Agar-collagen fluid gels as a dysphagia food: Rheological characterization vs fiberoptic endoscopic evaluation of swallowing

The completely different structuring approach of the fluid gels makes them rheologically-tunable systems with a high underexplored potential for application in dysphagia diets. The aim of this study was to characterize the swallowing behavior of high-protein collagen (20 %w/w) fluid gels structured with various agar concentrations (0.5 to 2.5 %w/w) using different analytical methods. The oral performance during different phases of dynamic swallowing processes was characterized by rheological methods (shear yield stress, shear-dependent viscosity, strain and frequency-dependent viscoelasticity, shear recovery behavior), International Dysphagia Diet Standardization Initiative tests (IDDSI) and fiberoptic endoscopic evaluation of swallowing. In addition, the stability and particle size of the systems were characterized. All samples were stable and the polydispersity increased (span from 1.7 to 3.2) with increasing agar concentration. Fluid gels displayed low yield stress values (<2.0 Pa), good shear flowability and high shear recovery behavior which is well-matched with the facilitated swallowing process. The IDDSI tests showed that varying the agar concentration yields fluid gels with different thickness levels, suitable for mild and moderate dysphagia. The results of the endoscopic swallowing assessment test correlated with the results of the rheological analysis and confirmed the suitability of these systems for safe swallowing.