SWALLOW THRESHOLDS IN HUMAN MASTICATION

Brazil-nut particles were broken down and classified by sieves into fo ur classes of particle size. Samples of these classes were suspended i n plain yoghurt in varying concentrations and presented to nine humans for chewing. Both the number of chews made before swallowing and the time needed to swallow increased significantly with particle size and concentration but the chewing frequency (number of chews/time) decreas ed. The rate of change of the chewing frequency, averaged over the che wing sequence (chewing frequency/time), was calculated for each food i nput and termed the swallowing index. This index did not differ signif icantly for concentrations above 20%, but increased sharply at lower c oncentrations. These results were interpreted in terms of a model in w hich food is swallowed only when particles are both small enough and s ufficiently lubricated. For our food mixture, the lubrication threshol d was satisfied by a 20% concentration and the particle-size threshold was 1.4 mm. Chews made with concentrations lower than this and contai ning smaller particle sizes were few in number and slow, reflecting th e need to detect particle size with the oral mucosa.