Studies of the gel formation of κ-carrageenan above the coil-helix transition temperature range

Abstract

The temperatures of gel formation and coil-helix conformational transition of κ-carrageenan have been compared. For a 1·5% solution of the potassium salt of κ-carrageenan the gelation temperature is higher than the coil-helix transition temperature range when the KCl concentration exceeds 3−4 × 10 −2 mole litre −1. The gelation temperature, T g , and the midpoint temperature of the coil-helix conformational transition, T 1 2 c−h , are linearly increasing functions of the logarithm of the concentration of potassium ions, and δT g δ( lg[ K +]) > δ(T c−h 1 2 δ( lg[ K +]) Creep compliance studies on a 1·5% gel of κ-carrageenan in 0·11 m KCl have shown that the standard breakdown enthalpy of gel network crosslinks at temperatures above the coil-helix transition range is about 12 kJ mole −1. Upon helix formation this value increases 20 times. The relaxation behaviour of the κ-carrageenan gel in the high-temperature region is typical of thermoreversible gels. The network of such gels is generally made up of associates of macromolecules.