Ultrasound effect used as external stimulus for viscosity change of aqueous carrageenans

Ultrasound (US) serves as a stimulus to change shear viscosity of aqueous polysaccharides of ι-carrageenan, κ-carrageenan and, agar. The US effect was compared in their aqueous solutions at 60 °C for the US frequency of 23, 45, and 83 kHz. Under the US condition with 50 W at 45 kHz, the shear viscosity of each aqueous solution was decreased significantly. Subsequently, when the US was stopped, the shear viscosity returned back to the original value. In addition, the US showed different effects of the US frequency over the viscosity change in the three kinds of polysaccharides. When the US frequency was changed, the US effects were less at 83 kHz and 28 kHz for the shear viscosity change. In addition, as NaCl was present in the aqueous solution, the viscosity change decreased by the US exposure. These results suggest that the US effect on the viscosity reduction was influenced by the condition of polymer coil conformation, which was expanded or shrank by electrostatic repulsion of the SO3− groups. FT-IR analysis supported that the hydrogen bonds of carrageenans were broken during the US exposure. Using Fourier self-deconvolution for the FT-IR spectra without and with US exposure suggests that the US influenced the hydrogen bonds of water and the OH group of polysaccharides.

► Ultrasound could change shear viscosity of aqueous carrageenans and agar solutions.
► At higher SO3− groups, US effect was suppressed by the extended polymer chains.
► FT-IR deconvolution proved that the free OH group increased after the US exposure.
► Hydrogen bonds of the polysaccharides were broken by US effect.