Institutionalized Elderly are able to Detect Small Viscosity Variations in Thickened Water with Gum-based Thickeners. Should Texture Classifications be Reviewed?

Background: The prevalence of dysphagia is very high in institutionalized elderly. Knowledge of the rheological and sensory characteristics of the various thickeners is limited, although it has been seen that there are differences between the rheological behaviors of different gum-based thickeners with different composition. We have not found sensory studies of viscosity in institutionalized elderly. Our hypothesis was that viscosity ranges established by the scientific societies seem to be very wide and individuals might be able to detect small differences within the same texture range. The objectives of our study were comparing the rheological characteristics of two commercial gum-based thickeners with different composition, dissolved in water under standard conditions, and checking whether it could be possible to detect different viscosities within the same texture (nectar and honey) with the use of sensory analysis (both with adults and elderly). Methods: Two commercial thickeners based on gums (NC and RC) were studied analyzing their viscosity in water with different concentrations (shear rate: 50 s-1; temperature: 22-25°C). A sensory analysis involving 26 elderly and 29 adult controls was carried out to evaluate whether differences within nectar and honey textures among gum-based thickeners could be distinguished. Results: As the shear rate increases, viscosity decreases (non-Newtonian and pseudoplastic behavior). At the same concentration, each thickener produces a different viscosity (p<0.05). Institutionalized elderly detected viscosity differences in nectar range of 49.9 (2.5) mPa·s (p<0.05) y 102.2 (4.7) mPa·s (p<0.0001). They also detected viscosity differences in honey texture range of 134.6 (9.7) mPa·s (p<0.05) y 199,3 (9,2) mPa·s (p<0.0001). Their caregivers also detected viscosity differences in both viscosity ranges (p<0.0001). Conclusions: Our results suggest that the accepted viscosity ranges for the different textures might be too wide because institutionalized elderly and their caregivers are able to discern small differences in viscosity in nectar and honey textures. Gum-based thickeners with different composition showed differences in viscosity capacity, so they are not interchangeable.