Gelation behaviour of aqueous solutions of different types of carrageenan investigated by low-intensity-ultrasound measurements and comparison to rheological measurements

The gelation of different carrageenans in aqueous solutions was investigated by ultrasound at 7.8 MHz and by oscillating rheological measurements. The gelation of κ-, κ/ι-hybrid-carrageenan as well as a mixture of κ- and ι-carrageenans causes an increase in ultrasonic attenuation and a decrease in ultrasonic velocity. However, the gelation of ι-carrageenan, which could be detected by the oscillating rheological measurement, did not cause detectable changes in the ultrasonic measurement. Different gelation behaviours of a κ/ι-hybrid- carrageenan and a mixture of κ- and ι-carrageenans were observed by both techniques. This illustrates that the analytical techniques studied, which are based on different principles, can differentiate the gelation behaviour of different carrageenan systems. This might have important implications on the elucidation of gel formation mechanisms which, for complex systems, cannot be explained using only one single analytical technique.