Rheology for Safe Swallowing 1

In aged society, the number of persons with difficulty in mastication and swallowing is increasing, and the aspiration-induced pneumonia is one of the top causes of death in the elderly. Although the detailed mechanism of aspiration is still not well understood, great efforts have been done to prevent the aspiration, and thickening of bolus has been found effective to reduce the risk of aspiration. It was pointed out earlier that excessive thickening reduces the palatability and the intake of fluids leading to dehydration and malnutrition and to formation of the residue as a risk of aspiration. In the present review, the physiological aspects of food oral processing conducted in the mouth by teeth, tongue, saliva have been introduced, and practical evaluation methods of rheological properties used in hospitals and nursing care facilities are described. Viscosity of commonly used polysaccharide-based thickening agents is described in relation with yield stress, thixotropy together with tribological aspects which play important roles in swallowing. To improve the control of texture, new thickening agents and modifying methods of rheological properties are described. Emerging methods to study the swallowing process have been also discussed. Finally, the importance of integration and collaboration of different disciplines is emphasized.