Rheological study of α- and κ-carrageenan expansion in solution as effects of the position of the sulfate group

Abstract

The viscosity of carrageenan solutions in the coil state was greater for α-carrageenan (α-Car) compared with that for κ-carrageenan (κ-Car); thus, the impact of one sulfate group on 3,6-anhydro-D-galactose was compared with the impact of one sulfate group on D-galactose units of the carrabiose residues. The thermal expansion coefficient of the solutions, B2 × Tc, characterizes the way the viscosity decreases because of extension of the physical bonds of the systems to their rupture point (Tc) under increasing temperature. The Tc and B2 × Tc of water were equal to (100 ± 5) °C and (1.57 ± 0.05) × 10−2/°C, respectively. The Tc of the α-Car and κ-Car systems increased after the addition of CaCl2 and KCl, respectively, and with increasing polysaccharide concentration. However, the B2 × Tc of the α-Car and κ-Car systems were rather sensitive to CaCl2 and KCl, respectively. In the overall solutions examined, the expansion of α-Car systems was found to be between 1.5 × 10−2/°C and 1.61 × 10−2/°C, greater than the expansion of κ-Car systems, which was between 1.5 × 10−2/°C and 1.2 × 10−2/°C. Thus, α-Car is a good alternative to κ-Car for reducing syneresis phenomena, and its sensitivity as ι-Car to divalent cations would be due to the anhydro cycle.