Masticatory movement rhythm before and after perception of bitterness

Abstract

This study aimed to clarify the masticatory movement rhythm before and after the perception of bitterness in food. Twenty-two healthy adults were asked to chew bitter and non-bitter gummy jellies, and the movement of the incisal point was recorded. Recordings were first performed during mastication of non-bitter gummy jelly （mastication A） followed by mastication of bitter gummy jelly （mastication B）, with a 5-minute interval between recordings. Subjects were asked to press a switch when they perceived bitterness, and 10 cycles starting from the 11th cycle before pressing the switch were defined as pre-bitterness, and 10 cycles starting from the 2nd cycle after pressing the switch were defined as post-bitterness. Next, for these ten cycles, the opening, closing, occluding, and cycle times were calculated. Further, the coefficient of variation （CV） was obtained from the mean time of the ten cycles and its standard deviation. The mean value was considered a parameter of movement rhythm and the CV as a parameter of stability of the movement rhythm. The values of parameters representing movement rhythm and its stability were compared between mastication A and B. The movement rhythm and its stability in mastication A and B were similar before bitterness recognition, with no significant differences. After bitterness recognition, the values of both parameters representing movement rhythm and its stability were larger in mastication B than in mastication A, with significant differences for all parameters, except the CV of the closing time. These findings suggested that food taste, especially bitterness, affects the movement rhythm during chewing.