Keiji Yanagisawa

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.

To investigate the effect of ingested food texture on tongue activity during mastication in humans, the electromyographic (EMG) activity was recorded by surface electrodes from the skin over the mylohyoid muscle (MH), masseter muscle (M) and anterior digastric muscle (Da) during mastication ofthree kinds of food (gumi candy: G, peanuts: P, rice cake: RC) in eleven adult subjects. The texture ofthese foods was measured according to the texture profile analysis. P was the hardest food, while RC was the most adhesive of the three. The amplitude of M-EMG decreased significantly during P mastication, while the amplitude of Da-EMG decreased significantly according to the progress of mastication of G, P and RC. The amplitude of MH-EMG decreased significantly during mastication of G. In contrast, the amplitude of MH-EMG increased significantly during mastication of P and RC, with an especially marked increase in amplitude observed in the late stage of chewing during mastication of RC. These results suggest that tongue activity in the late stage of chewing just before swallowing may be affected by the texture of the triturated food in the oral cavity.