Effects of Filtered Air- and Bone-conduction Sounds’ Presentation in Mastication on Food Texture
Authors: Nakamoto Hiroyuki , Kawanishi Kento , Hirata Ichiro 
Published: October 2023

Food texture is an essential sensation for food palatability, as well as taste and aroma, and is particularly important for solid foods. Among food textures, crispness is one of the most popular food textures in various countries. There are many snack foods with crisp textures in the market. They contribute to the sales amount. Hence, food companies need to develop new snack foods with good crispness for consumers' palatability.For mechanical textures, humans generally perceive force, bone-conduction sound, and air-conduction sound through the senses of tactile and hearing. This indicates that food texture is a multisensory perception. There are some reports that a high-frequency sound changes food texture to make it crispier. These reports showed that the filtered sound parameters of one of the senses changed the texture of the food. It has the potential to add a crisp texture to the original texture. In comparison with other languages, the Japanese language has many food texture descriptors of 445. Crispness descriptors such as saku-saku and kari-kari have differences from each other. Native Japanese speakers use the texture terms properly. The influence of the filtered masticatory sound on the crispness descriptors in Japanese is unclear.This study investigates the influence of air- and bone-conduction sounds on crisp texture by sensory evaluation. Air-conduction sounds during mastication are converted into digital data by a microphone. The sound data are filtered by high-pass or low-pass filters and are presented to the participants of sensory evaluation by a headphone or a bone-conduction earphone. For comparison, the sound data were also presented without filtering. This process from the conversion to presentation is performed in real time. The sample of sensory evaluation used nine commercially available foods; potato chips, hardtacks, thin rice crackers, pretzel sticks, thin cookies, sablés, thick rice crackers, deep-fried cookies, and stick-shaped sweet potato chips. Participants were eight students aged 22.9 ± 0.83 (mean ± standard deviation). They bit each sample three times and recorded the degree of texture on the visual analog scale of three texture descriptors; saku-saku, kari-kari, pari-pari.In the results of the sensory evaluation, saku-saku had no significant influence by the low-pass or high-pass filter and the headphone or bone-conduction earphone. On the other hand, low-pass filtered sound decreased the evaluation values of kari-kari and pari-pari of most samples by the headphone. This suggests that saku-saku tends to be influenced by the perception of force than air- and bone-conduction sounds. Kari-kari and pari-pari were influenced by sound. Some samples such as thin cookies and sablés had a difference between the influence of low-pass and high-pass filters by the headphone. Kari-kari and pari-pari are sensitive to the frequency of the sound. Since there are different tendencies among the three crispness descriptors, the effective addition of crispness by sound requires a detailed design of the filter frequency for each object descriptor in Japanese.