Multifunctional Effects of Peach Palm (Bactris gasipaes) Heart Powder on the Printability, Structural Properties, Probiotic Viability, and Gastrointestinal Digestion of Soy Protein-Based 3D-Printed Foods

Peach palm (Bactris gasipaes) heart is a sustainable, fiber- and polysaccharide-rich ingredient with potential for plant-based food structuring. This study investigated peach palm heart powder (PPHP) as a functional co-ingredient in soy protein isolate (SPI)-based inks for extrusion-based 3D food printing, focusing on rheology, printability, microstructure, molecular interactions, texture, and in vitro digestibility. Increasing PPHP concentration enhanced apparent and complex viscosity, storage modulus (G′), deformation resistance, and structural recovery while maintaining strong shear-thinning behavior, improving printing performance; PPHP8 showed the lowest dimensional deviation (0.25%) and highest shape fidelity (100.25%). PPHP was progressively incorporated into the SPI matrix, forming a denser protein–polysaccharide network primarily through non-covalent interactions, as indicated by microstructural and SDS–PAGE analyses. PPHP reduced hardness, gumminess, chewiness, and resilience but maintained springiness, enabling texture modulation, and FTIR/PCA revealed a shift from α-helical toward β-sheet-rich protein conformations, consistent with enhanced hydrogen bonding. Protein hydrolysis during simulated digestion and B. longum subsp. longum viability were not significantly compromised by PPHP incorporation. These findings demonstrate that PPHP can be strategically incorporated to tailor the rheological and textural properties of SPI-based inks for 3D printing without compromising nutritional functionality, supporting its potential as a sustainable structuring ingredient for next-generation plant-based printed foods.