The cervical auscultation method was applied to investigate sounds generated while swallowing various foods with different consistencies, including water, yogurt, and konjac jelly. Dynamic viscoelasticity, viscosity, and compression or penetration force of yogurt and konjac jelly were measured. The yogurt was fractured by the tongue while swallowing, whereas konjac jelly was not. Significant differences were detected in the durations of the swallowing sound component, generated by food bolus flow through the pharynx. The root mean square amplitude of the component that was attributed to the water flow was significantly higher than that for the flow of other food samples. No significant differences were detected in the duration of sound components appearing before and after the bolus flow or in the total duration among the food samples. Scattered or heterogeneous food bolus flow appeared to significantly reflect the duration of swallowing sounds, generated by the food flow.
Nursing-care foods are in much demand in the expanding elderly society. Ease in swallowing is an important factor for such foods and it is strongly correlated to food texture. Our results indicated significant differences in the duration and amplitude of swallowing sounds, generated by food bolus flow through the pharynx. Because the swallowing sounds depend on the food texture, monitoring such sounds can aid in designing and evaluating the foods to ease swallowing. The method used in this study is noninvasive and cost effective and is therefore practical for use in the food industry. The dependence of the swallowing sounds on human subjects can be analyzed if the data from a greater number of subjects are gathered.