Chemical structure and gel properties of carrageenans from algae belonging to the Gigartinaceae and Tichocarpaceae, collected from the Russian Pacific coast

Abstract

The chemical and gel characteristics of carrageenans isolated from the most abundant algal species growing on the Russian Pacific coast – Chondrus pinnulatus, C. armatus and Iridaea cornucopiae belonging to the Gigartinaceae and Tichocarpus crinitus from the Tichocarpaceae were investigated. The polysaccharides were identified by FTIR and NMR spectroscopy as predominantly κ-carrageenans with traces of ι-type (Gigartinaceae) and κ / β-type repeating structures (Tichocarpaceae) together with a small quantity of λ-carrageenan (10%). The chemical structure and the hydrodynamic properties play a determinant role on the rheology of these carrageenans. κ-Carrageenans from the Gigartinaceae displayed good gelling properties. The highest gel strength was obtained from C. pinnulatus (1232.7 Pa) at a 2.5% polymer concentration, while carrageenans from the Tichocarpaceae formed very weak gels (77.4 Pa) at the same concentration. Optimum gel characteristics were found with 1.0–2.0% KCI concentrations for kappa- carrageenans from Gigartinaceae and 0.75% for T. crinitus. The flow curves of λ-carrageenans solutions from the Gigartinaceae were similar, all between 20 and 65 °C, and characteristic of conformational disordered ‘random coil’ polysaccharides. Carrageenans from T. crinitus displayed the properties of ’random coil' only at high temperatures.