Relation between deformation and relaxation of hydrocolloids-starch based bio-inks and 3D printing accuracy

For a starch-based food (enriched by proteins and functionalized by hydrocolloids) for 3D food printing and its quality control, knowledge of the rheological behavior of the inks during and after the printing process and its influence on the printing accuracy is urgently needed. Mechanical forces, which occur during the 3D printing process, are strongly influencing the pseudoplastic networks of the food inks. To investigate the influence of the deformation and recovery behavior of these networks and its effect on printing accuracy, five different hydrocolloids (xanthan, methylcellulose, hydroxypropyl methylcellulose, alginate, and starch) were used to stabilize cereal-based food inks. The deformation and relaxation behavior of these materials was investigated using the three-intervall thixotropy test (3ITT), which allows to imitate the mechanical conditions occurring during the 3D printing process. Depending on the stabilization mechanism of each hydrocolloid, the structure recovery varies between 48.03% (HPMC) and 78.56% (starch), based on the storage modulus (G') value after the structure deformation due to extrusion. This is consistent with the results of printing trials (assessed by imaging techniques) leading to a positive linear correlation (R² > 0.89) between the strength of the network and printing stability. The deformation of the inner structure results in a weaker object stability. For future design of edible food prints, a process control of the time between the deposition of layers has to be considered.