Insight into the glucose cosolvent induced gelation of κ-carrageenan by broadband dielectric spectroscopy

To gain insight into the mechanism of glucose cosolvent induced gelation of kappa-carrageenan, the sol to gel transition of kappa-carrageenan with 0-40 wt% glucose and the water molecular dynamics of these kappa-carrageenan/glucose gels are studied by broadband dielectric spectroscopy. A dielectric relaxation caused by counterion fluctuation was observed in the radio frequency range. Its dielectric increment and relaxation time change with temperature and glucose concentrations, and meaning the glucose concentration does not affect the chain conformation of kappa-carrageenan in sol state, but affects its chain conformation in gel state. During cooling, the conductivity decreases and an inflection point appears which shifts to higher temperature with glucose concentration. This proves the glucose induced gelation of kappa-carrageenan changed. An obvious relaxation from the contributions of free water and bound water also be observed in the microwave frequency range. Its dielectric increment and relaxation time change with glucose concentrations. Based on dielectric increment, the molar concentration of bound water molecules is obtained by the aid of Cavell equation. The change of molar concentration of bound water molecules with glucose concentration supports the hypothesis about glucose cosolvent binding to kappa-carrageenan gel. (C) 2020 Elsevier B.V. All rights reserved.