Study on rheological behavior of stirred yoghurt for dysphagia patients.

For dysphagia patients, diet management is a highly effective and well-accepted therapeutic method. Stirred yoghurt is particularly suitable due to its mouthfeel, flavor, and nutritional benefits, especially its increased viscosity compared to milk. However, despite extensive research on yoghurt rheology, a comprehensive understanding of its thixotropy and yield behaviors remains limited, hindering the rational design of texture-modified foods for dysphagia management. This study first investigated the viscosity and viscoelasticity of four yoghurts with different formulas (rich-textured "Indulgent" yoghurt, Y1; starch-containing yoghurt, Y2; light-texture fermented yoghurt, Y3; vitamin D-fortified yoghurt, Y4) through steady-state shear, frequency sweep and creep-recovery tests. Then, the hysteresis loop and thixotropic recovery tests were used to determine the thixotropy of yoghurts. Yield behavior was further evaluated and compared across six methods, involving creep, stress ramps, step shear rate, steady-state shear, amplitude sweep and stress bifurcation. According to the International Dysphagia Diet Standardisation Initiative framework, Y1, Y2 and Y4 were all classified as level 4. However, rheological analysis revealed that Y2 exhibited significantly higher thixotropy and yield stress, corresponding with its higher link density as determined by confocal laser scanning microscopy. And the yield of yoghurt was a process, with Y2 and Y4 exhibiting brittle yield, while Y1 and Y3 being ductile yield. This study provides novel insights into yoghurt microstructure-rheology relationships and offers scientifically robust guidance for tailoring diets to dysphagia patients with diverse conditions.