Molecular recognition during sol–gel and gel–sol transition of kappa–iota carrageenan mixtures

Abstract

Sol–gel and gel–sol phase transitions of kappa–iota (κ–ι) carrageenan mixtures in two types of salts were studied using photon transmission technique. Here, KCl and CaCl2 were chosen as the proper salts for the carrageenan mixtures. Coil-to-double helix (c-h) and double helix-to-dimer (h-d) phase transitions of carrageenan mixtures in monovalent and bivalent cation solutions were studied upon heating and cooling by using photon transmission technique. Photon transmission intensity, I tr was monitored against temperature to determine the (c-h) and (h-d) transition temperatures (T ch and T nd). Two distinct transition regions were observed in both heating and cooling of the carrageenan-bivalent CaCl2 salt system. At the first step of heating process dimers decompose into double helices by making (d-h) transition. At the high temperature region (h-c) transition takes place. Carrageenan-monovalent KCl salt system presented only (c-h) and (h-c) transitions upon cooling and heating processes. Transition temperatures at the heating and cooling processes were obtained. A hysteresis was observed between (h-c)–(c-h) and (d-h)–(h-d) transitions for the monovalent and bivalent cations respectively.