Structure and mechanical properties of anisotropic agar gels obtained via unidirectional freezing

The food industry is presently placing significant efforts to replicate the anisotropic properties of food materials such as meats (e.g., plant-based whole-muscle meat alternatives). Approaches to generate anisotropic structures include extrusion, wet spinning, electrospinning, and shear cell technology. Another potential method to generate structural anisotropy is via unidirectional freezing. Here, we used unidirectional freezing to generate agar gels consisting of a honeycomb-like porous network of elongated and aligned pores. A custom-built Peltier system allowed for control of the freezing front velocity throughout the agar gels. A higher freezing velocity (10 µm/s) led to smaller pore sizes compared to the slower freezing velocity tested (2 µm/s). Texture analysis highlighted the significantly higher Young’s modulus in the gels when compressed in the axial vs. radial direction - a direct consequence of the unidirectional freezing. The proton spin-spin relaxation time revealed greater water mobility in the unidirectionally-frozen gel with larger pores. This study serves as the basis for the development of anisotropic hydrocolloid gels with a tunable microstructure and texture.