Pressure-induced structural and rheological changes in homogenized agar and agar-collagen fluid gels for dysphagia diets

This study investigated the potential of high-pressure homogenization as a post-production modification to reduce particle size and enhance swallow-related properties of agar-based fluid gels. The effects of pressures ranging from 10 to 60 MPa on the stability, structural changes, and swallow-related rheological characteristics of dysphagia-oriented pre-prepared agar (1.5%) and agar-collagen (20%) fluid gels were examined. High-pressure homogenization reduced agar particle size, enhancing interactions among new agar domains. Droplet size and microstructural analyses showed that higher pressures produced smaller particles, which then re-aggregated after reaching a critical concentration. However, adding collagen prevented this re-aggregation, with particle size decreasing from 182.76 to 65.82 µm as pressure increased from 0 to 60 MPa. All treated fluid gels exhibited viscoelastic behavior, with pressure increasing viscosity—up to 4.5 in agar and twice as much in agar-collagen fluid gels—and samples transitioned from Level 2 to Level 3, according to the International Dysphagia Diet Standardization Initiative (IDDSI) testing. Furthermore, pressure-induced structural changes enhanced fluid gel stability under dynamic conditions, increasing it from 74.11% to 84.98% in agar and from 48.85% to 68.08% in agar-collagen fluid gels. These findings offer valuable insights into how post-processing high-pressure homogenization can reduce droplet size, enhance palatability, and preserve swallowing safety, influencing the properties of formulated fluid gels without requiring additional thickeners.