Gelling mechanism in kappa/iota-hybrid carrageenans : chemical structure and salt effects

Abstract

Kappa/iota-hybrid carrageenans (KI) are food additive which recently attracted an increased scientific and industrial interest as these are valuable sustainable alternative to kappa- and iota-carrageenans. Optimized KI (in terms of gel properties) have been isolated from Mastocarpus stellatus [1], Chondrus crispus and Anhfeltiopsis devenionsis seaweeds, thus providing a palette of chemical structures and inherent gel elasticity. Here we report a study on the gel mechanism of these KI in the presence of KCl or NaCl salts. KI hot solutions prepared at different polysaccharide concentrations and ionic strengths were stored at room temperature (230C) for 24h. Depending on the ionic strength and KI concentration, homogeneous solutions, stable and phase separated suspensions, or gels were formed, and a phase diagram for each KI can be determined. The rheological characterization of homogeneous phases (gels, suspensions and solutions) shows scaling law behavior with the KI concentration, and the salt effect on such scaling is discussed. Diluted gels, solutions and precipitated suspensions are further studied with atomic force microscopy to image the gel precursors. Structural results for all salt conditions and KI chemical composition will be compared to the scaling laws., and discussed in light of theories for hydrogel formation and elasticity. Moreover, a systematic comparison with gels and suspensions obtained by mixing kappa- and iota-carrageenan hot solutions is provided, and helps understanding the specificity of KI gels properties which are related to the unique statistical block copolymer chemical structure.