Using power ultrasound for cold gelation of kappa-carrageenan in presence of sodium ions

Usually a heating stage is required to solubilize kappa carrageenan dispersions for gel formation on cooling. This work reports cold gelation of kappa carrageenan in the presence of sodium ions using power ultrasound without using any heating stage. Carrageenan gels were prepared using ultrasound in the presence or absence of NaCl and their textural properties were compared with the gels prepared with conventional heating method. Mechanical properties of the gels strongly increased with ultrasonication time up to a certain level, and further sonication reduced mechanical characteristics. Addition of Na+ ions after ultrasonication was more effective in increasing textural hardness than when Na+ is present during ultrasonication. Microscopic images demonstrated that increasing ultrasonication time up to a certain level leads to coherent gel networks and further ultrasound has a negative impact on the gel network. Solubility and intrinsic viscosity results are also presented. Moreover, Maxwell model with three elements was used to analyze stress relaxation data.