Development and characterization of protein-rich mixed-protein soft foods for the elderly with swallowing difficulties.

Protein-rich custards were developed for elderly individuals with dysphagia by combining soy protein isolate (SPI) and milk protein concentrate (MPC), with and without transglutaminase (TG). The formulations were designed to resemble the texture, rheology, and swallowability of MPC-only custard. Custards with 1:1 and 1:2 SPI-to-MPC ratios, both with and without 0.2 % TG, were evaluated against MPC-only and SPI-only custards as benchmarks. Without TG, mixed-protein custards exhibited lower viscosity, hardness, gumminess, chewiness, and stability due to molecular incompatibility disrupting the protein networks. TG addition significantly enhanced gel strength and water-holding capacity in mixed formulations. The SPI-MPC (1:2) custard with 0.2 % TG showed optimal performance and met Level 6 IDDSI standards. Atomic force microscopy (AFM) revealed that nanoscale protein-protein interactions were critical in stabilizing the gel network. These findings support the development of high-protein, custard-style soft foods using blended dairy and plant proteins to improve nutrition and swallowing safety for the elderly.