Comparison of cation effects on phase transitions of kappa and iota carrageenan

Abstract

Abstract Phase transitions of kappa and iota carrageenan in KCl, NaCl, and CaCl, solutions were separately studied during heating and cooling processes by using fluorescence technique. Scattered light, I sc and fluorescence intensity, I was monitored against temperature to determine the critical transition temperatures and exponents. Kappa and iota carrageenans with monovalent (KCl, NaCl) salt system presented only coil to double helix (c-h) and double helix to coil (h-c) transitions upon cooling and heating processes, respectively. Two transition regions were observed in both heating and cooling of the iota carrageenan in CaCl 2 solution while in kappa carrageenan only (c-h) and (h-c) transitions was detected. During heating, dimers decompose into double helices by making (d-h) transition. At the high temperature region (h-c) transition takes place. During cooling, back transitions repeat themselves. A hysteresis was observed between (h-c) and (c-h) for the kappa and iota carrageenan salt system (except CaCl 2 ), respectively. Dimer to double helix (d-h) and double helix to dimer (h-d) transitions were observed for iota carrageenan in CaCl 2 salt. The gel fraction exponent b was measured and found to be in accord with the classical Flory-Stockmayer Model for both kappa and iota carrageenan salt systems