Effects of Addition of Water on Masticatory Behavior and the Mechanical Properties of the Food Bolus

To elucidate the effects of water on the mechanical properties of the food bolus, the texture of the bolus was assessed. Thirteen adult subjects were instructed to chew 6 g of two test foods, a biscuit and rice cake, with and without water (2 mL). In the early, middle and late stages of mastication, subjects were instructed to spit the food bolus into a cup. Texture parameters (hardness, adhesiveness and cohesiveness) of the bolus were identified by texture profile analysis. Addition of water significantly ( p >0.001) decreased the number of chewing strokes (NCS) until swallowing for both test foods. Hardness of each of the two test food boluses decreased during mastication regardless of the presence or absence of water. Adhesiveness and cohesiveness of the biscuit bolus increased, whereas those of the rice cake bolus decreased regardless of the presence or absence of water. There were no significant differences in the three texture parameters immediately before swallowing for both food boluses with and without water, although the NCS until swallowing decreased during mastication with water. These results suggest that the presence of water and saliva accelerates bolus formation for swallowing the biscuits and rice cakes studied.