It is necessary to control the rheological properties of bolus to prevent aspiration. To know the risk of aspiration for each person with difficulty in mastication and swallowing, it will be effective to use a test fluid which enables doctors to judge the safe range of the viscosity based on videofluorography. Since the knowledge of dominant factors which govern rheology is required, effects of shear rate, cooling rate, concentration of polysaccharides, coexisting seasonings on viscosity and viscoelasticity are overviewed. Since chemical senses are also known to affect the swallowing behavior, the relation between texture and flavor release is described briefly. Mixture of polysaccharides, proteins and fluid gels are overviewed as texture modifiers. Acoustic analysis of swallowing, extrusion method, a falling needle viscometer, tribological study on frictional coefficient of bolus are also described as each method is expected to be a useful tool to understand the complicated aspect of the disorder in mastication and deglutition. Mastication and swallowing of minced foods and model food gels are also described. Finally, the importance of the communication and collaboration between different disciplines is emphasized. Practical Applications Polysaccharides have been used to modify the texture of foods. It is necessary to know how these polysaccharides influence the swallowing behavior to design foods for elderly. Since the texture of foods is influenced by taste, aroma and conversely these are influenced by texture, the knowledge on the relation between texture and flavor release is crucial to manipulate the foods to reduce the risk of aspiration. Some examples which are expected to be helpful to design foods for elderly are shown.

No abstract

The temperature and frequency dependence of the dynamic shear modulus, strain-optical coefficient, and the optical transmission of κ-and ι-carrageenan aqueous solutions were measured in order to clarify the gelation mechanism. The growing of the gel network and the effect of cation species (K, Cs, and Ca) and the amount of added KCl are discussed on the basis of the correlation between the shear modulus and strain-optical coefficient. For all samples, these correlations can be described by a power function in the low-temperature region in the gel state. The exponent can be interpreted as a characteristic parameter reflecting the growing process of the gel network. We found two groups in terms of the value of the exponent. In the case of 2.0 wt % (high polymer concentration) K-form and Cs-form κ-carrageenan, the exponent is much higher than unity, but in the case of 1.0 wt % K-form (low polymer concentration) κ-carrageenan with added KCl and 2.0 wt % K-form ι-carrageenan, it is close to unity. For the former group, the stress required to induce the unit orientation increases, while for the latter group it does not increase much with decreasing temperature. In other words, the structure inside cross-link region changes markedly during the growing process of gel network only for the former group. We concluded that increasing schemes of the number of aggregated helical molecules during the gel growing process strongly depends on the cation species and carrageenan type.

No abstract

No abstract