Ultrasound Viscoelastic Properties of Biomass Polysaccharide Hydrogels as Evaluated by Rheometer Equipped with Sono-Device

A viscoelastic rheometer was equipped with a sono-device and a water bath to enable measurement of storage moduli G′ and loss moduli G″ of biomass polysaccharide hydrogels such as Kanten agarose, κ-carrageenan, and konjac glucomannan under ultrasound (US) exposure. The action of low power of 43 kHz US on their hydrogels significantly decreased G′ of Kanten agarose and carrageenan after a few seconds of US exposure 0.1% strain. When US with 20 W output power was exposed under mechanical strain at 0.1%, lower values were obtained cyclically for 3 min US intervals. The values then reverted to the original moduli values when US was stopped in cases of Kanten agarose and carrageenan hydrogels. As G″ values were increased during US operation, the anhydro-L-galactose segments in their hydrogels were unable to relax the external US forces within the gel sufficiently, thereby leading to gel structure collapse at a higher strain percentage. These results suggest that US exposure induced deformational change in the hydrogel structure formed by hydrogen-bonded cross-links. However, US deformation was less in the case of deacetylated cross-linkage in konjac glucomannan hydrogel.