Gel Strength of Kappa‐Carrageenan as Affected by Cations

SUMMARY– Kappa carrageenan was ion‐exchanged with Al +3 , NH 4 , +2 , Ca +2 , Fe +3 , Fe +3 , Mg +2 , Na +2 and Sn +2 . The gelling temperature and gel strength were determined for 1% exchanged kappa carrageenan gels prepared with 0.0375,0.075 and 0.15 N solutions of each of the exchanging cations; 1% exchanged kappa carrageenans with 0.0375, 0.075 and 0.15 N KCI, and non‐exchanged kappa carrageenan with the same concentrations of AlCl 3 , NH 4 Cl, CaCl 2 , FeCl 2 , FeCl 3 MgCl 2 KCl, NaCl and SnCl 2 . Ion‐exchange with Al, Fe +2 , Fe +3 and Sn prevented gel formation. The other ion‐exchanged carrageenans had signicantly lower gel strength than the non‐exchanged carrageenan in a corresponding cation solution. Furthermore, the Mg‐ and Ca‐exchanged carrageenans had greater gel strengths than the NH 4 and Na‐carrageenans. Use of KCI with the NH,‐, Ca‐, Mg‐ and Na‐exchanged carrageenan resulted in increased gel strength, but the Al, Fe +2 , Fe +3 and Sn‐exchanged carrageenans still did not form a gel. The rank order of the gel strength of the NH 4 , Ca‐, Mg‐ and Na‐exchanged carrageenan dispersed in KCI was similar for the exchanged carrageenan in solutions of the exchanging cation, but the gelling temperatures and gel strength of the former approached that of the non‐exchanged carrageenan in similar concentrations of KCl. For the non‐exchanged carrageenan at the 0.075 N level of salt concentration, the effect of cation was K > Ca, Mg > Fe +2 , NH 4 < Na, Sn < Fe +3 , Al (P < 0.001). Use of increasing concentrations of NH,Cl, NaCl, KCl and SnCl 2 resulted in increased gel strength, whereas increasing concentrations of CaCl 2 , FeCl 3 and MgCl 2 decreased gel strength. These differences were reflected in a slightly different rank order for the 0.15 N level of salt.