Lester C. Geonzon, Faith Bernadette A. Descallar, Lei Du, Rommel G. Bacabac, Shingo Matsukawa
Studies on the gelation mechanism and network structures of κ-(KC) and ι-(IC) carrageenan gels and their mixtures at different length scales from macroscopic to microscopic and molecular levels are reviewed. Studies on pure carrageenan gels revealed the gelation mechanism to induce different gelation abilities. Particle tracking methods characterized the local network structure of weak carrageenan gels. Nuclear magnetic resonance (NMR) studies revealed the aggregation behavior of carrageenans, suggesting a preferential aggregation for longer carrageenan chains in the network. This review also addressed whether the mixtures of KC and IC formed a phase-separated or interpenetrating network structure. Macroscopic measurements accompanied by a theoretical model suggested the formation of a phase-separated network structure. Studies on the self-diffusion of carrageenan chains and the diffusion of probe polymer by NMR, however, proposed two possible structures, interpenetrated network or phase-separated network with a domain size of less than 450 nm. Fluorescence-labeled carrageenan viewed by using confocal laser scanning microscopy showed a homogenous network of KC in the mixtures of KC/IC compared to pure KC suggesting possible co-aggregation or interpenetrated network of KC and IC chains. Conversely, microscopic characterization using particle tracking revealed a bimodal distribution in diffusivity with local and diffusion mode characteristics. This result implied the formation of a phase-separated network structure comprised of KC-rich and IC-rich domains. Nevertheless, despite the progress made to understand the interactions of carrageenans in the mixtures, further studies are required to clarify the gelation mechanism and network structures in the mixed carrageenan gels. © 2020 Elsevier Ltd
Department of Food Science and Technology, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo, 108-8477, Japan; School of Biotechnology, Department of Food Science and Engineering, East China University of Science and Technology, Meilong Road 130, Shanghai, China; Medical Biophysics Group, Department of Physics, University of San Carlos, Cebu City, 6000, Philippines
