Effect of addition of human saliva on steady and viscoelastic rheological properties of some commercial dysphagia-oriented products

Abstract

Three commercial thickened fluids were rheologically characterized before and after addition of unstimulated human saliva to improve the further development of better products in dysphagia management by taking into account the dynamic process of bolus flow and the effect of saliva. Instant purées (vegetables and beef (VB), vegetables and codfish (VC) and chicken with rice and carrots (CR)) were prepared and mixed with water or unstimulated saliva from five healthy individuals. Steady and dynamic rheological properties were evaluated, and composition of saliva from five donors was determined. Control purées had shear-thinning behaviour and showed a liquid-structured character with different viscoelastic parameters. All the water samples showed significant differences in the steady and viscoelastic parameters although not so notable as those produced by saliva addition. Thereby, addition of saliva produced a remarkable change in: viscosity (at 0.1, 1, 10 and 50 s−1), consistency index (K) and flow behaviour (n), and, in the conformational structure (decrease of maximum stress amplitude (σmax) and maximum complex modulus (G*) and increase in loss factor (tan δ) of all the three purées, especially in CR. VC and CR purées showed an increase in degree of structural deformability (higher γmax). High variability was found in the saliva composition, specifically in α-amylase activity, which might affect the rheological behaviour of these commercial products. Therefore, structural changes produced by saliva addition should take into account to design safer dysphagia products although this inter-individual effect should be studied with a larger number of individuals to obtain more relevant conclusions.