A Novel Experimental Set Up for In Situ Oral Lubrication Measurements

Oral lubrication has attracted a growing research interest in recent years because of its importance in influencing food texture and mouth-feel sensation. A number of tribometers have been developed for oral tribology studies, but all are designed for in vitro applications only. In this work, a new experimental set up has been established for in situ oral lubrication measurements; and further to determine oral lubrication as influenced by food consumption in relation to texture and mouth-feel. The design was based on a mechanical coupling between a texture analyzer and an intra-oral pressure sensor, and on a simultaneous digitizing of signals from both devices. Feasibility and reliability of the set up was firstly tested using hard–hard frosted glass surfaces with varying sliding speeds and two different normal forces; then using pig’s tongue – polydimethylsiloxane soft surfaces with artificial saliva and food samples varying fat content at different sliding speeds. Consistent friction coefficients were observed in hard-hard surface lubrication tests and fat content-dependent friction coefficients were seen in soft surface lubrication tests. After these, in situ friction coefficients were measured in 10 healthy subjects, both under unstimulated oral conditions and after consumption of fluid foods. It was found that friction coefficient measured with no food consumption (unstimulated) was correlated to the salivary viscosity as well as salivary flow rate. The oral friction coefficient showed a strong correlation with the sensory intensity perception of astringency and slipperiness. Results from this work demonstrate that this simple experimental set up is feasible and reliable. Our work provides a new experimental technique for oral lubrication studies in relation to the controlling mechanisms of oral sensation of food texture and mouth-feel.