respectively. Phase diagrams are systematically compared those of blends of commercial K and I (K+I) showing equivalent chemical compositions. Results confirm that KI clearly differ from mixtures of K and I. K+I form gels at lower polysaccharide concentration and ionic strength, and exhibit gel separation from a liquid phase when large amount (>0.1mol/L) of KCl is used. In contrast, no syneresis was found in KI gels formed under similar conditions. Both KI and K+I gels are strain hardening, and show a concentration scaling of the elasticity with exponents ranging from 1.1 to 3.2 depending on the type of salt and ionic strength. The strain at break of KI gels does not show salt specificity and is similar to the strain at break of K+I gels in KCl under similar salt and polysaccharide concentrations. K+I gels in NaCl are more fragile than in KCl, thus showing salt specificity.