Physicochemical and rheological interactions between chia seed mucilage and whole human saliva

Chia (Salvia hispanica) produces highly nutritious seeds which, upon dissolution in water, form characteristic hydrocolloidal mucilages. Understanding the behavior of these systems during oral processing could lead to solutions regarding salivary substitutes for dysphagia-management formulations. This is a study of the physicochemical and rheological properties of chia seed mucilages (CSM), and of their mixtures with unstimulated whole human saliva (UWHS), as to gain insights into their behavior during oral processing, and their potential of the latter's modulation. CSM dispersions (0.01–2% w/v) demonstrated mild acidic buffering, with pH values decreasing from 7.07 to 6.33, and a significantly negative zeta potential (−45 to −22 mV), thereby confirming the anionic polyelectrolyte characteristics of the system. Diffraction studies show the formation of extended polymeric clusters in the range of 100 μm. The low intrinsic viscosity of its purified polysaccharide at 0.83 dL g−1 suggests an open structure. It forms shear-thinning dispersions, whose low-strain rate viscosity lies between 10 and 1 Pa s−1 at 1- 2% chia concentration. Mixing with saliva results in a reduction in viscosity, attributable to the dilution of the highly extended polysaccharide. The filaments formed by chia mucilage show concentration-dependent relaxation times, ranging from 2 to 15 miliseconds. Mixing with saliva increases the filament break-up time and relaxation time to the order of seconds, highlighting the differences between shear and extensional rheology regarding chia mucilage mixing with saliva.