Insights into the Dynamics of Oral Lubrication and Mouthfeel using Soft Tribology: Differentiating Semi-fluid Foods with Similar Rheology

In-mouth lubrication or ‘oral tribology’ is believed to be a major contributor to the perception of surface-related mouthfeel attributes such as roughness and astringency. In this work, commercial soft-food systems – custards, yogurts and thickened creams, each formulated at varying fat levels with the aim of maintaining consumer acceptability – are characterized using rheology and soft tribology to gain insight into the physical origins of mouthfeel and the dynamics of oral lubrication, including the role of saliva. It is shown that, despite generating similar bulk rheological profiles (oscillatory and steady shear flow properties), foods within each product series exhibit unique tribological properties, attributed to the preferential entrainment of different phases and components at narrowgap. Food-saliva interactions are also shown to play a crucial role in determining transient lubrication properties, which may reflect dynamic oral processes. We explore the use of tribology to differentiate rheologically similar products as a starting point to develop improved approaches for investigating tribological processes occurring in the mouth during food consumption. Challenges associated with the application of tribology in this context are also discussed.