Texture is important in terms of both food palatability and the safety of eating. Recently, the importance of texture has been emphasized for the development of nursing-care foods in this aged society, where the number of patients with mastication and swallowing difficulties is increasing. Texture design of these food products is now one of the most important tasks in the food industry in Japan. Texture of these food products should be modified by modulating viscoelasticity using hydrocolloids so that they can be easily transformed into ‘ready-to-swallow’ bolus during oral processing. This article reviews the importance of texture as an essential attribute of foods and also the usefulness of hydrocolloids as an ingredient to modify food texture. The article also covers recent trials by the author’s research team on bolus rheology and in vivo acoustic analysis during swallowing. The trials are to find some objective parameters describing the mastication and swallowing eases as an alternative to conventional bulk rheology and subjective sensory analysis.
The dielectric properties are related to other physical variables of a sample, such as its structure, composition, phase, and temperature. Therefore, an analytical method that uses these properties can be an effective means to determine the structure of a sample. In addition, nondestructive measurement is possible by this method. In this study, we attempted the nondestructive measurement of air bubbles in yogurt using dielectric properties, namely, complex electric capacitances. The samples were prepared by dispersing air bubbles in base yogurt. The effects of the air volume and the air bubble size in yogurts on dielectric properties were investigated. Consequently, the capacitance increased with an increase in air volume in yogurt. Moreover, the capacitance increased with decreasing diameter of air bubbles in yogurt. In this study, it was considered that the electrokinetic phenomenon generated at the interface of the gas and liquid phases contributed to the increase of the capacitance. The complex electric capacitances of the base yogurt and the air-mixed yogurt were measured in the range of 50 Hz–1 MHz. When a Cole-Cole plot was drawn from the measured data, a clear difference was seen in the sizes of the circular arcs of the two samples. In the frequency range of the circular arc locus of the Cole-Cole plot, the capacitance of air-mixed yogurt was always greater than that of the base yogurt. From the above-mentioned result, it was clarified that air bubbles in the yogurt could be quantified by measurement of the dielectric properties.