Identifying relationships between the chemical structure and the rheological properties of Kappa/Iota-Hybrid Carrageenans

Abstract

Kappaiiota-hybrid carrageenans (Kl) are gelling natural polysaccharides extracted from seaweeds belonging to the Gigartinaceae family. The increasing demand for such natural gelling agents in a wide range of industrial applications calls for a sustainable production of Kl and a better understanding of the interplay between the chemical structure and the rheological properties of the gels obtained by cooling hot Kl solutions in the presence of salts [1]. Following preliminary studies on the gel properties of Kl extracted from wild seaweed [2-4], Masitocarpus stetiaius, Ahnfeitiopsils devoniensis and Chondrus crispus seaweeds were collected on the Portuguese coast and then used as water cleaning agents in a fish THITI1, in order to produce an Integrated Multi-Trophic Aquaculture (IMTA) system [5] allowing the sustainable production of carrageenophytes. Alter a month in IMTA, seaweeds were alkali treated with NaOH or KOH and Kl with different gelling properties in NaCI and KCI were extracted. Here we report on the gel properties measured with small amplitude oscillatory shear, on the gel fracture behaviour and on the shear and extensional visooelastic properties of solutions obtained for Kl concentrations below the gel formation. The rheological parameters are systematically compared with the chemistry of the Kl assessed with DRIFT and NMR. As a result, the general conclusions documented in previous studies [1-5] will be revisited.