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 rhe-ological properties of obtained solutions and gels are reported. KI were extracted from Ahnfeltiopsisdevoniensis and Chondrus crispus seaweeds and showed different chemical composition, 48 mol% of kappacarrageenan (K) and 52 mol% of iota carrageenan (I), and 78 mol% of K and 22 mol% of I, respectively. Phasediagrams are systematically compared those of blends of commercial K and I (K + I) showing equivalentchemical compositions. Results confirm that KI clearly differ from mixtures of K and I. K + I form gels atlower polysaccharide concentration and ionic strength, and exhibit gel separation from a liquid phasewhen large amount (>0.1 mol/L) of KCl is used. In contrast, no syneresis was found in KI gels formed undersimilar conditions. Both KI and K + I gels are strain hardening, and show a concentration scaling of theelasticity with exponents ranging from 1.1 to 3.2 depending on the type of salt and ionic strength. Thestrain at break of KI gels does not show salt specificity and is similar to the strain at break of K + I gels inKCl under similar salt and polysaccharide concentrations. K + I gels in NaCl are more fragile than in KCl,thus showing salt specificity.