Abstract
The objective of this study was to clarify the influence of food firmness in cooked rice on mastication. We prepared four rice samples by cooking with different water contents (1 .2, 1.5, 3.0 and 10.0-times water to rice weight). The firmness of cooked rice samples were evaluated using a rheometer. We used electromyography (EMG) to record both sides of the masseter and temporal muscle activities while young female subjects masticated 5 g of each sample and 10 g of the softest rice gruel. Firmer rice samples required more chews, longer mastication time, and greater EMG amplitude. Consequently, the firmer samples exhibited more muscle activity and longer total EMG-burst duration until swallowing. Mastication of 10 g gruel (× 10.0 water) resulted in 1.4-fold values in the number of chews, mastication time, and total muscle activity compared to 5 g gruel. These findings suggest that rice firmness affects mastication more than the bolus amount of cooked rice. Our results suggest that ingesting small amount of gruel more frequently requires more mastication than taking large bolus to reduce the number of boli.
