[in Japanese]

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In 9 healthy dentate, the hardness of 31 foods before and after chewing until swallowing threshold was measured by the creepmeter, and the number of chewing stroke until swallowing threshold was counted in order to investigate the change in rheological properties by mastication. Masticatory performance in each subject was measured by the sieving method suggested by Kapur et al.
The results obtained are as follows.
1. The hardness of each food before chewing corresponded with the grades of masticatory difficulty of the food intake questionnaire.
2. The number of chewing strokes until swallowing threshold varied depending on the hardness of each food before chewing.
3. The hardness of 31 food bolus in swallowing threshold after chewing was less than 30kPa, independently of the degree of food intake difficulties of the questionnaire on masticatory function.
4. In peanut mastication, there was statistically significant correlation between the number of chewing strokes until swallowing threshold and masticatory performance (r=-0.87, p<0.01).
In the study, the result showed that the decision indicator in swallowing threshold was the hardness of bolus. Moreover, it was suggested that the hardness of bolus in swallowing threshold and the number of chewing strokes until swallowing threshold are useful for evaluation of the function.

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Rheological properties of several food products for people with mastication and swallowing difficulties were studied using compression test and dynamic viscoelasticity measurement. We tested various Kissei's products including fish surimi gels, pastes of fish or meat dishes, dessert jelly, mousse, and pudding. For all the products, the breaking stress was below 5×104N/m² indicated as the guideline for the elderly with mastication difficulty which is determined by the Ministry of Health and Welfare. Most gel type products exhibited lower firmness value than 1×104N/m2, that is the line for mastication and swallowing difficulties. Less frequency dependence of storage modulus, which is a typical gel characteristic, was commonly observed for paste-type and dessert products. However, the absolute value of storage modulus varied by hundreds. Low frequency region (-0.01 rad/s) corresponded with leaving condition of food before consumption, middle frequency around 1 rad/s relate to chewing, and higher frequency likely corresponded to swallowing condition. The stable storage modulus for wide range of time scale may be required for foods easily consumed by people with mastication difficulty.

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