Lester C. Geonzon, Xinye Zhuang, Amos M. Santoya, Rommel G. Bacabac, Jingli Xie, Shingo Matsukawa
Dynamic rheology and particle tracking experiments were carried out to investigate the gelation mechanism and network structure of mixed κ-carrageenan (KC) and λ-carrageenan (LC) gels on the macroscopic and microscopic levels. Mixtures of KC and LC (total carrageenan concentration = 1.5%, K+ concentration = 15 mM) were prepared at different mixing ratios. The storage modulus (G′) was highest for pure KC and decreased monotonously with decreasing KC content. The mean square displacement (MSD) of probe particles was used to characterize the network on cooling and after one day of storage. On cooling, a single step decrease in the ensemble-averaged MSD was observed, in agreement with the rheological measurements. Time-averaged MSD values of individual particles showed a large distribution after one day in storage, especially for gels with low content of KC. This heterogeneity reflects microstructural heterogeneity, suggesting phase separation into KC-rich and LC-rich domains. Individual particle MSD values showed a bimodal distribution. The MSD could be described as a power-law, MSD~τα, with τ the lag time. The exponent α also showed a bimodal distribution. These findings suggest that two groups of probe particles with distinctly different mobilities are present in the mixed gels with particles of higher and lower mobilities present in the LC-rich and KC-rich phases. Based on the rheological results, as well as the particle tracking experiments, we propose that mixtures of KC and LC separate into a continuous phase and a non-continuous filler phase, with the continuous phase being made up of the more concentrated carrageenan. When the concentrations of the two carrageenans are roughly equal, we suggest that a bicontinuous phase-separated network is formed. © 2020
Department of Food Science and Technology, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo, 108-8477, Japan; Department of Food Science and Technology, East China University of Science and Technology, No.130, Meilong Road, Xuhui District, Shanghai, 200237, China; Medical Biophysics Group, Department of Physics, University of San Carlos, Cebu City, 6000, Philippines
