Elaborating Spatiotemporal Hierarchical Structure of Carrageenan Gels and Their Mixtures during Sol–Gel Transition

The control of the rheological properties of carrageenan gels from hierarchical structure design is very important for food and biotechnological applications. In this study, the viscoelastic properties from linear to nonlinear regimes and temperature-dependent spatiotemporal hierarchical structure of κ-(KC), ι-(IC) carrageenan gels, and their mixtures (KCIC) were investigated using dynamic rheology, small-angle neutron scattering (SANS), dynamic light scattering (DLS), and pulsed nuclear magnetic resonance (NMR). The nonlinear viscoelastic measurement revealed the characteristic signature of the KC and IC gels under large-amplitude oscillatory shear (LAOS), where IC showed a characteristic strain-stiffening and broke at large strain amplitude, while KC did not show a strain-stiffening and broke at small strain amplitude. The difference in the LAOS response was corroborated by the difference in the spatial and temporal hierarchical structures of the gels. The characteristic cross-sectional size of the aggregates, R g, of carrageenan gels measured by SANS confirmed that KC formed large bundles of rigid aggregates due to the extensive aggregation of KC during gelation. Furthermore, the temporal dynamics of the aggregates were resolved by pulsed NMR, demonstrating that IC gels formed loose aggregates in contrast to highly packed KC aggregates. Meanwhile, DLS revealed that KC formed a completely frozen network structure. Therefore, based on the collective understanding of carrageenan gels’ spatiotemporal hierarchical network structure, we demonstrate that the LAOS response of the carrageenan gels corresponds to the size of the aggregates and the dynamics of the network.