Network structure and gelation mechanism of kappa and iota carrageenan elucidated by multiple particle tracking

Abstract Network structure and gelation mechanism of kappa carrageenan (KC) and iota carrageenan (IC) were investigated using multiple particle tracking. Based on bulk rheology measurements, KC gels exhibit characteristics of a hard and brittle gel, whereas IC gels form a soft and so-called “weak-gel”. Particle tracking revealed the differences in the local physical properties of the two gel systems, which are not accessible with the macroscopic rheological measurements. The mean square displacement (MSD) of the probe particles were investigated to characterize changes in the gel network structure on cooling and storage. On cooling, the MSD of the probe particles in the KC solution decreased drastically at around the gelling temperature, demonstrating the trapping of particles within the network structures of KC gels. The MSD of the probe particles in the IC solution exhibited diffusive behavior even far below the gelling temperature on cooling, although the MSD decreased on storage. These results suggest that KC solutions formed a permanent gel network structure of KC chain aggregates that restricted the motion of particles on cooling. For IC at low temperatures, in contrast, the results suggested two possible structures: 1. clusters of IC chain aggregates, or, 2. a loose network with large pores, which allow the diffusion of particles and lead to weak-gel behavior. The aggregates further aggregate to form a more permanent gel network structure during storage.