Implementation of an ultrasound method on a custom-built tribometer to investigate tongue-palate friction during food oral processing.

The sensitivity of tongue mechanoreceptors to the amplitude and frequency of mechanical stimuli strongly impacts food texture perceptions. In this work, a custom manufactured tribometer was used to explore the potential of an ultrasound (US) method for monitoring friction phenomena between an artificial tongue and palate. Polyvinyl alcohol cryogels were used as artificial tongues, with roughness varied in agreement with human tongue papillae height (20-140 μm). The lubricating role of liquid foods was investigated with Newtonian solutions of glycerol (1-1400 mPa.s). Under the artificial tongue, a single-element US transducer was used as both transmitter and receiver to monitor the variations of the time-of-flight (ΔToF) of the reflection of compressional waves (central frequency 5 MHz) against the artificial palate. ΔToF was compared to force and acceleration measurements recorded all along the experiments. Both the roughness of artificial tongues and the composition and thickness of the lubricating film drastically influenced the reciprocal forces and vibrations at tongue-palate interface. Concomitant variations of ΔToF were observed, induced by displacements of the artificial palate, with peak values ranging from 4.5 to 50.1 ns throughout the different experimental conditions. A 40-120 Hz bandpass filter on ΔToF made it possible to isolate fluctuations ranging from 0.7 to 10.4 ns, induced by vibration events due to stick-slip during dynamic friction. This study demonstrated the potential of the US method for exploring the respective contributions of the characteristics of foods and of the tongue on biomechanical and frictional phenomena involved in texture perceptions.