In-vivo visualisation of mouth–material interactions by video rate endoscopy

Results are reported for the first time on the use of an in-vivo fluorescence imaging technique to visualise residue in the oral cavity after oral processing of model fluid foods. A rigid rod endoscope is mounted such that all major axes of motion (pitch, yaw, roll, forward/reverse) can be exploited allowing comfortable viewing conditions for the subject during extended viewing periods. The technique has been applied to investigate the in-mouth behaviour, the distribution and clearance, of a range of homogeneous fluid foods in a subject. The results indicate that, for a range of different CMC solutions of varying citric acid content, viscosity is a key indicator for initial residue amount whereas salivary flow rate was shown to have little or no effect on initial deposited amount. However, salivary flow rate was found to have a strong influence on how quickly material was cleared from the oral cavity, with higher rates leading to faster clearance. The technique was also used to follow the in-mouth behaviour of bulk samples of corn and castor oil. Rapid emulsification on oral processing was observed, with smaller average droplet size observed for the lower viscosity oil. This work demonstrates the potential of this technique for investigating the range of processes that occur in the mouth during food processing and opens up new possibilities to increase our understanding of food material behaviour and its potential impact on the sensory perception of foods.