Evaluation of rheology and printability of 3D printing nutritious food with complex formulations

Understanding rheological properties and printability of complex food formulations is crucial for 3D printing. While nutritious formulations have been reported in the literature, these are still scarce when compared to the non-nutritious ones. These so-labeled nutritious formulations are achieved with few ingredients, leading to less challenging printability issues. The nutritious formulations presented here are reported for the first time and include up to 9 ingredients, including by-products (orange peel) and sustainable proteins (insect flour). This work aimed to evaluate and to correlate the printability and the rheological properties of nutritious complex food formulations. The concentration of pregelatinized corn starch (4–10% (w/w)) and printing temperature (27–47 °C) were varied. Rheological characterization of the studied food inks (i.e., amplitude sweep, shear-viscosity test, shear-recovery test, time-dependent shear test, temperature ramps, temperature sweep in the oscillatory mode) was performed. Printability was evaluated via a digital image analysis of the geometric features of the printed structures. An increment in the concentration of pregelatinized starch (from 4% to 10%) raised the yield stress and the storage modulus from 87.5 to 883.2 Pa and from 1004.9 to 2620.9 Pa, respectively. However, high values of rheological parameters did not correspond to an improved printability. For instance, the printability evaluation showed that formulations with 6% and 8% of pregelatinized starch were more suitable for printing than the one with 10%. Finally, initial mathematical correlations between rheology and printability were obtained and could be of benefit to potentialize complex food printing systems. The results presented showed that both, rheology, and printability analyzes, must be performed when printing complex formulations towards the development of personalized food items. More research in this regard is needed to develop new methodologies for the evaluation of 3D printing materials.