Structure design in food 3D printing – Anisotropy formation and spatial distribution of fibrous structures using combined dual and coaxial extrusion for meat alternatives

The mechanical deformation behavior of anisotropic food matrices, such as meat and meat alternatives, is predominantly influenced by unidirectionally aligned fibrillar structures, but their specific contribution remains unclear because of their stochastic distribution, multilayered organization, and limited measurability. Therefore, this study aimed to develop and validate a novel 3D printing approach combining dual and coaxial extrusion. Using a pea protein isolate-wheat starch isotropic phase and an anisotropic pectin fiber phase, model systems with tunable fiber content and spatial distributions were produced. Mechanical deformation behavior was characterized through elastic double compression (10 % strain), plastic compression (80 % strain) and cutting tests. Fiber insertions resulted in matrices exhibiting anisotropic properties, showing fiber-dominated axial and matrix-dominated radial compression responses. Axially measured hardness and engineering Young's modulus were significantly influenced by fiber quantity and spatial distribution as a result of variable elastic and plastic fiber buckling behavior during axial compression. Cutting analyses revealed distinct force-displacement profiles depending on fiber localization, further allowing the extraction of fiber (0.07 N ± 0.02 N) and matrix average cutting force responses (0.014 N ± 0.002 N). This study highlights the potential of 3D printing to spatially resolve and control anisotropic deformation responses in food matrices, contributing to a better understanding of anisotropic deformation responses and to advance the design of next-generation complex food structures.