Developing hydrophobic-hydrophilic protein structures by 3D food printing of sorghum and soy protein gels

Abstract

The goal of this study was to introduce the simultaneous use of hydrophobic-hydrophilic proteins bioinks for 3D food printing. Sorghum protein gel (SPG) at 25 % w/w and soy protein isolate gel (SPIG) at 11 % w/w were loaded into separate extruders. The effects of the first printed layer (SPG or SPIG), printing speed (10, 20 mm/s), and nozzle size (0.52, 0.64, 0.72 mm) on printability were evaluated. The textural properties, rheological characteristics, microstructure, crystallinities, and functional groups of the proteins were analyzed. Printing sorghum and soy proteins together helped balance essential amino acids, where lysine (94.7 %) and histidine (48.0 %) levels were improved in the 3D-printed sorghum protein formulation. The best printability and shape accuracy (>95 % match with the digital design) were achieved using SPG as the first layer, a 0.64 mm nozzle for SPG, a 0.52 mm nozzle for SPIG, and a printing speed of 10 mm/s. SEM images showed porous gel networks in the 3D-printed samples under optimized conditions. Chemical analysis indicated protein structure changes after gelation, and X-ray diffraction confirmed an amorphous structure in all samples. In conclusion, the findings emphasize the crucial role of process parameters in achieving the desired printability and structural integrity of SPG-SPIG. The novelty of this study lies in introducing a new bioink formulation with a balanced amino acid profile for food 3D printing, expanding the use of sorghum proteins.