3D layer-by-layer printing of protein-based soft solid foods: Challenges and potential for dysphagia foods

This study explores the application of additive manufacturing in developing foods suitable for individuals with mild to moderate swallowing difficulties (IDDSI levels 4-5). Functional extrusion-based 3D printing inks were designed and optimized for layer-by-layer fabrication using a 3D food printer. Two protein-rich ink formulations were developed: one containing commercial pea protein and the other based on sonicated lab-extracted sunflower proteins, obtained from micronized press cake upcycled from sunflower seed oil extraction. High- or low-acyl gellan gum, xanthan gum, sorbitol, and NaCl were incorporated to fine-tune viscoelasticity and flow behavior, ensuring precise control over the printed multilayer structures. Key techno-functional properties of the proteins, including emulsifying and water-holding capacities, were evaluated as critical parameters for printability. Inks rheology was characterized by using the Herschel-Bulkley model to describe flow behavior, while the Bohlin power-law model quantified viscoelastic properties from dynamic mechanical spectra. The pea protein-rich ink exhibited the highest yield stress, indicating greater structural integrity and printability. Both inks behaved as weak gels with soft-solid structures, but the pea protein ink displayed higher gel strength and a higher structural coordination index, correlating with increased elasticity and suitability for constructing robust printed structures. The extrusion process was carried out at 60 °C. Square grid structures (20×20×10 mm, 20% infill) were successfully printed to evaluate printability and structural stability. After post-printing stabilization, mechanical properties of the printed objects were assessed via uniaxial compression tests. The printed objects maintained their shape post-stabilization without collapsing. Compression tests confirmed the pea protein-based ink’s superior printability, as indicated by: i) sufficiently high elastic modulus to support its own weight and maintain layering; ii) high yield stress, enabling precise filament deposition while allowing for smooth extrusion; iii) greater structural cohesion, preventing deformation during printing; iv) pronounced strain softening, meaning the material gradually deforms, contributing to a chewier sensation before breakdown during oral processing. Overall, higher elasticity and structural cohesion in the pea protein ink resulted in greater printing precision and improved suitability for 3D-printed foods tailored to individuals with dysphagia.