Relationship between Physical Properties of a Food Bolus and Initiation of Swallowing

Abstract

To clarify the relationship between the physical properties of a food bolus and the initiation of swallowing, we measured the texture of food boluses collected from the oral cavity at three different stages of mastication: M stage, the halfway stage of mastication; L stage, immediately prior to swallowing; and +20% stage, the number of chewing strokes 20% beyond a point at which swallowing would usually occur. Eleven healthy adult participants masticated highly adhesive rice cakes (RC) , hard and brittle peanuts (P) and hard biscuits (HB). The texture of the bolus was measured by texture profile analysis. Hardness of the bolus decreased significantly from the M to L stage during mastication of all three types of food . This finding suggests that the decrease in hardness of a bolus may be a necessary factor for the initiation of swallowing, although it is not a sufficient factor by itself for the initiation of swallowing. For both the P and HB boluses, adhesiveness had a maximum value at the L stage immediately prior to swallowing, and cohesiveness increased significantly from the M to L stage. In contrast, adhesiveness of the RC bolus decreased significantly (p<0.001) from the M to L stage, with cohesiveness remaining unchanged. These findings suggest that the initiation of swallowing during mastication of hard and brittle food commences once a clump bolus formed, while swallowing of highly adhesive food is triggered when adhesiveness of the bolus is sufficiently reduced to meet the swallowing threshold.