Hydrocolloid Effects on Shear and Extensional Rheology

Thickened beverages are a key element of dysphagia management, and their rheological properties determine how successfully they are swallowed. This study investigated the shear and extensional rheological behaviors of thickened beverages prepared with a broad range of hydrocolloids—modified starch (STA), xanthan gum (XAN), konjac gum (KJC), tara gum (TG), sodium alginate (SA), iota carrageenan (IC), sodium caseinate (SC), high methoxyl pectin (HMP), carboxymethylcellulose (CMC), hydroxypropyl methylcellulose (HPMC), and methylcellulose (MC). Each fluid was prepared to a consistent apparent shear viscosity at a shear rate of 30 s⁻¹. Shear thinning behavior varied across hydrocolloids, with XAN, TG, and KJC displaying pronounced shear thinning compared with SC and HMP. In extensional rheology measurements, capillary breakup times of HPMC, CMC, and MC were much higher than other tested hydrocolloids, with STA displaying the lowest breakup time. Extensional viscosity extracted between Hencky strains of 5.0–7.5 confirmed this trend as HMPC, CMC, and MC again possessed the highest extensional viscosity, while STA possessed the lowest. Comparison of shear thinning index with extensional viscosity revealed no relationship between the two across the hydrocolloids compared. These results suggest that shear and extensional rheology measure distinct properties of thickened fluids and suggest that optimization of these properties can improve the performance of thickened fluids for individuals with dysphagia.